VOC levels in the Los Angeles basin: impact of COVID-19 restrictions

Abstract:

The COVID-19 pandemic offers a unique opportunity to study the impact of reduced activities levels on the air quality of the Los Angeles (LA) Basin. We use data obtained from a sampling campaign carried out at Caltech (Pasadena, CA) where a total of 314 whole air samples were collected from April 16 to July 19, 2020. Canisters were filled up three times a day at 5:30, 9:00, and 14:00 local time in addition to two diurnal profiles carried out on a Sunday (6/14/2020) and Monday (6/15/2020) to analyze daily weekend/weekday trends. The samples were then analyzed with a multi column/detector gas chromatographic system at the laboratory of the University of California, Irvine for carbon monoxide (CO), methane and a wide variety of volatile organic compounds (VOCs) including selected sulfur compounds, halocarbons, selected alkyl nitrates and hydrocarbons. Here we focus on the variation of VOC levels from the beginning of the campaign, when California was under a “stay at home” order, to the end of the sampling period when California transitioned to Phase 3 which allowed the reopening of higher risk work places. We also compare the VOC load to observations from sampling campaigns carried out around the LA basin in recent years (i.e. SARP, CalNex-2010, FIREX-aq 2019 and data collected at Mount Wilson, CA) and evaluate the VOC reactivity. This study can help assess changes in air quality driven by reductions in anthropogenic VOC sources such as vehicular emissions. Reduced activities cause by the COVID-19 pandemic can mimic a scenario where further emission reduction policies are implemented or where vehicular emissions decrease because of a shift in vehicular fleet towards electric cars and trucks.