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

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 (PM_2.5, 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 PM_2.5, 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 PM_2.5, 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 PM_2.5, 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 PM_2.5, 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.