Back to Search Start Over

Changing ozone sensitivity in the South Coast Air Basin during the COVID-19 period.

Authors :
Schroeder, Jason R.
Cai, Chenxia
Xu, Jin
Ridley, David
Lu, Jin
Bui, Nancy
Yan, Fang
Avise, Jeremy
Source :
Atmospheric Chemistry & Physics; 2022, Vol. 22 Issue 19, p12985-13000, 16p
Publication Year :
2022

Abstract

The South Coast Air Basin (SoCAB), which includes the city of Los Angeles and is home to more than 15 million people, frequently experiences ozone (O 3) levels that exceed ambient air quality standards. While strict regulation of O 3 precursors has dramatically improved air quality over the past 50 years, the region has seen limited improvement in O 3 over the past decade despite continued reductions in precursor emissions. One contributing factor to the recent lack of improvement is a gradual transition of the underlying photochemical environment from a VOC-limited regime (where VOC denotes volatile organic compound) towards an NOx -limited one. The changes in human activity prompted by COVID-19-related precautions in spring and summer of 2020 exacerbated these existing changes in the O 3 precursor environment. Analyses of sector-wide changes in activity indicate that emissions of NOx decreased by 15 %–20 % during spring (April–May) and by 5 %–10 % during summer (June–July) relative to expected emissions for 2020, largely due to changes in mobile-source activity. Historical trend analysis from two indicators of O 3 sensitivity (the satellite HCHO/NO2 ratio and the O 3 weekend / weekday ratio) revealed that spring of 2020 was the first year on record to be on average NOx -limited, while the "transitional" character of recent summers became NOx -limited due to COVID-19-related NOx reductions in 2020. Model simulations performed with baseline and COVID-19-adjusted emissions capture this change to an NOx -limited environment and suggest that COVID-19-related emission reductions were responsible for a 0–2 ppb decrease in O 3 over the study period. Reaching NOx -limited territory is an important regulatory milestone, and this study suggests that deep reductions in NOx emissions (in excess of those observed in this study) would be an effective pathway toward long-term O 3 reductions. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
16807316
Volume :
22
Issue :
19
Database :
Complementary Index
Journal :
Atmospheric Chemistry & Physics
Publication Type :
Academic Journal
Accession number :
159798222
Full Text :
https://doi.org/10.5194/acp-22-12985-2022