Impact of the clouds of volcanic aerosols in Italy

Natural Hazards 11: 135-161, 1995. Kluwer Academic Publishers. Printed in the Netherlands.

135

© 1995

Impact of the Clouds of Volcanic Aerosols in Italy During the Last 7 Centuries DARIO CAMUFFO and SIL VIA ENZI National Research Council, CNR-ICTlMA, C. so Stati Uniti 4, 1-35020 Padova, Italy (Received: 14 January 1994) Abstract. Intense natural pollution has occurred in the past in Italy corresponding to intense volcanic activity, which appears to have diminished somewhat in recent times. Between 1500 and 1900, Etna, Vesuvius, Vulcano and Stromboli, plus volcanoes outside Italy were very active and there are numerous, well documented episodes of atmospheric acidification which caused widespread damage, especially to the vegetation. Other than the acid rains, volcanic emissions also caused so called dry fogs which consist of a more or less dense mist composed of foul smelling gases and aerosols, characterized by a reddish color, that could appear and persist when the relative humidity was low as shown by measurements taken on such occasions. This phenomenon appeared most frequently at the beginning of the hot season. In fact, volcanic clouds of gases and aerosols formed especially when the Tyrrhenian sea water was relatively cold giving rise to very stable atmospheric conditions locally and the summer anticyclone meant that the winds were calm. Under such conditions the emissions of Stromboli and Vulcano, especially those emitted at low levels, remained entrapped in the stable layer, which were then transported towards the land reaching Northern Italy at a distance on the order of 103 km. The dry fogs could persist for days or weeks. Harvests were seriously damaged and frequently the crops were subsequently attacked by parasites. The leaves of the vegetation became discoloured with numerous punctiform lesions or gangrene at the edges of the leaves. The phenomenon was so frequent that, in texts on agricultural meteorology of the 1800s, a distinction was made between the caustic dry fogs which damaged the vegetation and damp fogs which instead were good for it. The most important episode occurred in 1783 due to the activity of Laki Grimsvotn (Iceland) with the contribution of Italian volcanoes. This dry fog lasted many months and affected the greater part of the northern hemisphere including Europe and Asia, harming people, animals and vegetation. Apart from paroxysmal cases, from the 1300s up to today, some tens of dry fogs have been noted, all of which have been sufficiently well documented. The frequency of these events culminated between the middle of the 1700s and the middle of the 1800s. There is reason to believe that this well documented phenomenon of the past, with sufficient volcanic activity, could recur on the meso and large scale; with present day activity the emissions continue to cause damage to vegetation, both in the Aspromonte mountains (Calabria, Southem Italy) as well as in other parts of Italy. Key words. Volcanic emissions, volcanic aerosols, dry fogs, volcanic hazards, volcanoes, Italy.

1. Introduction It is well known that the veil of dust emitted by explosive volcanic eruptions may

remain trapped for a long time in the stratosphere, affecting the earth's climate. This, and other similar effects related to climate changes were widely studied after Lamb (1970) pointed out the problem, joining the theory with the chronology of volcanic eruptions and dust veils in the atmosphere since A.D. 1500. In addition to affecting the climate, the volcanic eruptions are also responsible for emissions

136

DARIO CAMUFFO AND SILVIA ENZI

of gases and aerosols that may be trapped in the lower troposphere which, in the most severe cases kill people and animals, and cause severe damage to vegetation. The local or mesoscale effects in the troposphere are more often associated with continuous, non violent emissions and degassing of lava, than with the explosive eruptions which form dust veils in the stratosphere. The volcanic hazard from toxic clouds trapped in the lower troposphere has been less studied. Episodes of atmospheric acidification were recurrent not only in Southern Italy on the local scale near the volcanoes, but also in Northern Italy, where the clouds arrived after a transport on the order of 103 km. In the plain of Northern Italy these clouds can remain for a relatively long time, as the Alpine Chain forms a barrier against a further northward transport. This paper is focused on the documentation of the cases in which the acid clouds reached Northern Italy. In the past 5 centuries, activity of the Italian volcanoes (Fig. 1) has increased considerably compared to the last two millennia, although it has diminished in recent times. Etna was very active from 1500, Stromboli from 1580, Vesuvius from 1600 and Vulcano from 1700. This activity has been accurately reconstructed by various authors (Lamb, 1970; Simkin et al., 1981; Romano and Sturiale, 1982; Stothers and Rampino, 1983; Chester et al., 1985), some of whom were particularly aware of the problems related to the emission of aerosols into the atmosphere with the clouding over of the sky, the formation of extensive mists or the unusual reddening of the sky, especially at sunset. Numerous well documented episodes of acid rain occurred which caused damage to the vegetation and, to a lesser extent, to stone monuments (Camuffo, 1990, 1992). The first scientific description of acid rain can be found in the Treatise on Physics written by Fabri in 1670, as well as other detailed descriptions (e.g. Boerhaave, 1730; Crivelli, 1744). Pictorial reproduction is also interesting, and is particularly detailed and expressive in the painting by Gioacchino Toma (1880), 'Rain of Ashes from Vesuvius' which clearly shows an episode in the Naples area.

2. Examples of Dry Fogs Described from Northern Italian Sources Old descriptions of damage to the vegetation resulting from caustic winds are known in literature. Filiasi (1828) reported for example two events known from the literature, which occurred respectively in A.D. 936 and 968 (as a result of the eruption of Vesuvius) when a SW wind (called Garbino) destroyed the harvests. The author maintains that the same phenomenon occurred frequently during his time, in the Po Plain and in the countryside around Rome. Referring to the Garbino wind in the Po Plain, Filiasi (1828), said: "It would seem that it brings with itself a caustic element, which dries and burns all the grain". At the end of the 18th century, Toaldo (1789) called out numerous experiments, placing plants in various positions to determine the effect of the winds on vegetation. He obtained some positive results, but the method was not particularly convincing. There are further descriptions, mainly from sources in Northern Italy, where it

CLOUDS OF VOLCANIC AEROSOLS

137

tyrrhenian sea

Fig. 1. Map of Italy showing the volcanoes of Vesuvius (Ve), Vulcano (Vu), Stromboli (S), Etna (E), the Aspromonte mountains (A) and Padua (P). The majority of the cities cited in this paper are located in the Po Valley. Shading indicates the mountains of the Alps and Appenines.

is said that similar damage was due to the fogs. In 1689, at the beginning of June, the harvests were damaged, described by Fiandrini (18th century) and Toaldo (1797), both put the reasons down to the strange, unseasonal fogs. Ramazzini (1718), also wrote in the same year that a black rust ruined the entire wheat harvest leaving unusual signs on the plants. He suggested that this was due to a "corrosive, acid rust like the Stige waters and spirit of nitre and vitriol" and tried to reproduce the same effect in his laboratory, watering the plants with "vitriol spirit", obtaining similar effects. Valatelli (1803) wrote: "Some years, the fog ... in spring, and at the beginning of the summer at dawn, damages the crops while growing or at their maturation". Sometimes, there are specific references to the so called dry fogs. These reddish,

138


malodorous fogs which did not wet surfaces, persisting even into the middle of the day, and appearing even in the summer, were often accompanied by red dusks, a weak sun, solar and lunar halos, which caused damage to the vegetation and brought in their wake, epidemics. They were often being associated with storms. Scholars have known of the existence of dry fogs since the end of the 1700s, even though the causes were unknown then. For example, Orlandini (1853), gave the following description There are 'fogs which wet' bodies they touch and they are in the majority; but there are also dry fogs, whereby the hygrometer moves towards 'dry' ... How is it possible to explain, only in terms of the condensation of vapour and cooling, certain fogs which last a number of days under a temperature varying from + 1 to -6 [oq, for example, like the London fog of 1813? How is it possible to explain those which do not dissipate even with the great summer heat, like those that prevailed for some months in 1783? How can these effects be explained?

It is interesting to read some of the descriptions by direct witnesses, such as Gennari or Filiasi, for example. Gennari, a Padua chronicler, described the phenomenon in detail in his diary for the first time in 1783: Many days this month were also foggy at dawn and sunset, and the moon appeared ruddy and equally the sun that could be looked at without being blinded. The fog was high, dry and dense and this phenomenon was observed not only by us, but also everywhere in Italy, Germany and France, giving the opportunity for some astronomers and meteorologists, by their writings, to dissipate the fears conceived by the lower classes?

About thirty years later, the meteorologist Filiasi, seeing a similar phenomenon, wrote: "Among other things it began to get warm, and on the 10 and 11 [July 1814] the sky was obscured by a high, dry, reddish fog that made the sun murky, tinting it purple, bringing back to mind the celebrated one of 1783". The initial descriptions were only qualitative, while later it was verified in detail by instrumental measurements. The sources documenting the phenomenon are taken from accounts by authors who are essentially reliable in that they lived at the time of the event and so were eye witnesses. Furthermore, these witnesses can be considered 'competent' - at least with respect to the knowledge of the time - in that they were men of science and capable, as other parts of their descriptions demonstrate, of a critical and observational capability that could be defined as being 'modern'. The view of the most reliable meteorologists of the time is here reported from the writings of A. Secchi and F. Denza. Secchi (1866) specified that: "The above mentioned fog contains no vapour, because the psychrometer frequently indicates that it is dryer than usual". Denza wrote (1869): Whatever the origin or nature of the said dry fogs is, which up till now, we have not mentioned, they derive from a state of the atmosphere similar to that which has been observed many other times, and which a careful observer can witness more often than is ordinarily believed. It is, although less intense, of the same nature as the one of 1783, that persisted over the whole of Europe and in north America from the 24th May to the 8th October, and De Saussure suggested that it is caused from a dry vapour, called smoke by the mountain dwellers of Bern who, according to the illustrious Geneva meteorologist, 'is commonly called brouillard'. Nor does it differ from the one, which happened not long ago, the 11th September 1812, about which Gasparin talks, that when he passed into Ventoux mountain, met


139

a cloud which did not, in point of fact, wet his clothes, and did not bring about any reaction on the part of the hygrometer, and many other similar events are quoted in the more accredited works of meteorology.

