Two Decades of Changes in Summertime Ozone Production in California’s South Coast Air Basin

• Published in: Environmental science & technology Vol. 56; no. 15; pp. 10586 - 10595
• Main Authors: Perdigones, Begie C., Lee, Soojin, Cohen, Ronald C., Park, Jeong-Hoo, Min, Kyung-Eun
• Format: Journal Article
• Language: English
• Published: Easton American Chemical Society 02.08.2022
• Subjects: Agricultural production; Air pollution; Air quality; Air quality standards; Anthropogenic Impacts on the Atmosphere; Basins; Emissions; Health risks; Nitrogen oxides; Organic compounds; Outdoor air quality; Ozone; Photochemicals; Pollutants; Summer; Tracking control; VOCs; Volatile organic compounds; Weather; United States > US; California; prediction; tropospheric ozone; ozone production sensitivity; regulation; ozone production rate; air quality
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.2c01026

Tropospheric ozone (O3) continues to be a threat to human health and agricultural productivity. While O3 control is challenging, tracking underlying formation mechanisms provides insights for regulatory directions. Here, we describe a comprehensive analysis of the effects of changing emissions on O3 formation mechanisms with observational evidence. We present a new approach that provides a quantitative metric for the ozone production rate (OPR) and its sensitivity to precursor levels by interpreting two decades of in situ observations of the six criteria air pollutants(2001–2018). Applying to the South Coast Air Basin (SoCAB), California, we show that by 2016–2018, the basin was at the transition region between nitrogen oxide (NO x )-limited and volatile organic compound (VOC)-limited chemical regimes. Assuming future weather conditions are similar to 2016–2018, we predict that NO x -focused reduction is required to reduce the number of summer days the SoCAB is in violation of the National Ambient Air Quality Standard (70 ppbv) for O3. Roughly, ∼40% (∼60%) NO x reductions are required to reduce the OPR by ∼1.8 ppb/h (∼3.3 ppb/h). This change would reduce the number of violation days from 28 to 20% (10%) in a year, mostly in summertime. Concurrent VOC reductions which reduce the production rate of HO x radicals would also be beneficial.