Results of methane and carbon monoxide total ...

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Period of 1999-2002 has a significant decline of CH4 TCA for ... Since 1991, ground-based spectroscopic observations of the gases total column amounts have ...
Results of methane and carbon monoxide total column amount measurements near St. Petersburg (Russia) Maria Makarova*, Yuriy Timofeyev, Anatoly Poberovski, Tatiana Aparina, Irina Yakovitskaya Laboratory of Remote Sensing, Dept. of Atmospheric Physics, Research Institute of Physics, St. Petersburg State University, 1 Ulyanovskaya str., St. Petersburg, 198504, Russia ABSTRACT Methane (CH4) and carbon monoxide (CO) total column amounts (TCAs) measured at the Research Institute of Physics of St. Petersburg State University (Russia) were used for: 1. study of temporal variability of CH4 and CO; 2. identification of source regions of CO and CH4 using trajectory analysis. CH4 and CO showed distinct annual cycle with the amplitude of about 3% and 25% respectively. Period of 1999-2002 has a significant decline of CH4 TCA for the St. Petersburg region. The suggested reason is hot and dry summers of 1998-2002. October 1998 - March 1999 is characterized by the strong irregular disturbances of CO TCA. Growth rates of CO TCA have changed at this period from (3.5±2.3)%/yr. (for 1995-1998) up to (-2.1±1.5)%/yr. (for 1999-2002). Enhanced CO and CH4 TCA levels are observed for air masses originated from the sectors of the North Russia, continental Russia and the Eurasia. Europe can be classified as moderately polluted territory. Clean air comes from the Baltic Sea, Arctic Ocean and Scandinavia. Distribution of CO pollution levels over sectors repeats qualitatively situation for CH4. Keywords: ground-based IR spectroscopic measurements, greenhouse gases, methane, carbon monoxide, pollution in the troposphere, remote sensing.

1. INTRODUCTION Since 1991, ground-based spectroscopic observations of the gases total column amounts have been carried out near St. Petersburg, Russia. The major aim of such monitoring is to study temporal variability of atmospheric trace gases – a key to correct modeling of the Earth’s climate processes. Measurement site is situated in 35 km south-westward the St. Petersburg (59.88o N, 29.83o E), with elevation of about 20 m above sea level. Solar infrared spectrometer (SIRS) performs observations of direct solar IR radiation spectra in range of 3.15-4.55 µm with spectral resolution 0.3 -1.0 cm1 [1].

2. SPECTROSCOPIC MEASUREMENTS METHODOLOGY Solar radiation recorded by spectrometer can be written as:

U (ν i ) = ∫ F (ν ) ⋅ A(ν −ν i ) ⋅ exp[− τ i (n( z ))]dν + δU i

(1)

∆ν

where F (ν) - function depends on spectrometer parameters, nonselective attenuation of the atmosphere and sun radiation at the top of the atmosphere; A (ν- νi) - instrumental function of spectrometer; δUi - measurement noise; n(z) – vertical distribution of gas concentration; τi(n(z)) - optical thickness. *

[email protected]

The TCA (w) of the gas (have to be determined) can be parameterized as: H

H

z0

z0

w ≡ ∫ n( z )dz = c ∫ n ( z )dz = cw

(2)

where n (z ) – assumed vertical distribution of gas concentration; w - gas total column amount corresponding to n (z ) vertical distribution; τ - optical thickness for w ; c – unknown parameter. Using (1), (2) and assumption of F (ν) linearity on the spectral intervals:

U (ν i ) =

∫ν F (a, b,ν ) ⋅ A(ν − ν ) ⋅ exp( −cτ )dν

(3).

i



The solution of equation (3) is consists in determination of parameters c, a, b by optimal estimation method. Original software for gas TCA retrievals from IR spectra was developed at the Laboratory. Total random errors of gases TCA have been estimated on the basis of numerical investigations [2]. Spectral regions, major absorbing gases (included into calculations) and corresponding TCA random errors are indicated in the Table1. Table1. TCA random errors, spectral regions and major absorbing gases for chosen spectral regions. Measured gas