The dry fogs were accompanied by many side effects, such as damage to vegetation, sometimes herbivorous animals became ill and even people were harmed; the frequency of storms increased, as will be shown.

3. Temporal Distribution of Dry Fogs In Northern Italy, from 1500 up until today, some tens of fogs have occurred that appear anomalous either because of the season or the region in which they occurred, or the duration or their effects. The most representative and best documented are shown in Table I. Fogs or haze inserted in this table, can be classified in different ways: - dry fogs correctly said to be of volcanic origin: caustic, reddish, with a low relative humidity; - haze due to which the visibility was reduced and when clearing could persist even under conditions of low relative humidity; - anomalous fogs for the season and area in which they occurred, or their frequency, but of climatic origin; - layers of volcanic aerosols, but in the upper troposphere or in the stratosphere, such to hide the sun or generate crowns and halos, but not giving rise to fogs at ground level.

Atmospheric optical phenomena associated with volcanic eruptions, such as solar halos, a dark red obscured sun, and purple sunsets, could be due either to the same reasons as those causing the anomalous fogs (and therefore confirming their volcanic origin), or to dusts and aerosols in the stratosphere generated by the eruption of distant volcanoes, and therefore completely foreign to the cause of the local fog or haze in question. To distinguish the dry fogs from others, above all in the period preceding the famous one of 1783, the criterion used was that the fog had to occur in an unusual period of the year and that specific mention had to be made of damage to crops, even though this selective criterion drastically reduced the number of acceptable events, in that it could only be applied to the summer period. Using such criteria, the fogs of 1374, 1499, 1587, 1592, 1648, 1682, 1689, 1710, 1735, 1775, 1780, 1783, 1785, 1786, 1791, 1814, 1816 and 1819 are recognized. After 1783, the expression 'like that of 1783' was frequently found, which constitutes :m excellent reference and excludes any possible ambiguity, and also because at that time, news was no longer given by inexpert chroniclers but by meteorologists of considerable experience. Such then were the fogs of 1794, 1802, 1803, 1805, 1812, 1814, 1821 and 1869. After the first quarter of the 1800s hygrometric measurements became ever more widespread and reliable (the August psychrometer appeared in 1825),

140

DARIO CAMUFFO AND SILVIA ENZI Table la. Phenomenology of the anomalous fogs. On the ground of the archival sources quoted in the bibliography, the following cases can be classified: L for Local, i.e. localities near the volcanic region, N for National, i.e. national localities far from the emission zone, W for Widespread, i.e. mesoscale relevance 1374*

Grain ruined because of continuous fog and rain; followed by famine in Piacenza (Locati, 1564). N

1462

July: cold with a lot of fog in Bologna (Ghirardacci, 16th century). In Naples on 8 August, the moon became blood red and in the following days the air became misty everywhere, as if there were clouds; these disappeared after the rains which followed (Tummulillis, 15th century). N

1465

In Naples in the month of September all the air suddenly became cloudy and misty for many days and nights and the sun on rising looked like a weak, non-luminous moon and at mid-day appeared pale and formed opposite shadows and it disappeared completely towards dusk. The 14th morning the sun looked yellowish and from noon to the evening it seemed blue behind the clouds and mist, but it did not shine brightly, and this lasted for almost ten days, with the air being still and absolutely no wind, and there were no other clouds, neither over the plain nor over the mountains, other than the haze (Tummulillis, 15th century). In Rome, the 14th September the sun during the day varied in colour from yellow-green to blue (Infessura, 16th century). Also in Bologna, for the whole of September, the sun was dark or blue and without heat, as if it were January (Nadi, 16th century). Still talking about Bologna sources, Ghirardacci (16th century) reports a wheat famine, without however linking this directly to the phenomenon, so that it can be said with certainty that the famine was caused by the fog. N-W The phenomenon was probably due to volcanic particles which had been trapped in the stratosphere.

1499*

June: wind from the NW, fog, drizzle in Forli; spring/summer: famine; August: plague in the Piedmont (Alessandrini, 17th century). May/June: fog in Orvieto 'burned' the grain; the grape harvest in Orvieto was also reduced (Ser Tommaso, 16th century). N

1511

Summer: continuous fog, rain, cold and late harvest; solar halo in May in Udine (Battistella, 1930). N

1587*

June 24: fog, extensive damage to the harvests throughout Italy (Bonoli, 1661). N

1592*

A summer fog dried the wheat in the Ravenna area (Fiandrini, 18th century). N

1620

From August 11 to 9 September, there was an 'unseasonal' fog in Modena; the 13 August fog, wind and hailstones near Modena, with cold mornings but becoming warmer in the aftenoons; up to the 16 August cold too, then the fog continued but the hot weather began; the 9 September the air cooled, but there was still fog (Spaccini, 17th century). N

1648*

June 23: in the night, fog 'fetid and rank' ruined the harvests causing famine in Romagna (Bonoli, 1661). N

1682*

Summer: fog 'dries' the mature grain in all Romagna ruining the harvest (Pasolini, 1701); Fiandrini (18th century) who, drawing on Pasolini, reports the same dating it 1683). N

1689*

June 24/25: fog damaged the harvest in Romagna (Fiandrini, 18th century). The dew caused black rust in the wheat (Ramazzini, 1718). A summer fog ruined the harvests and the fruit (Toaldo, 1797). N


141

Table la.

Continued

1690

At Modena, the dew caused black rust in the wheat as it did in the previous year (Ramazzini 1718). The author makes no mention of the dry fog phenomenon and no other confirmation has been found. N

1710*

Summer: Fog damaged the harvest in Lombardy and the Piedmont: various sources from northern Italy (all in Salmelli, 1986), carry news of ruined crops 'it is not known whether this is due to winds, fogs, or other black rusts which rained down' (Vercellone, 1721); from a hailstorm, from fogs and acid (De Conti, 1841), from fogs or 'acid' that damages the grains in the ears (Varese Chronicle). N

1734

August: continuous fog for three weeks in the Ravenna area (Fiandrini, 18th century). N-W? Note: 1733, dry fog in Europe? (Lamb, 1970); 1730-36, acid fallout in Greenland (Halmner et al., 1980)

1735*

In May, a SW wind blew for three days 'which seems that a caustic element brings dryness' and 'dries' the wheat (Muratori in Filiasi, 1828). This description however does not speak of fog, which Filiasi mentions, instead for the previous year. The same theory is mentioned by yet another anonymous author (1781) - probably Filias - in which it is said, taking for example the year 1735, that "such westerly winds a greatly feared which at times fall over [Lombardy and Emilia] blowing at the time of maturation of the ears, because they are dry and bring with them a certain caustic that damage the wheat ... ". Fog damaged the grain (Toaldo, 1784). N

1740

June: eight days of fog in Padua (Morgagni, 1740-1768). N

1748

Summer: fog in Padua (Toaldo, 1784; Morgagni, 1740-1768). N

1763

August: fog in Padua (Morgagni, 1740-1768). N

1765

August: fog in Padua (Morgagni, 1740-1768); 'universal' famine in Italy (Toaldo, 1784). N

1767

June: fog in Padua (Morgagni, 1740-1768; Toaldo, 1785)); August: catarrhal infections at Venice and Padua in September (Gennari, 1739-1800). N

1768

July and August: fog in Padua (Morgagni, 1740-1768). N

1774

A 'smelly fog' damaged the grain in mid-May. This was due however to the stagnation of rain water in the fields, followed by a 'blazing sun' (Toaldo, 1775). N

1775*

Summer: fog in Padua; June: a 'corrosive' fog damaged the wheat; August: fog damaged the maize in the Veneto (Toaldo, 1776). N

1780*

Summer: fog ruined the harvests in the Veneto (Toaldo, 1781). N-W? Note: Memorable day in New England (USA) without light (Corliss, 1983a); however, the two events are not necessarily linked.

1783*

Dry fog, persistent, reddish for the whole of the summer caused damage to the harvests, animals, people (Mantovani, 1886; Gennari, 1739-1800; Toaldo, 1784 and 1795; Orlandini, 1853; Lamb, 1970; Thordarson and Self, 1993). A 'dense and smelly' fog lasted for months in Sicily, Italy, France and Germany (Botta, 1834). Acid fallout in Greenland (Hammer et al., 1980). W

1785*

Summer: fog; August: "a burning haze produced a type of 'black rust' in many places, especially in the Polesine and damaged the maize and fruit" (Toaldo, 17661804; 1787). N-W? Note: In Canada some darkened days, yellow clouds (Corliss, 1983a); however, the two events are not necessarily linked.

