wxman
Veteran Member
As has been discussed on this board many times, it has been known for decades that large reductions in NOx emissions in certain locations can lead to an increase in ambient ozone levels ("weekend effect"). This mostly occurs in large metropolitan areas.
A paper just published in the Proceedings of the National Academy of Sciences shows that reductions in ambient NOx levels can lead to increases in formation of secondary particulate matter (secondary organic aerosols - SOA).
Abstract:
Thus regulators need to evaluate their approach to NOx and VOC emission controls carefully.
A paper just published in the Proceedings of the National Academy of Sciences shows that reductions in ambient NOx levels can lead to increases in formation of secondary particulate matter (secondary organic aerosols - SOA).
Abstract:
http://www.pnas.org/content/early/2017/06/13/1620911114.abstractOn-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.
Thus regulators need to evaluate their approach to NOx and VOC emission controls carefully.