Influence of Anthropogenic Emission Reduction during COVID-19 on Black Carbon in California’s South Coast Air Basin

Abstract:

Black carbon (BC) is a light-absorbing particle in the air that is emitted into the atmosphere from human activities and natural processes. The main sources of anthropogenic emissions in California are mobile sources, stationary generators, and residential fireplaces and woodstove. Different sources can produce BC particles with varying physical and compositional characteristics, which has implications for both health and climate. Due to the severe consequences of ambient BC, diesel particulate matter or DPM, which is a subset of BC, has been regulated heavily under California’s mobile source emission control measures. BC emission reduction is also motivated by the state’s short-lived-climate pollutant (SLCP) strategy set to reduce anthropogenic BC emissions by 50% below 2013 levels by 2030. Tracking the effectiveness of BC mitigation measures are critical for realizing the progress made under these programs. The reduced human activities, particularly on-road mobile sources, during the COVID-19 shelter-in-place order (Executive Order N-33-20) provided a natural experiment to evaluate current and future BC emission reduction pathways in the state.

This study presents the multi-wavelength ambient BC and carbon monoxide (CO) measurements made at the Mount Wilson Observatory (MWO), California. These measurements were used to estimate the changes in regional BC emissions after the shelter-in-place order in Los Angeles County within the South Coast Air Basin (SCLA). Furthermore, BC contributions from fossil fuel combustion and biomass burning were estimated by applying Angstrom exponent based source attribution calculations on the multi-wavelength BC data. The results indicated that both emission control measures for fossil fuel combustion and biomass burning are necessary strategies in moving toward achieving emission reduction goals over the next decade.