Spectral region, cm-1

СН4 H2O СО

2890 – 2910

Major absorbing gases СН4, Н2О

2140 – 2180

СО, Н2О, N2О

TCA random error, % 4 6 5

4. METHANE TCA TIME SERIES ANALYSIS 1. Daily mean values of CH4 TCA for the period of 1991-2003 are given in Fig.1. Minimal (3.20*1019 mol/cm2) and maximal (4.08*1019 mol/cm2) values of CH4 TCA were observed in August 2002 and December 2001 respectively. We suppose that hot and dry summer of 2002 (for Northwest Russia) was the main reason of low CH4 TCA values. Wetlands and marshes (powerful sources of CH4 emission in the region) have been dried up during 1999-2002. Average CH4 TCA over all measurement period is equal to 3.54*1019 mol/cm2. 2. Difference (d) between maximal and minimal values (Fig. 2) observed for each year was used as a measure of CH4 TCA variability. To the decrease of CH4 lifetime in the atmosphere can be attributed increase of d value (see Fig.2) throughout the measurement period [3]. 3. Mean annual cycle of CH4 TCA obtained for St. Petersburg over all measurement period is given in Fig. 3a. Solid line in Fig. 3a is a polynomial approximation of CH4 annual cycle. Error bars in Fig. 3a have the sense of CH4 TCA interannual variability. It is greater during autumn-winter due to increase of natural gas utilization and relatively small number of measurement days. Mean annual cycle of CH4 TCA has maximum in the November-December and minimum during June-August. Its amplitude is of about 4%. For example, annual cycles for 2002, 2001, 1995, 1999, 2000 years are illustrated in Fig. 3(b) respectively. Annual cycle for each year can differ essentially from the mean one (see Fig. 3 b for 1995). Annual cycles for 1999, 2001 and 2002 are reasonably similar to the mean cycle but 2002 has greater amplitude. Such differences are caused by the variability of methane sources and sinks.

CH4 TCA, *1019 mol/cm2

4.2 4 3.8 3.6 3.4 3.2 3 1991

1993

1995

1997 year

1999

2001

2003

Figure1. Daily mean values of CH4 TCA near St. Petersburg.

25

d, %

20 15 10 5 0 1992

1994

1996

1998

2000

2002

Figure 2. Difference (d, %) between maximal and minimal values of CH4 TCA.

2004

CH4 TCA, *1019 mol/cm2

4.1 3.9 3.7 3.5 3.3

J

F

M

A

M

J

J

A

S

O

N

D

N

D

Figure 3a. Mean annual cycle of CH4 TCA near St. Petersburg.

4.1

2002

3.9 3.7 3.5 3.3 4.1

2001

3.9 3.7 3.5 3.3 4.1

1995

3.9 3.7 3.5 3.3 4.1

J

F

М

А

М

J

J

А

S

О

1999

3.9 3.7 3.5 3.3 4.1 3.9

J

F

М

А

М

J

J

А

S

О

N

D

2000

3.7 3.5 3.3 Figure 3b. Annual cycles of CH4 TCA for 2002, 2001, 1995, 1999, 2000 years near St. Petersburg.

4. Months with sufficient amount of data were used for CH4 TCA growth rate (GR) estimation for two periods of 19911999 (Table 3, second row) and 1999-2002 (Table 3, third row). GR have been obtained from monthly mean values by linear regression (with weights, which vary as number of measurement days within the months). Table 3. Estimates of CH4 TCA growth rates. Month

CH4 TCA growth rates, %/yr. 1991-1999 1999-2002

February March April May June July August September

1.0±0.8 0.4±0.9 0.02±0.9 -0.1±0.8 0.03±0.7 0.5±1.0 0.3±0.8 0.1±0.9

0.3±0.6 -0.2±0.6 -0.3±0.7 -0.6±0.6 -0.2±0.5 -0.2±0.6 -0.4±0.5 -0.5±0.6

GRs differ for 1991-1999 and 1999-2002 periods and vary from month to month. Last three years GRs of CH4 TCA decrease for almost all months and retain positive only for February. Period of 1999-2002 is characterized by significant decline of CH4 TCA for St. Petersburg region. The suggested reason was already mentioned above (dry summers of 1998-2002).

