Daytime CH2O and NO2 observations from MAX-DOAS measurements in Eastern Los Angeles during the COVID-19 Pandemic

Abstract:

Despite continued emission reductions in Southern California, in particular reductions in NO₂ of ~30% observed by the Ozone Monitoring Instrument (OMI) during the COVID-19 pandemic, regular ozone exceedances remain a prevalent issue. To improve our understanding of ozone production during the COVID-19 lockdown period, we examine vertically resolved measurements of ozone precursors, obtained using ground-based Multiple Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) in Whittier, California, ~20 km southeast of downtown Los Angeles. Continuous measurements of CH₂O, NO₂, and aerosol extinction over the spring/summer of 2020 are presented. We observe a reduction of NO₂ of ~20% accompanied by a ~30% reduction in observed CH₂O in the Whittier area compared to observations made during the summer of 2019. Comparisons of MAX-DOAS NO₂ measurements with in-situ measurements from a nearby California Air Resources Board monitoring site and tropospheric NO₂ retrievals from OMI are also discussed.