Commuter exposure to black carbon particles on

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Environ Sci Pollut Res https://doi.org/10.1007/s11356-017-0517-x

RESEARCH ARTICLE

Commuter exposure to black carbon particles on diesel buses, on bicycles and on foot: a case study in a Brazilian city Admir Créso Targino 1 & Marcos Vinicius C. Rodrigues 2 & Patricia Krecl 1 & Yago Alonso Cipoli 2 & João Paulo M. Ribeiro 2

Received: 26 July 2017 / Accepted: 18 October 2017 # Springer-Verlag GmbH Germany 2017

Abstract Commuting in urban environments accounts for a large fraction of the daily dose of inhaled air pollutants, especially in countries where vehicles have old technologies or run on dirty fuels. We measured black carbon (BC) concentrations during bus, walk and bicycle commutes in a Brazilian city and found a large spatial variability across the surveyed area, with median values between 2.5 and 12.0 μg m−3. Traffic volume on roadways (especially the number of heavy-duty diesel vehicles), self-pollution from the bus tailpipe, number of stops along the route and displacement speed were the main drivers of air pollution on the buses. BC concentrations increased abruptly at or close to traffic signals and bus stops, causing in-cabin peaks as large as 60.0 μg m−3. BC hotspots for the walk mode coincided with the locations of bus stops and traffic signals, whilst measurements along a cycle lane located 12 m from the kerb were less affected. The median BC concentrations of the two active modes were significantly lower than the concentrations inside the bus, with a bus/walk and bus/bicycle ratios of up to 6. However, the greater inhalation rates of cyclist and pedestrians yielded larger doses (2.6 and 3.5 μg on a 1.5-km commute), suggesting that the greater physical effort during the active commute may outweigh the reduction in exposure due to the shift from passive to active transport modes.

Responsible editor: Philippe Garrigues * Admir Créso Targino [email protected]

1

Graduate Program in Environmental Engineering, Federal University of Technology, Av. Pioneiros 3131, Londrina 86036-370, Brazil

2

Department of Environmental Engineering, Federal University of Technology, Av. Pioneiros 3131, Londrina 86036-370, Brazil

Keywords Mobile measurements . Urban air pollution . Transportation modes . Human health . Population exposure . Environmental justice

Introduction The choice of commuting mode varies greatly in cities and depends on local factors, such as transport policies, weather, socioeconomic status, neighbourhoods’ infrastructure and individual preferences. Buehler (2011) showed that policies that integrate public transportation timetables and tickets making car use more expensive and slower may explain the choice of more sustainable transport in Germany compared to the USA. Böcker et al. (2016) and Creemers et al. (2015) showed that warm outdoor temperatures enhance walking and cycling over the use of motorised transport modes in the Netherlands, whereas rainy and windy conditions have opposite effects. Cultural aspects may also affect this choice, and in many business segments, commuting by other means of transport than a private car would indicate a loss of face before coworkers (e.g. Zhou and Hui 2003). Time budget surveys conducted in many countries have revealed that the percentage of time urban dwellers spend in transport microenvironments accounts for a small fraction of their daily activities. An employed person in the USA, France and Belgium spends only 6% of the day in motorised transport, whilst in Florence (Italy) and Londrina (Brazil), the values are 9.7 and 7.0%, respectively (Carvalho 2017; Dons et al. 2012; Fondelli et al. 2008; Klepeis et al. 2001). Vasconcellos (2013) reported that the commuting time by bus in Caracas, Mexico City and São Paulo may be double that of a trip by car. In this way, people who attempt to replace car trips by bus in these cities face discomfort and longer commutes. Although most commuters spend a small fraction