3. CARBON MONOXIDE TCA TIME SERIES ANALYSIS

CO TCA, *1019 mol/cm2

1. Average annual cycle of CO TCA for the period of 1995-2002 (near St. Petersburg) is given in Fig. 4. CO TCA seasonal variations have mean amplitude of about 25% with maximum in February and minimum during July-August. . Error bars in Fig. 4 are the measure of CO TCA interannual variability. CO interannual variability is greater in autumnwinter due to intensive use of fossil fuel and small number of measurement days.

0.32 0.28 0.24 0.20 0.16 J

F

М

А

М

J

J

А

S

О

N

D

Figure 4. Mean annual cycle of CO TCA near St. Petersburg.

2. GRs were estimated using residuals from monthly means of CO TCA after the average annual cycle have been subtracted. GRs with the error are given in Fig. 5 for two periods: 1995 - September 1998, April 1999 – 2002. October 1998 - March 1999 was excluded from consideration because of strong irregular disturbances of CO were observed for this period. GRs of CO TCA have changed from (3.5±2.3)%/yr for the first period up to (-2.1±1.5)%/yr for the second one.

0.06 (3.5±2.3) %/yr

CO TCA residuals, *1019 mol/cm2

0.03 0 -0.03 -0.06 1995 0.06 0.03

1996

1997

1998

1999

2001

2002

2003

(-2.1±1.5) %/yr

0 -0.03 -0.06 1999

2000

Figure 5. Estimates of CO TCA growth rates near.

4. CARBON MONOXIDE AND METHANE TCA AND AIR MASS ORIGIN NEAR ST. PETERSBURG Air mass trajectory analysis for the days with spectroscopic measurements during 1998-1999 was used to identify source regions and to associate them with various levels of CH4 and CO pollution encountered for the St. Petersburg region. Period of 1998-1999 with irregular disturbances of CO and CH4 TCA was chosen. For trajectory analysis, we employed HYSPLIT-4 isentropic trajectory model of NOAA Air Resources Laboratory [4]. The HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) model is the newest version of a complete system for computing simple air parcel trajectories to complex dispersion and deposition simulations [4]. The territory illustrated in Fig. 6 was divided into five sectors: 1. Arctic Ocean and North Russia; 2. continental Russia and Eurasia; 3. Europe; 4. Baltic Sea; 5. Arctic Ocean and Scandinavia. Five-day backward trajectories were calculated for three elevations above measurement site (50, 1500 and 3000 m above ground level) for each day of spectroscopic observations. Analysis of CH4 and CO TCAs together with backward trajectories at different elevations shows: 1. results for all elevations (50, 1500 and 3000 m above ground level) are similar in general; 2. just trajectories at 1500 m are good indicators of large-scale flow. Therefore, results of air mass origin influence on CH4 and CO TCAs are considered for the 1500 m hereinafter. Percentages in Fig. 6 are the frequency of air masses arriving at St. Petersburg from the chosen sectors. Air masses coming from fifth sector are dominant for the St. Petersburg region. Fig. 7 illustrates distribution of mean, minima and maxima values of CH4 TCA over five sectors. Behavior of mean, minima and maxima values is similar in general. Air mass appears to be highly polluted by CH4 when air originates from the Russian territory (sectors 1 and 2), moderately polluted from Europe, and rather clean from the Baltic Sea, Arctic Ocean and Scandinavia (sectors 4 and 5).

Figure 6. Five most important air mass flow sectors for St. Petersburg.

0.5

CO TCA, *1019 mol/cm2

CH4 TCA, *1019 mol/cm2

4

3.8

3.6

3.4

3.2

0.4

0.3

0.2

0.1

1

2

3

sector

4

5

Figure 7. CH4 TCA distribution over five air mass flow sectors.