142

DARIO CAMUFFO AND SILVIA ENZI Table la.

Continued

1786*

The wheat was scarce and infected by smut or blight; the maize yield was halved. The reason was due to damp, cool season, given that the summer was almost missing; the second harvests were also unsatisfactory (Toaldo, 1766-1804). N

1791 *

The source (Filiasi, 1828) makes reference to the news of 1735 and wrote that the maize had been ruined in Lombardy, in July 1791, 'for the same reason'. He does not mention any fog either, for that year. Toaldo (1793) also wrote that the wheat harvest was very scarce because the spring and the first part of the summer had been cold and damp. In his daily observations (Toaldo, 1766-1804) wrote: "from the 19 to the end of May there was a fog like the dry fog of 1783" and the mist was frequent throughout the summer. N

1794*

"Dry fog like that of 1783" associated to a "prodigious eruption of Vesuvius" (Toaldo, 1766-1804; 1795). N

1802*

August: fog similar to that of 1783 (Chiminello, 1804). N

1803*

April: reddish fog similar to that of 1783 (Chiminello, 1805). N

1805*

July: "reddish dry fog similar to that of 1783" (Chiminello, 1806). N

1807

June and July: some foggy days (4 and 5), (Bertirossi Busatta, 1807). N-W? Note: In Lisbon, the 6th June, a thick fog preceded an earthquake (Corliss, 1983b); however, the two events are no necessarily linked.

1810

During the winter, the spring and the entire summer: a hidden and hazy 'weak sun', fog and frequent rains (Bertirossi Busatta, 1812). N Note: 1811, red sunsets (Lamb, 1970). Volcanic emissions in the atmosphere probably andlor also in the troposphere, being responsible for the fogs.

1812*

"The haze of 1869 is of the same nature as that of 1783 and does not differ from that of September 1812 on Ventoso Mountain" (Denza, 1860). Dry fogs in July, and the maximum was on July 8th, at Modena (Northern Italy). Yellow weak sun in Italy and yellow fogs in Italy (Bonacini, 1939). N-W? Note: 1811 and 1813, red sunsets (Lamb, 1970).

1813

Summer: fog and haze, blood coloured moon, 'weak sun'. The wheat harvest was abundant, "but the grain was not very heavy, nor flourishing" (Penada, 1815). In Italy some darkened days (Stothers and Rampino, 1983); red sunsets (Lamb, 1970). N

1814*

July: weak or murky sun, dry reddish fog like that of 1783, damage to the harvests, cold and stormy, only 20 days of real summer (Penada, 1816; Filiasi, 1815). W Note 1: Red sunsets (Lamb, 1970). 3 July: New England and Canada sun obscured; the same thing in the same year in Borneo (Corliss, 1983a). Note 2: 1815, Acid rain defined as 'drying and caustic' and commonly called 'acid' (Filiasi, 1816). Effects on a global scale attributed to the eruption of Tambora (Lamb, 1970); acid fallout in Greenland (Hammer et al., 1980).

1816*

"The 9 and 10 July ruinous fogs that spoil every kind of fruit" (Penada, 1818). N

1817

January; fogs from Sicily as far and England (Filiasi, 1818). W

1819*

April: 'harmful fog' and 'damage' to vegetation (Penada,1821). N-W? Note: In November severe dark in northeast America (Corliss, 1983a); however, the two events are not necessarily linked.

1821 *

July: sun and moon surrounded by bloody halo August: a high fog similar to that of 1783 (Penada, 1822; Filiasi, 1821); one day of fog in July and one August in Udine (Venerio, 1851). Blue sun (Lamb, 1970). N-W? Note: 1822? sun obscured in northern Italy (Stothers and Rampino, 1983); bloody sun (Lamb, 1970).


143

Table la.

Continued

1822

In January, Vesuvius erupted lava and 'smoke', with a lot of dross and great sand turbines, that fell on Naples' (Bonucci, 1845). In May, four days with mist in the morning (Penada, 1823). The sun was obscured in northern Italy (Stothers and Rampino, 1983). L-N?

1824*

Spring: sun with white halos, one day of fog in June; July 'dry fog' in Tuscany (Filiasi, 1824); August: mist around the sun in central Italy (Lamb, 1970). N

1831 *

Extraordinary dry fog in Europe, North Africa, Siberia and America attributed to Vesuvius or to the underwater explosion of Sciacca (Lamb, 1970; Stothers and Rampino, 1983). In the Italian writings of the time however, no mention was found of dry fog. From 14 August to 27 of the following February, Vesuvius was active, emitting lava, smoke and ashes (Bonucci, 1845). In Modena, the year was characterized by fog and persistent haze; the sun was weak and bluish (Bonacini, 1939). In the summer, seven days of fog in Rome (Eredia, 1911), but only two days of fog in the morning in Padua (Conti, 1833) and two in Udine (Venerio, 1851). Red sunsets (Marangoni, 1884-85); in August intense light for a long time after the twilight and before down in Modena (Bonacini, 1939). W

1866*

February: "Red and hazy sun", "the fog is not affected by vapour because the psychrometer indicates that it is dryer than usual" (Secchi, 1866). In the months of January and February there were persistent and frequent fogs in Naples and Rome; often too in Palermo; solar halos (Zantedeschi, 1866). Fog or mist was frequent and persistent for almost the entire summer in Turin, with low relative humidity (Obs. BulL University of Turin, 1867). N

1869*

Dry fog, "The haze of 1869 is of the same nature as that of 1783" throughout the whole peninsula and in the greater part of central and western Europe; "the psychrometric observations presented the opposite trend to that it usually follows with the ordinary fogs?" (Denza, 1869); Dry fogs in July, with maximum intensity on 8 July; weak and yellow sun and widespread yellow fogs in Italy in July (Bonacini, 1939); red sun (Denza, 1869; Secchi, 1866); red sunsets (Lamb, 1970). W

1883/4*

Purple sunsets attributed to Krakatoa (Marangoni, 1884; Tacchini, 1884); persistent fog from November 1883 to January 1884, also with low relative humidity (Obs. Bull. University of Turin, 1883). Parhelium et halo in October 1883; frequent purple sunsets; frequent solar and lunar coronas in summer and autumn in Modena (Bonacini, 1939). Various effects on a global scale attributed to the explosion of Krakatoa (Lamb, 1970). In England dark, yellowish, dense clouds were seen, that gave a blackish rain (Corliss, 1983a); acid fallout in Greenland (Hammer et al., 1980). W

1886*

Fog in May, June and July in Turin (Obs. BulL University of Turin, 1887); a few days of fog in Venice in June (2) and July (4) (Zanon, 1927); no foggy days in Milan (Santomauro, 1957) and three during the whole of the summer in Rome (Eredia, 1911); fog from the 29/5 to 3/6 in Italy (Lamb, 1970). W Note: Diurnal darkening in Wisconsin (USA) the 19th March and in England in October (Corliss, 1983); however, the two events are not necessarily linked.

1890

Purple sunsets. In July, three days with thick fog at sunset and red sky at Modena (Bonacini, 1939). Frequent fogs in summer (11 days) in Rome (Eredia, 1911). N

1891

14 August, thick fog and purple sunset; several purple sunsets in Modena (Bonacini, 1939). N? Note: The documentation seems weak.

NOTE: The asterisk indicates the events which can be correctly defined as dry fogs either from their comparison with 1783, or because of the damage caused to the vegetation, or due to psychrometric measurements.

144

DARIO CAMUFFO AND SILVIA ENZI Table lb. Years during which the total number of foggy days was less than 10 during the summer in order to show how heterogeneous the fog distribution was in the various stations: Venice (1876-1925, Zanon, 1927); Milan (1835-1955, Santomauro, 1957); Rome (1825-1910, Eredia, 1911). The following table lists the anomalous year, in terms of number of foggy days (~ 10, indicated in brackets) which occurred during the summer VENICE: 1881 (19); 1887 (30); 1899 (14); 1901 (19); 1905 (69); 1906 (35); 1907 (34); 1909 (22); 1910 (11); 1911 (23); 1916 (18); 1919 (18); 1920 (13); 1923 (27); 1924 (33). MILAN: 1835 (11); 1836 (18); 1838 (10); 1839 (12); 1876 (20); 1877 (17); 1879 (17). ROME: 1827 (10); 1849 (11); 1861 (13); 1862 (10); 1868 (10); 1872 (12); 1873 (22); 1890 (11); 1903 (11).

so that the meteorological observations under examination were expressed in terms of dry fog. The events of 1824, 1866, 1869 (also described as being similar to the 1783 one), and those of 1883/4, 1886 were described in these terms. It should be noted also that the events of 1783 and 1812 (and probably those of 1824 too), are described as dry fogs in that they 'did not wet clothes' or other objects. The event of 1767 will also, probably, be included in the list, given its harmful effects on people's health. In order to complete the documentation, the most extensive information found in literature for the years in question is listed in Table I, even though sometimes the occurrence of the described phenomena may be casual. To show the temporal distribution in terms of amplitude, rather than frequency, the Tuckey-Hanning filter (Wei, 1990) Wn(k) = 0.54 + cos( 7lk/M) when Ikl "" M and Wn(k) = 0 when Ikl > M where M is the window width. In this paper M = 20 years, progressing wlth steps of 2 years. The results of such analysis for all the anomalous fogs reported in Table I is shown in Figure 2. It can be clearly seen that the phenomenon was definitely important between the end of the 1700s and the beginning of the 1800s. More than half the events occurring over the last five hundred years took place in the fifty years between 1775 and 1825.

