Atmospheric Inversions and Fine Particulate Pollution in Southern California

Air pollution levels vary dramatically across regions and seasons, and many areas in the world experience severe air pollution particularly during the winter. Though several physical atmospheric variables (e.g., temperature, humidity, wind) can influence air pollution patterns, low-level thermal inversions play a critical role by increasing the vertical stability of the lower atmosphere and thus inhibiting vertical mixing in the affected regions. Inversions vary widely in seasonality, frequency, and intensity across locations and, strong inversions have been associated with severe pollution events. Additionally, several studies have linked the occurrence of temperature inversions to health effects. Characterizing the associations between thermal inversions and PM2.5 can inform policies that curb emissions and disseminate information about risks to public health during inversion episodes. Here we study the association between daily levels of PM2.5 in Southern California and temperature inversions spanning 2006-2019. Our main aim was to quantify the effects of inversion characteristics, such as inversion strength and height, on the seasonal patterns of PM2.5 concentrations in the region. Overall, our study confirms the magnifying effects of temperature inversions on the concentrations of PM2.5 in the study area, particularly in wintertime. Our results suggest that temperature inversions should be considered as triggers for severe air pollution events in policies associated with impacts on public health, as well as in the development of improved early warning systems.