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of the day on or in the proximity of motorised vehicles, the high pollution levels within transport environments may account for between 20 and 36% of the daily exposure to black carbon (BC) particles, depending on the transportation mode (Williams and Knibbs 2016; Dons et al. 2012). BC is a specific marker of combustion processes and ubiquitous in urban environments dominated by motorised traffic. Over the last couple of years, a body of urban air quality research has shown that the personal exposure to different particulate metrics in urban transport microenvironments is highly variable and influenced by the commuting mode. A comprehensible review by Cepeda et al. (2017) including active (pedestrian and cyclist) and motorised commutes across North America, west Pacific and Southeast Asia concluded that car and bus commuters had the highest levels of air pollution exposure, followed by those commuting by a car with controlled ventilation settings, cyclists and pedestrians, whereas the lowest levels were experienced by massive motorised transport. On the other hand, Rivas et al. (2017), Betancourt et al. (2017), Suárez et al. (2014) and Fondelli et al. (2008) found that the exposure concentration to particulates was significantly lower for commuters in cars than for commuters on buses in London, Bogotá, Santiago de Chile and Florence, respectively. Nazelle et al. (2016) also found inconsistencies when reviewing air pollution exposure for various modes of transport in European cities and suggested that differences in the fleet characteristics (in particular fuel, technology and ventilation settings on public transport) may account for part of the discrepancies across studies. Comparatively, much less information is available on personal exposure across different transit modes in emerging economies. More specifically, Latin American cities are under-represented, with only a few studies in Bogotá, Santiago de Chile and Mexico City (Betancourt et al. 2017; Suárez et al. 2014; Gómez-Perales et al. 2004). Nevertheless, the few Latin American studies revealed that the air pollutant concentrations are disproportionately larger on buses. For example, Suárez et al. (2014) measured particle concentrations on 137 active and passive commutes in Santiago de Chile in different seasons of the year and on a variety of sampling conditions. They showed that the mean PM 2.5 concentration was 17.5 μg m−3 on buses and 2.0 μg m−3 in cars, suggesting that the exposure in different modes of transport may not only be heterogeneous but also inequitable. These regional results highlight that during their daily commutes, the population without access to private transportation may fall in a case of environmental injustice, defined as Binequitable and disproportionately heavy exposure of poor, minority, and disenfranchised populations to toxic chemicals, contaminated air and water, unsafe workplaces, and other environmental hazards^ (Bullard and Wright 1993). With a tendency of operating old and poorly maintained urban bus fleets—for example, an average age

of 12 years in Montevideo and 20 years in Lima (CAF Observatorio de Movilidad Urbana para América Latina 2009)—the benefits of mass public transportation in Latin America may be offset by the increased risks of exposure to high levels of air pollutants. Lamarque et al. (2010) showed that the transportation sector is the largest source of anthropogenic BC emissions in Latin America and diesel engines are the largest contributors within this sector. Other relevant sources include emissions from agricultural and domestic burning (Bond et al. 2013; Targino and Krecl 2016). Targino et al. (2016) and Krecl et al. (2016) found strong relationships between BC concentrations and the number of heavy-duty diesel-fuelled vehicles (HDDV) in a Brazilian city. These relationships have severe negative implications on human health, as epidemiological studies showed robust associations between traffic density and early all-cause mortality and/or cardiovascular or cardiopulmonary diseases (e.g. Grahame et al. 2014). Janssen et al. (2011) showed that reducing a unit of BC mass concentrations will lengthen life four to nine times more than reducing a comparable amount of PM2.5 mass, and Hoek et al. (2013) reported that premature mortality associated with long-term exposure to elemental carbon would be reduced by 6% per 1.0 μg m−3. The present study aims to contribute to fill a research gap in the area of personal exposure to air pollution in Brazil. We present BC concentrations measured on urban public bus routes and discuss the causes of their spatial variability. We highlight the importance of conducting exposure studies in medium-sized cities (100,000–600,000 inhabitants) since they are abundant and host about 30% of Brazil’s 205 million inhabitants. Hence, our findings could be extended to a large fraction of cities in the country with similar vehicle fleet share, fuel composition, urban design and choice of commuting mode. An added value to this study is the assessment of BC concentrations and potential inhaled dose along a sidewalk and a bicycle lane running parallel to the bus route.

Methods Study area This study took place in Londrina, a city of approximately 550,000 inhabitants located in the southern Brazilian state of Paraná (lat. 23° 18′ 36″ S, lon. 51° 09′ 46″ W, alt. 630 m above sea level). The city’s vehicle fleet is largely dominated by passenger cars (78%) with the following share according to the fuel use: 52% gasoline-powered units, 33% flexible-fuel engines (that run on gasoline, hydrated ethanol or any blend of these fuels), 5% run on hydrated ethanol and 7% on diesel (Krecl et al. 2016). Targino and Krecl (2016) reported that the fleet grew 85% between 2005 and 2014 and the increase

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was more significant for motorcycles (67.6%) as an affordable alternative to the inefficient public transport system. The only means of public transport consists of a network of 419 dieselfuelled buses as of 2017. The vehicle ownership reached 671 vehicles per 1000 inhabitants in December 2016, which is much higher than the national number (436 vehicles per 1000 inhabitants). In Londrina, all diesel used for on-road transport has a blend of 6% of biodiesel; 28% of the city’s public bus fleet were manufactured from 2012 onwards, have technology equivalent to Euro V and run on S10 diesel (S content of less than 10 mg kg−1); the rest consists of buses equivalent to Euro III running on S500 diesel. Diesel buses in Brazil are not equipped with diesel particle filters (DPF). Hence, without this technology, the particle emission factors of Londrina’s urban buses may be larger than its European counterparts. For example, Fleischman et al. (2017) found that particle filtration efficiency was on average 96% for particles in the size range of 23–560 nm when Euro III buses were retrofitted with DPF.