4. Relationship to Volcanic Activity A modern reconstruction of the atmospheric effects of the 1783 volcanic episode has been supplied by Lamb (1970): A thick dry mist spread over the whole of Europe. It was registered for the first time in Copenhagen the 12 May, in France from the 6 June onwards and it was noticed in Italy from the 18 June. It even reached Syria and the Altais Mountains in central Asia from the first of July when it extended over North Africa and to Scandinavia. Notwithstanding the smell of sulphur that hung all over eastern Europe (with unpleasant effects on the eyes), and the documentation of the damage to plants in Holland between the 18 and 24 June, the mist in Europe, Asia and North America must have been in the upper part of the atmosphere because it was present for the whole of that summer, notwithstanding the direction of the low level winds, nor was it eliminated by the rain ... The mist over Europe was recorded until the end of September - beginning of October 1783.

This important episode has been carefully studied by Thordarson and Self

145


0.70 - r - - - - - - - - 0.60 0.50 0.40

FD 0.30 0.20 0.10 0.00 1400

1500

1700

1800

1900

year Fig. 2. Temporal distribution of the frequency F of the anomalous fogs reported in Table I (TuckeyHanning Filter).

(1993). The cause was the Laki (Skaftar Fires) fissure eruption in Iceland which began in May 1783 and it lasted for eight months, in association with the nearby Grfmsvotn volcano. They formed a series of explosive episodes which produced one of the largest basaltic lava flows in historic times. Fine ash, acidic aerosol droplets and volcanic gases emitted between the explosive phases formed a dense persistent dry fog that was transported and dispersed southward and eastward, causing illness to people and animals, damaging crops and vegetation, and causing the sun to appear weak and blood-red at sunrise and sunset. In past Italian chronicles and documents this event was frequently mentioned as a reference and a basis for comparison with other, successive eruptions. According to Lamb (1970) and Stothers and Rampino (1983), the dry fog which occurred after the eruption of Vesuvius in 1831 had similar effects, over a good part of Europe and North Africa, reaching Siberia and North America. The Italian data show a few foggy days and a persistent haze with weak sun, but, none so severe as in 1783. Sometimes, similar fogs appeared in opposite parts of the globe as a result of several local effects that were caused by contemporaneous minor eruptions of various volcanoes, and it is not always easy to distinguish between single contributions. The case of 1831, which had a global effect and not a local one, needs further study. The large scale effect was probably due to the contribution of other volcanoes that we know little, or nothing about. More often the volcanic fogs are geographically limited, given that aerosols and ashes can not remain in the troposphere for more than a few weeks. The purple sunsets and other photometeors, on the other hand, may be due either to material

146


suspended in the troposphere (with a short lifetime) or in the stratosphere (with a residence time of a few years), especially in the case of violent volcanic eruptions which may have occurred far from where the dry fog phenomenon was witnessed. In this case, the characteristic coloration assumed by the sun and other accompanying optic phenomena, would not necessarily indicate a dry fog of local origin and the events of 1462, 1465, 1511, 1810 and 1813 could be interpreted in this sense. Many other cases of dry fogs in Italy were found that could not be associated with the concomitant activity of the Icelandic volcanoes, but could only be associated with eruptions of the Mediterranean volcanoes. It is necessary to distinguish between the sporadic paroxysmic volcanic emissions and the more frequent, lasting and more modest ones. The former throw aerosols and ash into the stratosphere, with acid fallout on a global or hemispheric scale; the latter only eject material into the troposphere, thus producing local acidification and other effects. In fact, only four events (1734, 1783, 1815 and 1883), correspond to the acid fallout on the Greenland icecaps (Hammer et al., 1980). This acid fallout can be attributed to major explosive eruptions (Lanzarote in the Canaries, Laki in Iceland, Tambora and Krakatoa in Indonesia, respectively), although it is very unlikely that the last two were responsible for the formation of the Italian acid fogs. However, there is little doubt that the first two contributed in varying degrees to the action of the Mediterranean volcanoes, the Laki eruption probably being decisive. The comparison made with the deposits of ash in the Mediterranean sea (Cini Castagnoli et al., 1990; Bonino et al., 1993) shows a correspondence between dry fogs and ash deposits in 1682, 1794, 1822 and with minor deposits in 1374, 1735, 1780, 1805, 1883/4; however, several deposits were not associated with dry fogs. This is not surprising, as only a small part of volcanic activity, occurring in particular meteorological situations, leads to the formation of dry fogs. The environmental impact of the Italian volcanoes has been different in each case. The summits of the eruptive craters are: 3263 m (Etna), 1132 m (Monte Somma-Vesuvius), 1277 m (Vesuvius), 926 m (Stromboli), 499 m (Monte AriaVulcanello), 386 m (Vulcano), 123 m (Vulcanello). When contemplating the height reached by the plumes of material thrown into the air, it is necessary to take into account the violence of the eruption and the initial temperature, which determine the buoyancy of the plume in the atmosphere. For this reason, the summit explosions with violent emissions from the upper crater of Etna generally tend to follow a high level trajectory over Italy without any effect, except for some of the debris possibly falling on the Aspromonte mountains in Calabria (Fig. 1; for the Etna plume see Scorer, 1990, p. 186). The gases and aerosols emitted from the flanks of Etna as well as by the other lower volcanoes, especially Stromboli and Vulcano, may be trapped in the planetary boundary layer. Table 11 shows the activity of the Italian volcanoes which correspond to the events listed in Table I. From the former it can be clearly seen that all the dry fogs occurred at a time when a Stromboli was actively erupting, but the reverse

147

CLOUDS OF VOLCANIC AEROSOLS Table H. Years in which the dry fogs appeared and the corresponding volcanic activity (from Simkin et al., 1981); and the dendroc1imatic index ID calculated from the thickness h of the growth rings of trees (ID l : data from Bebber 1990; ID2 from Burro, 1987) Year 1374* 1462 1465 1499* 1511 1587* 1592* 1620 1648* 1682* 1689* 1690 1710* 1734 1735* 1740 1748 1763 1765 1767 1768 1775* 1780* 1783* 1785* 1786* 1791* 1794* 1802* 1803* 1805* 1807 1810 1812* 1813 1814* 1816* 1817 1819* 1821* 1824* 1831* 1866* 1869* 1883/84* 1886* 1890 1891

Etna

Vesuvius

Stromboli

Vulcano

Active Active

Active Active Active Active

Active Active Active

Active Active Active Active Active

Active Active Active Active Active Active

Active


Active

Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active

Active

Active Active

Active


Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active Active

Active Active

Active Active Active Active Active

Active Active Active Active Active Active Active Active Active

Active

IDl +0.224 +0.153 -0.060 +0.156 -0.305 -0.137 -0.133 -0.253 -0.090 +0.020 -0.552 -0.165 +0.159 -0.114 -0.170 -0.383 +0.279 +0.020 -0.268 +0.118 -0.067 +0.191 +0.471 -0.204 -0.216 -0.020 -0.106 -0.041 +0.233 -0.097 -0.011 +0.241 -0.153 -0.028 -0.615 +0.153 -0.052 +0.376 -0.228 -0.388 -0.097 +0.351 +0.034 +0.015 -0.154 -0.079 -0.004 +0.057

ID2

-0.039 -0.077 -0.276 +0.008 +0.144 -0.946 -0.759 +0.295 -0.145 -0.029 -0.423 -0.035 +0.295 -0.677 +0.352 -0.531 +0.410 +0.400 -0.712 -0.298 +0;528 -0.229 -0.830 +0.956 +0.092 +0.684 +0.437

148


is not true, in that Stromboli was more or less continuously active after 1558. If this is then added to the activity of Vesuvius, the correlation is valid for 2/3 of the cases, while it is much reduced when compared to the Etna and Vulcano eruptions, when the correlation is reduced to less than half. There were many concomitant eruptions, but nothing precise can be said, other than that before Stromboli became active again, the dry fogs were almost unknown, or at least were sporadic. In 1783 Stromboli, Vulcano and Vesuvius were active (Simkin et al., 1981), and the Stromboli eruption was particularly spectacular, so much so that Toaldo made a note in the margin of the daily Osservazioni Meteorologiche in the 'Specola' of Padua on the ll-th of March of that same year. Toaldo (1784) was very clear about his belief in the southern origin of the fog, at least with respect to Italy: We have considered this fog, that was high and dry, like a dust agitated by the violent shocks of the earth (referring to the earthquake in Calabria that accompanied the eruptions), or like the smoke of its internal fermentations, and we believe that it has been carried by winds to distant places from Calabria, such as over us.

From Toaldo's daily meteorological observations, it can be seen that in Padua the wind in the days preceding June was mainly in the 1st and 4th quadrant, mainly from the north and from the west, and successively, with a half frequency from the northeast, east, northwest which would favour the northwestern origin of the fog (Laki) rather than a southern one (Vesuvius, Stromboli and Vulcano). In the month of July, during which the fog persisted, the wind lay mainly between the 1st and 2nd half of the quadrant (between North and Southeast), confirming that the fog had been transported from the north.

