Concentrations of Particulate Matter in New Delhi Vehicles

(with Bill Nazaroff, Julian Marshall, and Thomas Kirchstetter)

Time spent in and near vehicles represents a potentially important source of daily air pollution exposure that is not well-characterized by traditional ambient air pollution monitoring systems. Relatively few studies have investigated in-vehicle exposure to particulate matter in low-income cities. To help fill this data gap, we undertook a field measurement campaign to characterize pollution concentrations inside New Delhi vehicles. Our study was motivated by several factors that we thought might lead to especially high exposures for Delhi commuters, such as congested traffic and relatively high-emitting vehicles.

We measured concentrations of fine particles
(PM2.5), black carbon (BC) and ultrafine particles (UFP) breathed by occupants of auto-rickshaws and conventional cars a fixed 40 km route in New Delhi. During 75 rush-hour trips from Feb - May 2010, we collected roughly 200 hours of in-vehicle concentration measurements at 1 second time resolution. Dashboard video footage and onboard GPS were used to fix the measurements in space and time. Simultaneously, we monitored urban background particle concentrations at a fixed site in a upper-income residential neighborhood.

Overall, in-vehicle levels of particulate matter were very high. Short-term peak concentrations of all pollutants were dozens of times greater than urban background levels. The above video shows one example: an encounter with a super-emitting truck, where PM2.5 exposure concentrations briefly exceeded 2,000 µg m-3. Time-average in-vehicle concentrations of all pollutants substantially exceeded ambient levels. In-vehicle PM2.5 levels were ~40% higher than urban background levels, while BC mass and UFP number concentrations were respectively ~4x and ~8× higher than ambient. Mean concentrations in auto-rickshaws (200 µg m-3 PM2.5, 43 µg m-3 BC and 290,000 particles cm-3) are among the highest values ever reported for a routine transportation microenvironment. (For context, typical annual-average ambient PM2.5 concentrations in US cities are on the order of 10 - 20 µg m-3).

Journal article: Apte JS, Kirchstetter TW, Reich AH, Deshpande SJ, Kaushik G, Chel A, Marshall JD, Nazaroff WW. 2011. Concentrations of fine, ultrafine, and black carbon particles in auto-rickshaws in New Delhi, India. Atmospheric Environment 45, 4470-4480. [link]

News coverage: [Associated Press] [Times of India] [Deutsche Welle]
2011: [Indian Express] [Environmental Research Web]