1.05 and y-intercepts 55

−1

Driving speed [km h ]

Fig. 5 In-cabin median BC concentrations as a function of driving speed

Comparison of exposure during walk, bicycle and bus commutes The median BC concentrations of the two active modes measured simultaneously with the bus sampling are shown in Fig. 7a, b. The values for the active modes were considerably lower (3.0 and 4.1 μg m−3 for bicycling and walking, respectively) than on the bus (10.3 μg m−3). The largest concentrations for the bicycle mode were found within the first 350 m of the transect where the bicycle lane is close to a five-way signalised intersection causing vehicles to idle longer and pollutants to accumulate. Thereafter, the concentrations remained mostly between 2.0 and 4.0 μg m−3. The walk mode showed concentrations larger than 5.0 μg m−3 coinciding with the locations of bus stops and traffic signals. Since the walk mode data were collected on the sidewalk about 2 m from the kerb, the measurements were more affected by the exhaust emissions of buses at stops and vehicles idling at the traffic signals, than the measurements on the bicycle which used a lane about 12 m from the kerb (except in the beginning of the transect, as described above). This is especially important considering that most buses in the study area have exhaust pipes at the rear and below the bus, which means that the exhaust plume was closer to the sampling line and breathing zone during the walk commute. The separation between the bicycle lane and the motor

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Fig. 6 Mean bus speed along the surveyed route

The median BC concentrations inside the bus were mostly larger than 10.0 μg m −3 , with concentrations below 5.0 μg m−3 only a few blocks towards the end of the transect. The ratio between BC concentrations on the bus and the active

vehicle traffic has been reported to be one of the most important factors affecting the exposure of cyclists to particulate matter (Peters et al. 2014; Kendrick et al. 2011), with drops in exposure concentrations with increasing distance. Table 4 Relationships between vehicle rates and median BC concentrations

HDDV rate [vehicles h−1]

BC [μg m−3]

Total vehicle rate [vehicles h−1]

BC [μg m−3]

< 45 45–90 90–135 135–180 >180

5.1 7.1 6.0 17.7 25.1

< 350 350–700 700–1050 1050–1400 1400–1750 > 1750

1.1 9.0 15.6 1.8 4.0 17.0

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ƒFig. 7

a, b Map of median BC concentrations aggregated to 65-m polygons for the three commuting modes. Upper panel: bicycling (squares) and walking (circles); lower panel: by bus. Mind the different scales in the figures, since the concentrations measured on active the modes were substantially lower than on the bus

modes reached up to six on some sections of the road. These findings agree with the study by Betancourt et al. (2017) who observed that the exposure of pedestrians and cyclists to BC was 6.5-fold lower than diesel bus commuters in Bogotá, and Zuurbier et al. (2010) who found that the average PM10 concentration was higher inside the cabin of diesel buses and lower in bicycle paths in both dense and light traffic areas of Arnhem (the Netherlands). Lim et al. (2015) discuss that commuters using motorised transport with open windows (as is the case in Londrina’s buses) increase their exposure to high pollutant concentrations at hotspots, such as intersections and traffic lights. In their review, Cepeda et al. (2017) also reported that bus commuters had higher levels of particulate matter exposure than cyclists and pedestrians. We found that the median BC concentrations of the bus dataset were statistically different from the active modes (p ≃ 10−8), but the medians between walking and cycling were not statistically different (p = 0.06), when applying the non-parametric Kruskal–Wallis test at a significance level of 0.05. Potential inhaled dose whilst commuting Although bus passengers were exposed to significantly larger BC concentrations than cyclists or pedestrian travelling the same street transect, the higher inhalation rates of commuters using active modes may offset this effect. Hence, we calculated the potential inhaled dose using Eq. 1 and the ventilatory parameters of Table 1. We used the average displacement speeds (GPS-based data) of the bicycle, pedestrian and buses along the 1.5-km transect to estimate the time spent within each polygon. With speeds of 9.8, 4.5 and 20.0 km h−1, respectively, the average times ti within each 65-m polygon for these modes were 0.390, 0.867 and 0.195 min, yielding median potential inhaled doses for the bus, bicycle and walk commutes of 0.8, 2.6 and 3.5 μg, respectively. These numbers show clearly how the ventilation rates and time spent along the route affected the potential dose. Although we observed the lowest median BC concentration for the walk mode, the pedestrian spent more time within each polygon and had a higher ventilation rate compared to the bus commuter, which resulted in the largest dose. The cyclist crossed each polygon twice as fast as the pedestrian; however, the almost 5-fold higher inhalation rate yielded the second largest dose. Twelve studies reviewed by Cepeda et al. (2017) also reported similar results for inhalation rates as ours, except that cyclists followed by pedestrians had the highest dose. Nevertheless, our results are in agreement with most studies which attribute