5. Meteorological Situations Favouring the Formation of Dry Fogs Anomalous fogs in winter are rare, such as those found in 1817 and 1883/84, and in 1810 and 1866, that lasted until the summer. Fabri (1670), Boerhaave (1730) and Crivelli (1744) mentioned the acid rains which left caustic corpuscles on the vegetation in the summer. Most descriptions of the dry fogs refer to their presence at the end of spring and at the beginning of the summer but it is not pure coincidence, and not due to the fact that the wheat matures then, that makes it the most important indicator. There is a physical reason why dry fogs mainly develop at the beginning of the hot season in Italy. Due to the thermal inertia of the mass of sea water, the temperature of the sea becomes colder than that of the air for the whole April to August period, as shown by the maps of the average heat which is lost per unit time by the air contained in the layer 1000-600 hPa (i.e., above sea level up to approx. 4000 m) to warm the colder sea waters (Figure 3). In fact, the entire tract of Tyrrhenian Sea to the north of Sicily, which also includes the volcanoes Stromboli and Vulcano, is 0.6-0.8°C colder than the air in July, as shown in Figure 4. Once the Azores


149

Fig. 3. Average amount of heat (10- 7 cal g-1 S-1) lost per unit time from the atmosphericlayer 1000600 hPa (i.e. above sea level up to approx. 4000 m) to heat the colder sea water in July (redrawn after CNR-CENFAM and MDA-ITAV, 1964).

anticyclone has stabilized over the coldest part of the sea, the atmospheric pressure reaches a maximum locally, to the north of Sicily (Figure 5) which causes a descending flow over Stromboli, Vulcano and possibly Etna, and then a lateral divergence. Due to the absence of any wind inside the anticyclonic region and because of the stable atmosphere which has formed above the relatively cold waters, the low level emissions of the active volcanoes form a cloud of gases and aerosols that are then pushed towards the coast. The trajectories that the clouds of volcanic aerosols follow in the anticyclonic conditions are not well defined: they may cross Calabria on the northeast, or Sicily on the south, or even reach the Tyrrhenian coast moving northwards until the volcanic clouds are pushed inland by the sea breeze and then further transported by the valley breeze. The severe damage reported in the chronicles of northern Italy in the last centuries can thus be explained. In the spring months of March, April and May, the dominant winds are from the west and northwest while in the following three hot months of June, July and August they are from the northwest (Met. Office, 1962). In such a situation the Aspromonte mountains are particularly exposed to the acid emissions, in that they are about 80 km away in a northwest direction with respect to Stromboli, and at the same distance but in a north-northwest direction with respect to Vulcano. In

150


6 ____----...

Fig. 4. Distribution of thermal difference (6.T in tenths of 'c) between the temperature of the air and the sea surface in July. In the sea around Stromboli and Vulcano, the sea temperature is 0.60.8°C colder the air temperature (after Sutcliffe, 1960 in Reiter, 1971).

fact, the forests of Calabria are among the worst affected by acid rain in the the whole of Italy, especially the white fir in Serra San Bruno as well the Aspromonte forests in general (Gisotti, 1984; Camuffo, 1990).

6. Damage to Vegetation In the Complete Treatise on Agricultural Meteorology (Orlandini, 1853), the following description is found: Among the different species of fogs we can, for agricultural purposes, reduce them to two only. The damp fogs and the dry fogs. The damp fogs favour agriculture, as long as the plants are not near maturation. They bring, like the dew, humidity and substances in solution ... The dry fogs, form a haze through which the sun appears to be a bright red, not a real fog. These hazes ... spread over Europe in 1783, where they lasted for months.


Fig. 5. Average value of the atmospheric pressure (hP a) at sea level in the summer. The pressure reaches a local maximum to the north of Sicily, which includes Stromboli and Vulcano (after Metaxas, in Reiter, 1971 and 1975).

The damage to the vegetation was, in the case of the event of 1783, but also in others, considerable and described in detail: The dry fogs which can sometimes be observed, are accompanied by a great deal of evaporation followed by cold, and that produce in a brief time, the formation of dense masses of clouds and stormy rain. This excessive evaporation, takes up the humidity from plants, if such fogs occur at a time near their maturity; then the wheat can be seen to yellow and even become whitish, as if it had matured instantly; and if the wheat is still full of lactic juice, the grain becomes flaccid, and sometimes empties completely, conserving only the shell (Orlandini, 1853).

Different sources speak of the 'drying' of the ears and of the grains contained in them: such as for example, Fiandrini who reported quoting, with respect to the 1592 phenomenon, that: "a fog dried the grains, the ears ... " or, in 1663, that: "the wheat being more or less perfect in the ears, all of a sudden there was a fog that caused incredible damage in the whole of Romagna, by drying it and therefore the harvest was a very poor". The damage to the vegetation due to acid impact is evident and characteristic: the leaves and the grains were marked with a yellow colour and dried up. This effect was ingenuously thought to be due to the hypothetical, excessive evaporation. Toaldo (1781), described the damage to the harvest thus: When cutting the wheat many ears were found to be wholly or partly empty ... it was seen that the [fog] had spread slowly with the grain that is, narrow or empty ... ; [the fog] was seen to spread very slowly through the seeded fields [of wheat], which is capable of shrinking it, making the grain mature

152


before its time, that is to 'dry', or kill the immature plants. The straw has been dirtied by a yellow or black dust, called around our way 'melleo'. This explanation born of the observation and from the wholesome good sense of our farmers, seems to me more true than that ascribed to insects, plant parasites, and who knows what. It was common this year, as much in the low lands as in the high, as often in the Polesine as in the Vicenza and in the Treviso areas [in the Po Valley]; but in stretches, depending on the site, the exposure, the lack of ventilation, etc. It was estimated that a quarter of the harvest had been destroyed in the Polesine ...

The mechanism causing the damage to the vegetation in the cases studied here, does not seem to be due directly to the high concentration of gases which would otherwise have had lethal effects on the population. The most probable mechanism is that acid aerosols were deposited on the leaves of plants. These particles, being small, could stick to the surface for a long time, eliminating locally the waxy protective layer, thus leaving the leaf tissue exposed to aggressive agents, both physico-chemical and parasitic. The leaves of the plant were in fact yellowed with numerous punctiform lesions so they were easily attacked by parasites, as for example by the leaf rust described by Ramazzini (1718) or other varieties of it; see e.g. Vercellone (1721), the Varese Chronicle (1710), Toaldo (1781, 1787). One of the possible mechanisms for damage is the formation of calcium fluorsilicate on the surfaces of tephra which is derived from hydrofluoric acid above 600 QC. The particles with fluorsilicate once deposited on the leaves can cause burns (Bryant, 1991). The atmospheric fluorides can, in fact, cause necrosis at the edges of the leaves, drying them (Lorenzini, 1983; Lorenzini et al., 1987). These particular symptoms, which can easily be confused with damage caused by insufficient water, could be the reason why many of the descriptions attribute the damage to the plants being dried by the arid winds from the south. This damage was sometimes imply attributed to 'the wind': "the Sirocco (southeast wind), and still more the Libeccio (southwest wind), affect the plants, because of the illnesses they cause ... " (Thouvenel, 1797).

7. Damage to People and Animals The harmful effects to the health of the population and animals were documented on more than one occasion in 1783. The chroniclers did not have to hesitate to blame this on the dry jog, as Fajoni had done (18th century), affirming in his Diary: A phenomenon of prolonged and very dense fog, which completely hid the sun, and at night made the moon appear reddish and murky. This fog caused, moreover, many illnesses and putrid and acute fevers, so that many people died, and that year it proved impossible to dry the grain and the sorghum. In the summer there were whirlwinds and deadly bolts of lightning.

In his Diary, in the year 1783, Gennari informs us of the sudden death of many people identifying time as the first half of August until, that is, the intense rain eliminated the fog: "This month, at least until half way through it, relentless diseases raged and many people died within a few days".


153

The same diary also documented the death of animals in the stricken zone in September. It is possible that the cause of the phenomenon is to be searched for among those tentatively proposed at the time, but it is still more probable that the cause was due to an epidemic resulting from the ingestion of pasture contaminated by volcanic aerosols. The same author suggests the hypothesis that the cause of the illness was closely connected to the fodder, in that animals fed on 'good hay' were not affected: From the first days of the said month [September] an illness began to be manifest in the cattle that was thought to be contagious and originating from beef transported from Dalmatia .... All the cattle attacked by the illness died ... In the mean time, the illness attacked other country villages ... which added strength those who attributed the origin of the illness to the Dalmatian cattle. It is more probable however, that it started from the bad feed that the whole of the last winter which the said animals had eaten given that the farmers compensated for the lack of hay due to the preceding drought, by feeding them on leaves from trees and especially nut trees. Then, when the damp and always foggy spring came, the hungry cattle were sent to pasture on fresh grass on which they gorged themselves, being greedy and [the grass] ever so tender, their insides were affected by a malevolent disorder that then developed into the current illness. It was observed that the cattle which had been fed on good hay, have not, up till now, been affected by the bad influence.

