The Los Angeles basin has frequent occurrences of ozone concentrations which exceed the National Ambient Air Quality Standard. High levels of ozone can be damaging to human cardiovascular and respiratory health. The chemical reactions that produce ozone involve a mix of sunlight and either nitrogen oxides (NOx) or volatile organic carbon molecules (VOC). These precursors, NOx and VOC, are strongly associated with ozone production but it is not a one-to-one relationship. Researchers from University of California Berkeley recently published a study looking at the role of NOx and VOC in ozone reduction.The researchers, funded in part by CPO’s Atmospheric Chemistry, Carbon Cycle, & Climate (AC4) program, were interested in if additional emission reductions, which typically target vehicle emissions, would usefully impact the high ozone events in the Los Angeles basin. Variations in day-to-day emissions of ozone precursors are dependent on temperature, as many VOC reactions seem to be heavily heat-dependent, and weekday-limited vehicle type, as heavy-duty trucking and associated emissions of NOx occurs more on workdays than the weekends. With two decades of observations, this Environmental Science & Technology study provides a benchmark for investigating the co-occurence of heat waves and high ozone. Further, any reductions in ozone will have to target both temperature concerns (hard to do in a changing climate) and further reductions in NOx emissions. Notably, vehicle emissions of VOC have decreased so much in the past two decades that other sources (e.g., volatile consumer products) are larger contributors to the total Los Angeles VOC.
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