Elsevier

Atmospheric Environment

Volume 45, Issue 26, August 2011, Pages 4470-4480
Atmospheric Environment

Concentrations of fine, ultrafine, and black carbon particles in auto-rickshaws in New Delhi, India

https://doi.org/10.1016/j.atmosenv.2011.05.028Get rights and content

Abstract

Concentrations of air pollutants from vehicles are elevated along roadways, indicating that human exposure in transportation microenvironments may not be adequately characterized by centrally located monitors. We report results from ∼180 h of real-time measurements of fine particle and black carbon mass concentration (PM2.5, BC) and ultrafine particle number concentration (PN) inside a common vehicle, the auto-rickshaw, in New Delhi, India. Measured exposure concentrations are much higher in this study (geometric mean for ∼60 trip-averaged concentrations: 190 μg m−3 PM2.5, 42 μg m−3 BC, 280 × 103 particles cm−3; GSD ∼1.3 for all three pollutants) than reported for transportation microenvironments in other megacities. In-vehicle concentrations exceeded simultaneously measured ambient levels by 1.5× for PM2.5, 3.6× for BC, and 8.4× for PN. Short-duration peak concentrations (averaging time: 10 s), attributable to exhaust plumes of nearby vehicles, were greater than 300 μg m−3 for PM2.5, 85 μg m−3 for BC, and 650 × 103 particles cm−3 for PN. The incremental increase of within-vehicle concentration above ambient levels—which we attribute to in- and near-roadway emission sources—accounted for 30%, 68% and 86% of time-averaged in-vehicle PM2.5, BC and PN concentrations, respectively. Based on these results, we estimate that one’s exposure during a daily commute by auto-rickshaw in Delhi is as least as large as full-day exposures experienced by urban residents of many high-income countries. This study illuminates an environmental health concern that may be common in many populous, low-income cities.

Graphical abstract

Highlights

► We collected ∼180 h of particle exposure measurements in New Delhi auto-rickshaws. ► In-vehicle particle concentrations high relative to New Delhi background levels. ► Roadway emissions are dominant source of in-vehicle UFP and BC exposure. ► Concentrations among highest reported for a megacity transportation setting.

Introduction

New Delhi, India, is among the ten largest metropolitan areas worldwide, with an estimated year-2003 population of 18.6 million people (Forstall et al., 2009). Particulate air pollution has been a longstanding problem in Delhi. Ambient concentrations of PM2.5 and PM10 (mass concentrations of airborne particles with aerodynamic diameters, dp, less than 2.5 and 10 μm, respectively) are regularly among the highest in the world and frequently an order of magnitude larger than in US cities (Gurjar et al., 2008, Mage et al., 1996). Air quality management efforts in Delhi devote special attention to vehicle emissions. Many private and public transit vehicles have been converted to operate using compressed natural gas (CNG) fuel, and two-stroke vehicles are being phased out of use (Reynolds and Kandlikar, 2008). However, owing to rapid increases in private motor vehicle use, the Delhi transportation sector remains a large and growing source of air pollution in that metropolis (Narain et al., 2010).

Research from around the world indicates that particle concentrations in transportation microenvironments – on and near roadways and inside vehicles – often exceed nearby ambient levels. Therefore exposures of people while in transit and for those who live or work near roadways may not be well characterized by conventional air quality monitoring stations (Kaur et al., 2007). Short-term exposure to elevated in-vehicle particle concentrations has been associated with subclinical cardiovascular effects in healthy populations (Riediker et al., 2004, Jacobs et al., 2010), and might serve as a trigger of acute health effects (e.g., myocardial infarction) for susceptible individuals (Peters et al., 2004). Relatively few studies have investigated in-traffic exposures to particulate air pollution in developing-world megacities (Han and Naeher, 2006). Such exposures are of concern owing to high-emitting vehicle fleets, rapid increases in vehicle use, and long exposure durations in and near traffic. For example, a 1997 study in Delhi reported that concentrations of PM5.0 and CO inside vehicles exceeded the high urban background concentrations by 1.5–10×, depending on vehicle type (Saksena et al., 2007).

In view of the limited data on this important air quality issue, we undertook an investigation of the ambient and in-vehicle concentrations in New Delhi of three constituents of vehicle exhaust: fine particles (PM2.5), black carbon (BC), and ultrafine particle number (PN). Epidemiological evidence links PM2.5 exposure to elevated risks for several acute and chronic health outcomes, including cardiovascular disease and premature mortality (Pope and Dockery, 2006, Brook et al., 2010). Black carbon – a product of incomplete combustion and a component of PM2.5 – is associated with “probable” human carcinogens such as diesel exhaust (IARC, 1989) and polycyclic aromatic hydrocarbons (IARC, 1983). Particle number is typically dominated by ultrafine particles (UFP; diameter < 0.1 μm), which are abundant in vehicle exhaust (Kittelson, 1998) and are an emerging public health concern (Oberdörster, 2001, Delfino et al., 2005). To our knowledge, the research reported here constitutes the first published study that characterizes in-vehicle exposure concentrations to BC and PN on the Indian subcontinent. In addition, the measurements presented here represent one of the largest datasets for real-time, in-vehicle particle concentrations sampled anywhere.

Section snippets

Site description and experimental design

New Delhi is India’s capital and one of the country’s more affluent cities. The region experiences cool winters (Dec–Jan); a brief, transitional spring (Feb–Mar); hot, dry summers (Apr–Jun); a hot, humid monsoon season (Jul–Sep); and a warm, dry post-monsoon season (Oct–Nov). Our study, conducted from February through May, spans the early spring through mid-summer period in Delhi. In this study, in-vehicle concentration measurements were collected primarily inside auto-rickshaws, a

In-vehicle concentrations: auto-rickshaws

Particle concentrations measured in auto-rickshaws were high. Trip-averaged concentrations were approximately lognormally distributed (Fig. 3), with geometric means of 190 μg m−3 for PM2.5, 42 μg m−3 for BC, and 280 × 103 particles cm−3 for PN (Table 2). Concentrations were elevated in-vehicle relative to ambient measurements at CRP, which had geometric means of 130 μg m−3 for PM2.5, 12 μg m−3 for BC, and 35 × 103 particles cm−3 for PN. Over all trips, the arithmetic mean incremental in-vehicle

Conclusions

We measured in-vehicle exposure concentrations to particulate air pollution for auto-rickshaw and car commuters during three months in New Delhi, India. This paper reports one of the first sets of PN and BC exposure concentration measurements inside auto-rickshaws, a ubiquitous transport mode in South Asian urban areas. It also represents one of the longest-duration measurement campaigns of real-time, in-vehicle PN and BC concentrations anywhere. Auto-rickshaw exposure concentrations of PM2.5,

Acknowledgments

The authors thank A. Sagar and G. Tiwari for hosting one of us (JSA) at the Indian Institute of Technology, Delhi during field research. We thank M. Apte, J. Blair, M. Brauer, A. Grieshop, L. Gundel, S. Guttikunda, O. Hadley, T. Hansen, M. Lunden, C. Reynolds, and K. Smith for technical assistance and feedback. In addition, we gratefully acknowledge the efforts of our research assistant Phoolchand. Efforts by JSA were partially supported by a Fulbright-Nehru grant from the US-India Educational

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