Post Date: 7 September 2018

Linking Tailpipe to Atmosphere: Reducing Secondary Organic Aerosol Formation from Gasoline Vehicle Exhaust

Abstract

On-road gasoline vehicles are a major source of secondary organic aerosol (SOA) in urban areas. To better understand SOA formation from gasoline vehicles, a study was carried out to investigate SOA formation by oxidizing dilute, ambient-level exhaust concentrations from a fleet of on-road gasoline vehicles in a smog chamber. Less SOA formation from newer vehicles meeting more stringent emissions standards was observed. 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). A strongly nonlinear relationship between SOA formation and the ratio of non-methane-organic-gas-to-NOx (NMOG:NOx) is found. 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. The implications of this relationship were investigated 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 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.

Bio 

Dr. Yunliang Zhao is an Air Pollution Specialist and the lead staff of the technique team for the community air monitoring near petroleum sources at California Air Resources Board (CARB). Dr. Zhao received his Ph.D. from the University of California, Berkeley; then, moved to Carnegie Mellon University working as a postdoctoral fellow and a research scientist prior to joining CARB. Dr. Zhao’s research primarily focuses on investigating emissions of organics from primary sources and their chemical transformation in the atmosphere by integrating the instrument development, source test, smog chamber simulation, ambient measurements and modeling. He developed a novel thermal desorption gas chromatography-mass spectrometry instrument and data analysis approach for quantification of previously unquantified compounds to enable the mass closure analysis of organics in source emissions. He found a nonlinear relationship between NOx levels and secondary organic aerosol from gasoline vehicles. His finding highlights the importance of integrated emission control policies for both NOx and organic gases. Dr. Zhao is active in research and publishing. His research has been published in PNAS, Nature Geo, ES&T, etc. To date, he has produced 27 peer-reviewed publications and is the first author on 12 of them.