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Proc Natl Acad Sci U S A. 2017 Jul 3;114(27):6984-6989. doi: 10.1073/pnas.1620911114. Epub 2017 Jun 19.

Reducing secondary organic aerosol formation from gasoline vehicle exhaust.

Author information

1
Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA 15213.
2
Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213.
3
Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720.
4
Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213.
5
Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA 15213; alr@andrew.cmu.edu.

Abstract

On-road gasoline vehicles are a major source of secondary organic aerosol (SOA) in urban areas. We investigated SOA formation by oxidizing dilute, ambient-level exhaust concentrations from a fleet of on-road gasoline vehicles in a smog chamber. We measured less SOA formation from newer vehicles meeting more stringent emissions standards. This suggests that the natural replacement of older vehicles with newer ones that meet more stringent emissions standards should reduce SOA levels in urban environments. However, SOA production depends on both precursor concentrations (emissions) and atmospheric chemistry (SOA yields). We found a strongly nonlinear relationship between SOA formation and the ratio of nonmethane organic gas to oxides of nitrogen (NOx) (NMOG:NOx), which affects the fate of peroxy radicals. For example, changing the NMOG:NOx from 4 to 10 ppbC/ppbNOx increased the SOA yield from dilute gasoline vehicle exhaust by a factor of 8. We investigated the implications of this relationship for the Los Angeles area. Although organic gas emissions from gasoline vehicles in Los Angeles are expected to fall by almost 80% over the next two decades, we predict no reduction in SOA production from these emissions due to the effects of rising NMOG:NOx on SOA yields. This highlights the importance of integrated emission control policies for NOx and organic gases.

KEYWORDS:

NOx; air pollution; atmospheric particulate matter; gasoline vehicles; secondary organic aerosol

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