An Examination of the Impact of Local Shelter-in-Place Orders on Atmospheric Aerosol Mass and Chemical Composition in Boulder Colorado During the COVID-19 Pandemic

The COVID-19 pandemic has caused large segments of regional populations to shelter-in-place, resulting in decreased atmospheric emissions from transportation and industry. As an example, dramatic reductions in nitrogen dioxide were clearly visible in highly publicized satellite images. These and other lower emissions have the potential to affect air quality depending on the local conditions such as prior historical pollutant levels, seasonality, and meteorology. Here we focus on ground-based measurements of aerosol mass and chemical composition along with trace gas species made in Boulder Colorado during the spring and early summer of 2020 when local shelter-in-place orders were in effect and then slowly lifted. Additional measurements were made later in the summer at a time when ozone pollution levels typically peak in the region. Chemical markers from various sources and secondary chemical reactions in the aerosol and gas phase mass spectra are explored using positive matrix factorization. This combined dataset is used to examine the impact of the local reduced anthropogenic emissions on the mass and chemical composition of aerosol particles.