Understanding the Paths of Surface Ozone Abatement in the Los Angeles Basin

Abstract

Ozone in the urban atmosphere can accumulate from photochemistry involving nitrogen oxides, carbon monoxide, and volatile organic compounds mainly emitted from fossil fuel combustions and volatile chemical products. Concentrated ozone near the earth's surface has a detrimental impact on the ecosystem and our health. The Los Angeles Basin is a classic example of an urban region with long‐standing ozone pollution, frequently in violation of its standard, designated by the US Environmental Protection Agency (EPA). Studies have reported substantial declines of ozone and their precursor concentrations over the past half century in this area due to extensive pollution controls. Since 2000, however, the ozone design value has remained the same and has not been able to fully reach the air quality standard set by the EPA despite decreases in its precursor concentrations. To understand this phenomenon, we utilize a chemical transport modeling approach to reproduce historical ozone trends and to conduct sensitivity runs relative to a 2010 baseline. Based on our analysis of the model simulations comparing the weekends and weekdays, rather than focusing only on the weekly averages, we diagnose that the Los Angeles Basin is actually going under a significant transition in photochemistry toward a lower ozone concentration. This reveals how air quality management strategies are slowly moving towards a pathway of reducing ozone concentrations in the future. Our study, however, suggests that further reductions of NOx emissions can lead to continued improvement of ozone pollution in this area.

Elucidating Contributions of Anthropogenic Volatile Organic Compounds and Particulate Matter to Ozone Trends over China

“…Finally, the analysis over CY uniquely indicates steady increase of VOC, consistent with Simayi et al 70 that implies recent increases of industrial VOC emissions over this region (as a new nationlevel economic center since 2010s) were among the strongest across China. Notably, these unprecedentedly detailed insights build a broad connection of current O 3 mitigation over China to historical success experienced over the United States during the last three decades, 26,49,51 both indicating strong dependence on effective VOC controls. Our analysis of de-weathered observations also clarifies the effects of PM 2.5 .…”

“…Of note, changes in anthropogenic VOC have been relatively less discussed than NO x or aerosol in these previous studies of Chinese urban O 3 . However, VOCs are well known to be important and have been identified as contributors to O 3 trends elsewhere. ,,− Although China has initialized regular VOC monitoring plan since 2019, publicly accessible data set is not yet available. Although anthropogenic VOC emissions in China were estimated to change less than NO x since 2013, , there is a lack of observational evidence one way or the other on the role of VOC control in the interpretation of O 3 trends in China.…”

Direct observations of NOx emissions over the San Joaquin Valley using airborne flux measurements during RECAP-CA 2021 field campaign

“…with the same model configuration described in Kim et al (2022). The Berkeley Dalhousie Iowa Soil NO Parameterization (BDISNP) (Hudman et al, 2012;Sha et al, 2021) is also used in a number of models.…”

Comparison between Spatially Resolved Airborne Flux Measurements and Emission Inventories of Volatile Organic Compounds in Los Angeles

“…Since then, ozone and PM 2.5 particle pollution have ceased declining. 5,6 Recent studies suggest that vehicular VOC emissions (while still decreasing) are no longer dominant, and that other VOC sources, such as volatile chemical products (VCPs), are less well understood but becoming more important. 7−9 Emission inventories are the basis for atmospheric chemistry models used to predict air quality and inform policymaking.…”

“…Emission regulations introduced since the 1970s reduced vehicular VOC emissions, along with ozone and PM 2.5 in Los Angeles until ∼2010. Since then, ozone and PM 2.5 particle pollution have ceased declining. , Recent studies suggest that vehicular VOC emissions (while still decreasing) are no longer dominant, and that other VOC sources, such as volatile chemical products (VCPs), are less well understood but becoming more important. − …”