1

2

3

sector

4

5

Figure 8. CO TCA distribution over five air mass flow sectors.

Pollution levels of CO for the same sectors are shown in Fig. 8. Enhanced CO levels are observed for air masses originated from the sectors 1 and 2. Clean air is coming from the Baltic Sea, Arctic Ocean and Scandinavia. Distribution of CO pollution levels over sectors repeats qualitatively situation for CH4. Minimal TCAs of CH4 and CO (shown in Fig. 7 and 8) can be regarded as background values of CH4 and CO for corresponding sector. Clear sectors for both gases are the same as for mean values (sectors 5 and 4). Enhanced background values of CH4 are observed for the North Russia and Europe. Minima of CO TCA follow the mean values (see Fig. 8). This study gives an overview of the regional CH4 and CO pollution in the Northwest Russia. It confirms the continental origin of the air masses with enhanced levels of CH4 and CO. Measurement site for spectroscopic observations is situated in 35 km south-westward the St. Petersburg. Important aspect of the study is the megacity (St. Petersburg) influence on obtained results. We have compared our results with the same trajectory analysis having been carried out by colleagues from the Voeikov Main Geophysical Observatory (MGO) for the CH4 mixing ratio measurements. MGO measurement site performs measurements of CH4 mixing ratio in 30 km north-eastward the St. Petersburg [5]. Study of CH4 mixing ratios together with air masses origin has shown results (report of INTAS-RFBR 95-0696 grant) similar to overviewed here. Therefore, we suggest that enhanced level of the gases TCAs for Russia is a result of superposition of continental sources and St. Petersburg pollution. St. Petersburg CH4 emission has not significantly changed distribution of enhanced and clear territories.

5. CONCLUSIONS 1. Period of 1999-2002 is characterized by significant decline of CH4 TCA for the St. Petersburg region. The suggested reason is hot and dry summers of 1999-2002. 2. October 1998 - March 1999 is characterized by the strong irregular disturbances of CO TCA. Growth rates of CO TCA have changed at this period from (3.5±2.3)%/yr (for 1995-1998) up to (-2.1±1.5)%/yr (for 1999-2002). 3. Enhanced CO and CH4 TCA levels are observed for air masses originated from the sectors of the North Russia, continental Russia and the Eurasia. Europe can be classified as moderately polluted territory. Clean air comes from the Baltic Sea, Arctic Ocean and the Scandinavia. Distribution of CO pollution levels over sectors repeats qualitatively situation for CH4.

ACKNOWLEDGEMENTS Study was founded by the Russian Foundation for Basic Research (grants 02-05-64711), St. Petersburg Committee of Science and High School (grant for young Ph.D. scientists PD04-1.5-109). We are also indebted to NOAA Air Resources Laboratory for access the HYSPLIT transport and dispersion model.

REFERENCES 1. Mironenkov A.V., Poberovski A.V., Timofeyev Yu.M., “Spectroscopic observations of methane total column amounts near St. Petersburg”, Izvestiya, Atmospheric and Oceanic physics, V.32, N4, pp.471-478, 1996. 2. Mironenkov A.V., Poberovski A.V., Timofeyev Yu.M., “Gases total column retrieval method”, Izvestiya, Atmospheric and Oceanic physics, V.32, N2, pp.207-215, 1996. 3. Crutzen P.J. ”Variability in atmospheric-chemical systems”, Scales and Global Changes: Spatial and Temporal Variability in Biospheric and Geospheric Processes, edited by T. Rosswall, R.G. Woodmansee and P.G. Risser, pp.81-108, published by John Wiley & Sons Ltd., 1988. 4. http://www.arl.noaa.gov 5. Paramonova N.N., Privalov V.I., Reshetnikov A.I., “Carbon dioxide and methane monitoring in Russia”, Izvestiya, Atmospheric and Oceanic physics, V.37, N1, pp.38-44, 2001.