lower inhalation rate whilst sitting on the bus and the faster displacement speed as keys factors to smaller inhaled dose. Although the doses for active modes were considerably higher than for the bus commute, many researchers advocate that the benefits of cycling and walking outweigh the risks posed by air pollution (e.g. Tainio et al. 2016; Cepeda et al. 2017 and references therein). However, another aspect to be considered is that whilst active commuting and sustainable mobility have been promoted as alternatives to alleviate traffic congestions and bring health and environmental benefits, dwellers of cities in developing countries count on precarious or non-existent facilities for walking and cycling, leaving them to share space with motorised traffic. In such cases, the risk of injury may offset many of the gains of physical activity. According to the WHO (2013), 27% of global road traffic deaths are among pedestrians and cyclists.

Conclusions We found a large spatial variability in the median concentrations of BC measured on buses, ranging from 2.5 to 12.0 μg m−3, with the greatest values in areas dominated by high rates of HDDV. The concentrations were on average 7fold higher than ambient concentrations at a suburban background site and about 3-fold higher than fixed BC measurements conducted within the urban canyon section of the bus route. Stops along the route caused abrupt BC peaks in the cabin (larger than 30.0 μg m−3), with frequent stops contributing for the build-up of BC levels. Hence, large in-cabin concentrations were found on congested roads due to a combination of factors, such as increased traffic density surrounding the bus, self-pollution, lower driving speed and stops. The BC peaks along the sidewalk coincided with the locations of bus stops and traffic signals, thereby confirming that pedestrians walking close to the kerb can be more affected by emission bursts from proximate traffic than bicyclist using a dedicated lane about 12 m from the kerb. The median BC concentration of the bus dataset was statistically larger (10.3 μg m−3) than the active modes (3.0 and 4.1 μg m−3 for bicycling and walking, respectively). However, the high inhalation rate whilst bicycling and walking increased more than four times the potential inhalation dose over a fixed distance. We observed that cyclists and pedestrians may inhale BC doses between 2.6 and 3.5 μg on a 1.5-km commute. Pedestrians tend to choose routes based on length, safety and urban layout, so the values of exposure and dose for walking on alternative paths may differ from the ones shown here. On the other hand, the cycle lane we investigated has a typical layout found in Brazilian cities, where cycling routes are usually built alongside roads to take advantage of existing infrastructure. Hence, bicyclists are likely to use lanes in proximity to motorised sources of air pollution and be exposed to

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BC concentrations similar to what we reported. As to the bus results, given that the technology of the bus fleet in Brazil is highly variable (on average, 10 years), the amount of BC particles that enters the cabin due to self-pollution will be variable and will depend on the predominant technology. The impact of other particle sources, such as the intrusion of BC caused by emissions from proximate traffic, will depend on the vehicle density and fleet share. This is a pioneering study in Brazil and the results presented here should be regarded as an eye opener for policymakers and city planners. As of December 2015, there were 267 medium-sized cities in Brazil, accounting for about 30% of the country’s population. Hence, our findings could be extended to a large number of cities with similar driving patterns, vehicle fleet share, fuel composition and patterns of urban built-up areas. The abatement of large BC exposures should follow a holistic approach, such as targeting emissions from HDDV fleets, facilitating steady flow traffic to reduce fumes from stop-go driving, separation of cyclists from motorised traffic and promoting the walk commutes on low-density roads. One limitation of this study is the lack of measured inhalation rates; however, our numbers give estimates of the potential dose during the different commutes. Acknowledgments We thank Thais Caporal Borges for the help with the data collection and the two anonymous reviewers for their valuable suggestions. Funding information This research was supported by grants 404146/ 2013-9 and 400273/2014-4 from the National Council for Scientific and Technological Development of Brazil (CNPq).

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