Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA 15213.
Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213.
Proc Natl Acad Sci U S A. 2017 Jul 3;114(27):6984-6989. doi: 10.1073/pnas.1620911114. Epub 2017 Jun 19.
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 (NO) (NMOG:NO), which affects the fate of peroxy radicals. For example, changing the NMOG:NO from 4 to 10 ppbC/ppbNO 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:NO on SOA yields. This highlights the importance of integrated emission control policies for NO and organic gases.
道路上的汽油车是城市中二次有机气溶胶 (SOA) 的主要来源。我们在烟雾室中氧化了来自道路上的汽油车车队的稀释的、环境水平的废气浓度，研究了 SOA 的形成。我们发现，满足更严格排放标准的较新型车辆产生的 SOA 形成量较少。这表明，用符合更严格排放标准的较新型车辆自然取代较旧车辆应降低城市环境中的 SOA 水平。然而，SOA 的产生既取决于前体浓度（排放），又取决于大气化学（SOA 产率）。我们发现 SOA 形成与非甲烷有机气体与氮氧化物（NO）的比例（NMOG:NO）之间存在强烈的非线性关系，这影响了过氧自由基的命运。例如，将 NMOG:NO 从 4 变为 10 ppbC/ppbNO，会使从稀汽油车废气中产生的 SOA 产率增加 8 倍。我们研究了这种关系对洛杉矶地区的影响。尽管未来 20 年内洛杉矶汽油车的有机气体排放量预计将下降近 80%，但由于 NMOG:NO 对 SOA 产率的影响，我们预计这些排放物的 SOA 产生不会减少。这凸显了综合排放控制政策对 NO 和有机气体的重要性。