8. Increased Frequency of Storms It is known that the particles emitted into the atmosphere from an urban pollution

increases precipitation locally, especially precipitation of a stormy nature (e.g. Barry and Chorley, 1978). The elevated presence in the atmosphere of hygroscopic particles of volcanic origin that act as condensation nuclei typically causes violent storms, especially in the summer when the ascending thermoconvective currents are stronger. Evidence of storms and hailstorms generally follow reports of dry fogs. The same intuition, at least on the empiric level, had already been formulated in the 18th century, when scholars connected the dry fogs and the storms: "the abbot Toaldo assigned the cause of the very copious vapours that were released from the viscera of the earth to the earthquakes in Calabria and therefore again resulted [in causing] the greater part of the lightning that we have had" Gennari reports. In 1794 Toaldo repeated The frequency of lightening and also of the storms in this year of 1794 was almost the same as 1783. The one and the other were accompanied by the dry fog that obscured the sky and obfuscated the stars for months. The one and the other combined to the fermentations, concussions and eruptions of the earth: together with this reigned the desolation of the earthquakes in Calabria; with this other than the earthquakes, the prodigious eruption of Vesuvius which, after the [Roman Emperor] Titus one [i.e. 79 A.D.]' had no equal. It is likely that in such cases a quantity of igneous vapours, elastic fluids, dense air, in particular electric fir, and inflammable air which produce storms and lightning, while the dense vapours obscure the sky.

Again Gennari describes the drought which occurred in 1783 and the continuous storms, very often accompanied by hailstones, that characterized the period:

154


Along with a long and constant drought we have had days of copious rain and yesterday, that was the 30 [of May), towards the 20 hour [hours computed from the twilight, according the so called 'Italian style', i.e. 4 p.m. Western Europe Time (WET)), there was a rather dark storm and an impetuous wind that brought down a good piece of the wall of the Teatini fathers, adjacent to the cottages of the Corner along the stream of S. Sophia. and pulled up a tree or two. Again the hail fell in the villages of Saonara, Legnaro, Limena and elsewhere. These continuous heavy rains have flooded the valleys and lowlands of the territory where, while waiting for the preceding dry season, there had been an abundant sowing; of maize and in the succulent fields the wheat has been flattened and, moreover, stopped the hoeing of the Indian wheat already come to fruit ....

In August, after having dealt with the unusual meteorological trend of the season, Gennari again reports news about persistent dry fog and the frequency of the bolts of lightning, telling us that these were widespread in Italy and on the other side of the Alps: Along with some very hot days, today at the 20 hour [Le. 4 p.m. WET) a threatening storm arose that then finished in heavy rain which was gold for the thirsty countryside. But as this year there has never been a storm of thunder and lightning without bolts, so again today there were two bolts of lightning; A lot of rain fell yesterday and a copious hailstorm spread ... not only tempered the past summer heat but refreshed and cooled the air so much that we were forced to wear a cloak of cloth. Such passing from hot to cold is dangerous for human health is frequent in our climate [this year shall be memorable for the great couple of bolts of lightning that exploded not only in Italy but in the whole of Europe ... Also this month [Le. August), now terminated, has always been foggy, that not even one morning was the sun seen rising as bright as usual, the horizon having always been hidden by fog and by dense vapours and withal, it did not rain even once. And we read that this has happened again in other parts of Italy and beyond the mountains and seas as far as Aleppo [Syria).

9. Correlation with Tree-rings Given that the dry fogs provoke damage to the harvests, it is reasonable to suppose that they might leave signs on the growth rings of trees, even though Bradley and Jones (1992) suggest extreme prudence: not all volcanic emissions have caused narrow rings, and not all narrow rings are due to volcanic emissions. In fact, the climate forces narrow rings during a dry and/or cold year. The dendroclimatic index ID = 2(h n - hn-1)/(hn- 1 + h n), where hn and h n- 1 refer respectively to the thickness of the ring of the year (n) of the event and that of the preceding year (n - 1) was introduced to put into evidence the effects, if any, of the dry fogs on the tree growth. Obviously, when a value of ID < 0 is seen, it signifies a reduction in the growth resulting from some stress to which the plant has been subjected, at least with reference to the conditions of the preceding year; ID < 0 signifies an increase in the growth. Two tree ring series were used, one by Bebber (1990) and one by Burro (1987). Both refer to trees in northern Italy. The former is the longer one (starting in 781 A.D.) and is composed of samples of Larix decidua mill. coming not only from the the Po Valley, but also many mountain valleys in the Alps where the masses of air, and therefore the dry fogs, penetrate with greater difficulty. The latter is still of Larix decidua mill., but shorter (starting in 1564), with trees of the Po Valley. The results are shown in


155

Table n, and the conclusions are quite similar. It can be clearly seen that during the years when there were anomalous fogs (indicated by an asterisk), the ID values are negative with a frequency that is almost double (19: 11) those of the values ID > 0, underscoring the weak dependence between the dry fogs and stress to the trees. This is not surprising, considering that the majority of the dry fogs occurred after the spring, which is the period of maximum plant growth and that climatic factors would leave a greater sign on the growth rings of trees than would any brief exposure to acid aerosols, unlike the effect these had on herbaceous plants such as cereals, wheat or maize. Only in some cases of particular gravity does the ID index become strongly negative: for the years 1689, 1783 and 1794.

10. Clouds of Volcanic Aerosols or Saharan Dust? In the past, the presence of a hot wind of an apparently African origin, the red coloration of the sky, the scarce visibility and the damage to leaves and grain, led to the supposition that a cloud of dust had been transported from the deserts of north Africa, rather than a cloud of volcanic aerosols. For example, Orlandini (1853) wrote: "These hazes which reflect the light in red accompany the 'Harmattan', a wind from the African continent". To be precise, in Italy, one should think of the Sirocco (which in Italy comes from the southeast), rather than the Harmattan (which does not arrive in Italy and in Africa blows from the northeast or east). However, the Sirocco, even though it is, initially, very hot and dry, by the time it arrives at the Po Valley latitudes, it has been sufficiently cooled to become humid. Moreover, from the dynamic climatology of the Po Valley it can be said that the Sirocco is responsible for precipitations which contain red saharan dust, but it does not cause persistent fogs. The Sirocco is, however, necessary for the transport of volcanic aerosols from Sicily (Stromboli, Vulcano and Etna) and Campania (Vesuvius). Finally, the Saharan dusts are not foul smelling like the dry fogs and cause no halm to the vegetation, unlike the acid aerosols. The effects of these latter are similar, as has been said, to the drying of the edges of the leaves due to the lack of water. Possible doubts can arise about the effective nature of the reddish color that is often witnessed: whether it were an intrinsic characteristic of the haze; or whether it was the yellowish colour seen at dusk due to the Saharan sand suspended in the Sirocco wind,; or whether this is a color deriving from the sky becoming purple (at dawn and dusk) as a result of the scattering caused by aerosols present in the upper troposphere or in the stratosphere. In fact, excluding the night when the colors could not be seen, a haze is thicker at dawn and at sunset, just as the sky is tinted red anyway, while it is much weaker in the middle of the day. The hypothesis of mistaken purple sunsets caused by saharan dust for dry fogs must, however, be discarded on the basis of Toaldo's daily observations. In his register, for the month of June 1883, the following annotation is found: "Day 18: in the

156


afternoon that famous dry fog began to appear that has pervaded the whole of Europe and about which much has been written", and for some of the following days 'red sun', 'bloody', and 'murky'. There is no mention of any purple sunsets in the preceding period, nor are there any other observations about the color of the fog, other than that which it assumes when it is against the light of the sun, which appears, moreover, convincing.

11. Conclusions Dry fogs are malodorous clouds of gases and volcanic aerosols, emitted above all from stromboli, and then by Vulcano, Vesuvius and the flanks of Etna. These gases and aerosols may be entrapped in the stable layer which forms when the waters of the Tyrrhenian Sea are colder than the air, in the spring and summer periods, and there is an anticyclonic area centered north of Sicily. Under these conditions, the clouds of volcanic aerosols may reach the coast and cause damage to the vegetation and other effects. In addition to the sporadic cases in which extended volcanic fogs or clouds are formed, continuous volcanic pollution occurs. The Aspromonte mountains which are only 80 km away from Stromboli and Vulcano, in the direction of the dominant winds, are particularly exposed to the plumes of volcanic gases and aerosols. The damage to the vegetation is due, above all, to the action of acid particles which stick to the leaves for a long time, thus removing the protective wax and provoking necrosis, or leaving them without any defense against aggressive elements and parasites. It is not always easy to recognize a dry fog that occurred centuries ago because, especially before 1783, as they were unfamiliar, and could be taken for haze in the dissipation phase (when the level of relative humidity had been lowered and they were no longer 'wet'), and it is often necessary to base the facts on summary descriptions of common witnesses. Mention of damage to the harvest of wheat and maize was an extremely useful indication in determining the nature of the phenomenon. However, this poses great limitations when trying to verify the nature of fogs and there is a very real risk of excluding those older acid fogs which did not occur in the summer, although this is the period of the maximum occurrence. From the dendrochronological investigation however, no evidence emerged of any serious impact on the growth of trees, except for a few cases of particular seriousness. Some unusual summer fogs occurring in the mid-1700s have been mentioned, but as the observers were more interested in the purely meteorological aspect of the phenomenon rather than its ecological effects, some questions remain unanswered about that interesting period. In the fifty years between the end of 1700 and the beginning of 1800, the haze phenomenon due to volcanic aerosols became so common, and the damage to the harvests so great, that it was even reported in a treatise of meteorology applied


157

to the agriculture, alongside the common hydrometeors which are today called fogs, and which were then called damp fogs in order to distinguish them from dry fogs. It is difficult to attribute a direct relationship between cause and effect, capable of identifying the individual volcano that has determined, each time, the occurrence of dry fogs. It would seem much more reasonable to note that the phenomenon became frequent only after Stromboli became active once again. However, given the closeness and the alignment of the Italian volcanoes with respect to the Sirocco wind, their emissions could reach northern Italy mixed altogether. As volcanoes are continuous sources (for certain periods), it is possible that the most dramatic effects were obtained when a considerable quantity of emissions were concentrated in the atmosphere near the sources under conditions of calm wind and atmospheric stability and that the following transport occurred under low atmospheric diffusive potential. The daily measurements of the wind direction at Padua in June and July of 1983 suggest that it is likely that the fog on that particular occasion was due to the Icelandic volcano Laki, while the other events were more likely due to the nearby Mediterranean volcanoes, and that Stromboli was, apparently, of primary importance. It being the case that in Northern and Central Italy the phenomenon could, in general, be described in terms of dry haze associated with southern winds, the scholars of the time supposed that desert dust transported by the Sirocco was what they were dealing with. From a climatic point of view (e.g. with the Sirocco, fog does not appear in the Po Valley), and from the foul smell and the analysis of the negative effects that these fogs had on people, animals and vegetation, it is possible to state that the phenomenon was due to the transport of clouds of aerosols of a volcanic origin and not saharan dust. Given that the formation of the clouds of volcanic aerosols is conditioned on the presence, at the same time, of some other factors as happens typically in the spring-summer period, it is to be expected that this phenomenon continues today, causing damage to the most exposed population, vegetation and monuments.

Acknowledgments This study has been carried out within the CNR Strategic Programme 'Climate, Environment and the Territory of the Southern Italy' under the co-ordination of the European Science Foundation and the environmental programme STEP of the Commission of the European Community (contract: CT 90-0107). Special thanks are due to Dr. S. Self, Department of Geology and Geophysics Volcanology Geochemistry and Petrology, Hawaii University, for many useful suggestions and a careful review of this paper. Thanks are due also to Dr. R. Frazzetta, CNR, International Institute of Volcanology (Catania) for useful documentation.

158


Note: D. Camuffo, a Physicist and S. Enzi, Historian, both contributed within their specific competences to this interdisciplinary study.

References Modern Papers Barry, R. G. and Chorley, R. J,: 1978, Atmosphere, Weather and Climate, Methuen and Co., London, 432 pp. Bebber, A. E.: 1990, Una cronologia del larice (Larix decidua mill.) delle Alpi orientali italiane, Dendrochronologia 8, 119-139. Bonacini, T.: 1939, Meteore ottiche registrate all'Osservatorio di Modena nel periodo 1828-1935. Pubblicazioni del R. Osservatorio Geofisico di Modena, n. 59, Soliani, Modena, 63 pp. Bonino, G., Cini Castagnoli, G., Callegari, E. and Zhu, G.M.: 1993, Radiometric and Tephroanalysis Dating of Recent Ionian Sea Cores, Nuovo Cimento 16C(2), 155-162. Bradley, R. S. and Jones, P. D.: 1992, Records of explosive volcanic eruptions over the last 500 years, in R. S. Bradley and P. D. Jones (eds.), Climate since A.D. 1500, Routledge, London, pp. 606622. Bryant, E. A.: 1991, Natural Hazards, Cambridge University Press, Cambridge. Burro, M.: 1987, Analisi di strutture lignee ritrovate sulla riva del fiume Brenta, Dendrochronologia 5,105-109. Camuffo, D.: 1990, Acidic Precipitation in Italy, in A. H. M. Bresser and W. Salomons (eds.), Acidic Precipitation - Volume 5: International Overview and Assessment, Springer-Verlag, New York, pp. 229-265. Camuffo, D.: 1992, Acid rain and deterioration of monuments: how old is the phenomenon? Atmospheric Environment 26B(2), 241-247. Cini Castagnoli, G., Bonino, G., Caprioglio, F., Provenzale, A., Serio, M., and Zhu G. M.: 1990, The carbonate profile of two recent Ionian Sea cores: Evidence that the sedimentation rate is constant over the last millennia, Geophys. Res. Lett. 17(11), 1937-1940. Chester, D. K., Duncan, A. M., Guest, J. E., and Kilburn, C. R. J.: 1985, Mount Etna, Chapman and Hall, London, 404 pp. CNR-CENFAM and MDA-ITAV: 1964, Research Work on the Project Cyclone Development in the Lee of the Alps, 4th General Report, STR No. 6, CNR-CENFAM, Rome. Corliss, W. R.: 1983a, Tornados, dark days, anomalous precipitation and related weather phenomena, Sourcebook Project, Glen Arm. Corliss, W.R.: 1983b, Earthquakes, tides, unidentified sounds and related phenomena, Sourcebook Project, Glen Arm. Gisotti, G.: 1984, Potenziali effetti delle piogge acide sui patrimonio agricoio e boschivo, in Precipitazioni acide in Italia - Problemi ed effetti, Progetto Finalizzato Energetica, SC-12, CNR-ENEA, Rome, pp. 215-244. Eredia, F.: 1911, Il clima di Roma, Bertero, Rome. Hammer, C. U.: 1977, Past volcanism revealed by Greenland ice sheet impurities, Nature 270,482486. Hammer, C. U., Clausen, H. B., and Dansgaard, W.: 1980, Greenland ice sheet evidence of postglacial volcanism and its climatic impact, Nature 288, 230-235. Lamb, H. H.: 1970, Volcanic dust in atmosphere, in Phil. Trans. Roy. Soc., A, 266 n. 1178,25-533. Lorenzini, G.: 1983, Le piante e l'inquinamento dell'aria, Edagricole, Bologna, 355 pp. Lorenzini, G., Panattoni, A., and Guidi, L.: 1987, Ricerche sugli effetti fitotossici dei fluoruri atmosferici nei dintomi di una sorgente industriale. Informatore Fitopatologico 37(3), 41-48. Meteorological Office: 1962, Weather in the Mediterranean, Vol. I: General Meteorology, H.MoS.O. London, 199 pp. Priestley, M. B.: 1981, Spectral Analysis and Time Series, Academic Press, London, 890 pp. Reiter, E. R.: 1971, Digest of Selected Weather Problems of the Mediterranean, NAVWEARSCHFAC TP. No. 9-71, Navy Research Facility, Norfolk, Va.


159

Reiter, E. R.: 1975, Handbook for Forecasters in the Mediterranean, ENVPREDSCHFAC TP. No. 5-75, Navy Research Facility, Naval Postgraduate School, Montrey, Ca. Romano, R. and Sturiale, c.: 1982, The historical eruptions of Mt. Etna, Mem. Soc. Geol. It. 23,7579. Salmelli, D.: 1986, L'alluvione e il freddo: il1705 e i11709, in R. Finzi (ed.), Le meteore e ilfrumento, Il Mulino, Bologna, 387 pp. Santomauro, L.: 1957, Lineamenti climatici di Milano, Quaderni della dtta di Milano, Milano, 251 pp. Simkin, T., Siebert, L., McClelland, L., Bridge, D., Newhall, c., and Latter, J. H.: 1981, Volcanoes of the World, Smithsonian Institution, Hutchinson Ross, Stroudsbourg (USA), 232 pp. Stothers, R. B. and Rampino, M. R.: 1983, Volcanic eruptions in the Mediterranean before A.D. 630 from written and archeological sources, 1. Geophys. Res. 88(B8), 6357-6371. Sutc1iffe, R. c.: 1960, Depressions, Fronts and Air Masses Modifications in the Mediterranean, UNESCO/WMO Seminar on Mediterranean Synoptic Meteorology, Rome, 1958. Thodarson, Th. and Self, S.: 1993, The Laki (Skaftar Fires) and Grimsv6tn eruptions in 1783-1785, Bull. Volcanol. 55, 233-263. Wei, W. W. S.: 1990, Time Series Analysis, Addison-Wesley, Redwood City, Ca., 478 pp. Zanon, F. S.: 1927, Riassunti mensili e annuali delle osservazioni meteorologiche del cinquantennio 1875-1925, Ferrari, Venice, pp. 1380-1432.

Documentary Sources Anonimous - Filiasi? 1791, Saggio sapra in Veneti primi, Savioni, Venice. Battistella, A.: 1930, Il secolo XVI in Friuli nei riguardi climatici, igienici e meteorologid, in Atti della Accademia di Udine, 8-9, s. V, v. IX. Bertirossi Busatta, F.: 1807, Relazione meteorologica dell'anno 1807, in Giornale Astrometeorologico per l'anno 1809, Andreola, Venice. Bertirossi Busatta, F.: 1812, Relazione meteorologica dell'anno 1810, in Giornale Astrometeorologico per l'anno 1812, Andreola, Venice. Bertirossi, Busatta, F.: 1917, Relazione meteorologica, in Giornale Astrometeorologico per l'anno 1817, Alvisopoli, Venice. Boerhaave, H. 1730, Elementa Chemie, Vo!. 1, Coleti, Venice. Bollettino dell'Osservatorio della Regia Universita di Torino, aa. 1881-1888 (15th-XXII). Bonoli, P.: 1661, Istoria della citta di Forli, in Biblioteca Classense F.A.3.4. Mn. 2. Bonucci, c.: 1845, Vicinanze dell a Metropoli, in AA.VV.: Napoli e i luoghi celebri delle sue vicinanze, Nobile, Naples. Botta, C.: 1834, Storia d'Italia continuata da quella del Guicciardini sino al 1789, t. 15th, Elvetica, Capolago. Chiminello, V.: 1804, Relazione dell'anno 1802, in Giornale Astrometeorologico per l'anno 1804, Andreola, Venice. Chiminello, V.: 1805, Relazione meteorologica dell'anno 1803, in Giornale Astrometeorologico per l'anno 1804, Andreola, Venice. Chiminello, V.: 1806, Fenomeni precedenti, contemporanei e seguenti al terremoto napolitano dei 26 Luglio 1805 comunicati all'autore dai celebri Monsignor Giovene, e dal Sig. Cassella R. Astronomo di Napoli, in Giornale Astrometeorologico per l'anno 1806, Andreola, Venice. Conti, C.: 1833, Relazione meteorologica dell'anno 1831, in Giornale Astrometeorologico per l'anno 1833, Stamperia del Seminario, Padua. Crivelli, G.: 1744, Elementi di Fisica, Occhi, Venice. Denza, P.: 1869, La caligine atmosferica, Bullettino Meteorologico dell'Osservatorio del R. Collegio Carlo Alberto in Moncalieri 10, 110. Pabri, H.: 1670, Physica, id est Scientia Rerum Corporearum, Vo!. 3, Anisson, Lyon. Pajoni, A.: 18th century, Diario Sermidese, (unpublished manuscript of the Zanardi family), in G. Mantovani, Il territorio sermidese e limitrofi, pp. 173-190, Cattaneo Gaffuri and Gatti, Bergamo 1886. Fiandrini, B.: 18th century, Annali Ravennati, t. I, Ms. Biblioteca Classense mob. 3.4. C.

160


Filiasi, J.: 1815, Relazione Meteorologica che incomincia dal Novembre 1813 e termina col Dicembre 1814, in Giornale Astrometeorologico per l'anno 1815, Andreola, Venice. Filiasi, J.: 1816, Relazione del Sig. co. Jacopo Filiasi dal primo Gennajo 1815 8ino a tutto Agosto dell'anno stesso, in Giornale Astrometeorologico per l'anno 1816, Stamperia del Seminario, Padua. Filiasi, J.: 1818, Relazione dal12 Settembre 1816 ai 20 detto 1817, in Giornale Astrometeorologico per l'anno 1818, Stamperia del Seminario, Padua. Filiasi, J.: 1821, Relazione meteorologica che comincia dal 15 Settembre 1820 e termina coi primi di Settembre 1821, in Giornale Astrometeorologica per l"anno 1822, Stamperia del Seminario, Padua. Filiasi, J.: 1824, Relazione meteorologica che comincia dal Settembre 1823 e termina con Agosto 1824, in Giornale Astrometeorologico per l'anno 1825, Stamperia del Seminaro, Padua. Filiasi, J.: 1828, Osservazioni sopra le vicende annuali di Venezia e paesi circonvicini, Andreola, Venice. Gatari, A.: 15th century, Cronaca Carrarese, in L. A. Muratori (ed.), RIS, 17th, I, Lapi, Citta di Castello 1931. Gennari, G. 1739-1800, Notizie giornaliere di quanto avvenne in Padova, L. Olivato (ed.), Rebellato, Padua, 1928. Ghirardacci, C.: 16th century, Abbozzo dell'historia di Bologna di fra Cherubino Gharardacci, Ms. 2012, b. 1, Biblioteca Universitaria di Bologna. [The opera omnia by Ghirardacci was published by A. Sorbelli (ed.), Historia de Bologna, in L. A. Muratori (ed.), Rerum Italicarum Scriptores, Zanichelli, Bologna 1933]. Infessura, S.: 16th century, Della citta di Roma, in Istituto Storico Italiano, O. Tommasini (ed.), Fonti per la Storia d'Italia, Rome, 1890. Locati, O. 1564, Chronaca delle origini di Piacenza, Ms. Biblioteca Estense A. 15th L. 26. Marangoni, C.: 1884-5, Due memorie sui crepuscoli rossi, in Rivista Scientifico Industriale, Arte delle Stampa, Florence. Morgagni, G. B.: 18th century, Osservazioni Meteorologiche, aa. 1740-1768, Padua. Nadi, G.: 16th century, Diario di Gasparo Nadi, Ms. Biblioteca Comunale, Bologna 17/k.II.52. Orlandini, O. 1853, Trattato completo di Meteorologia Agricola, Garinei, Florence. Pasolini, S.: 1701, Lustri Ravennati, 1. 16th, 1. Ill, Monti, Bologna. Penada, J.: 1815, Quadro ristretto delle meteorologiche vicende occorse in tutto l'anno 1813, in Giornale Astrometeorologico per l'anno 1815, Andreola, Venice. Penada, J.: 1816, Quadro generale delle meteorologiche vicende occorse in tutto l'anno 1814, in Giornale Astrometeorologico per l'anno 1816, Stamperia del Seminario, Padua. Penada, J. 1818, Meteorologia dell'anno 1816, in Giornale Astrometeorologico per l'anno 1818, Stamperia del Seminario, Padua. Penada, J. 1821, Relazione meteorologica, in Giornale Astrometeorologico per l'anno 1819, Stamperia del Seminario, Padua. Penada, J.: 1822, Quadro meteorologico dell'anno 1821, in Giornale Astrometeorologico per l'anno 1823, Stamperia del Seminario, Padua. Penada, J.: 1823, Relazione meteorologica dell'anno 1821, in Giornale Astrometeorologico per l'anno 1824, Stamperia del Seminario, Padua. Ramazzini, B.: 1718, Constitutiones epidemicas annorum 1690, 1691, 1692, 1693, 1694, Conzatti, Padua. Schiavina, G.: 17th century, Annales Alexandrini, in Historiae Patriae Monumentae, t. XI, Scriptores t. IV, Torino 1863. Secchi, A.: 1866, La caligine atmosferica e sua origine, in: Bullettino Meteorologico dell'Osservatorio del Collegio Romano, 5, 5, p. 17. Spaccini, G. B.: 17th century, Cronaca della citta di Modena, v. IV, Ms. Archivio Storico Comunale, Modena. Tacchini, P.: 1884, Sui crepuscoli del Novembre e Dicembre 1883 e 1884, Nuova Antologia 18(2), 529-547. ThouveneI, P.: 1797, Traite sur le climat de l'Italie, Giulari, Verona. Toaldo, G.: 1766-1804, Note manoscritte a margine deIla "Osservazioni Meteorologiche", Non numbered sheets, Bib!. della Specola, Padua. Toaldo, G.: 1775, Discorso sopra l'anno 1774letto nell'Accademia Agraria di Padova iI d! 4 Gennaro 1775, in Giornale Astrometeorologico per l'anno 1775, BettinelIi, Venice. Toaldo, G.: 1781, Altre osservazioni sopra l'anno 1780, in Giornale Astrometeorologico per !'anno 1781, Storti, Venice.


161

Toaldo, G.: 1784, Dei principali accidenti dell'anno 1783, in Giornale Astrometeorologico per l'anno 1784, Storti, Venice. Toaldo, G.: 1784, Punti di luna, ed aspetti, in Giornale Astrometeorologico per l'anno 1784, Storti, Venice. Toaldo, G.: 1785, Punti unari ed aspetti principali, in Giornale Astrometeorologico per l'anno 1785, Storti, Venice. Toaldo, G.: 1787, Breve descrizione dell'anno 1785; Dell'anno 1786, in Giornale Astrometeorologico per l'anno 1787, Storti, Venice. Toaldo, G.: 1789, De1la qualita fisica delle plaghe. Saggi Scientifici e Letterari del/'Accademia di Padova 2, 121-142. Toaldo, G.: 1793, Pioggie dell'anno 1791 in vari luoghi d'Italia, in Giornale Astrometeorologico per l'anno 1793, Storti, Venice. Toaldo, G.: 1795, Dei conduttori, e parafulmini, in Giornale Astrometeorologico per l'anno 1795, Storti, Venice. Toaldo, G.: 1797, Della vera influenza degli astri sulle stagioni e mutazioni di tempo, Bettinelli, Padua. (Ser) Tommaso da Silvetro: 16th century, Diario, in L. A. Muratori (ed.), Rerum Italicarum Scriptores, t. 15th, p. V, v. n, cur. L. Fumi, Zanichelli, Bologna 1922-1929. Tummulillis, A.: 15th century, Notabilia Temporum, in Istituto Storico Italiano, C. Corvisieri (ed.), Fonti per la Storia d'Italia, Roma 1890. Valatelli, A.: 1803, Della topografiafisico-medica di Venezia, Andreola, Venice. Venerio, G.: 1851, Osservazioni meteorologiche fatte in Udine e nel Friuli per il quarantennio 1803-1842, Vendrame, Udine. Zantedeschi, F.: 1866, Dei caratteri astro-meteorologici del trimestre di Gennaio, Febbraio e Marzo 1866, Atti lstituto Veneto Lettere Scienze e Arti, 12(3), 15-73.