UC San Diego

Fine particulate matter (PM2.5) is a mixture of microscopic solid particles and liquid droplets that pose significant health risks due to their ability to penetrate deep into the respiratory system. In recent decades, several studies have examined the relationships between air pollution and various meteorological factors, such as surface temperature, relative humidity, wind, and precipitation. Among these factors, precipitation can effectively remove PM2.5 and other airborne particles from the atmosphere through processes such as scavenging and wet deposition. Most studies focusing on the relationship between precipitation and PM2.5 have been conducted in regions affected by monsoon rains. This current work investigated the impact of precipitation patterns on PM2.5 concentrations in Los Angeles (LA) County, the most populous county in the United States, over twenty years (2003 to 2022). This study analyzed daily precipitation, PM2.5 concentrations, and atmospheric rivers (AR) to look at the impact on PM2.5 pollution by extreme precipitation events in a region characterized by a Mediterranean climate. The results of a moving window correlation analysis at different locations within LA County showed that PM2.5 concentrations and precipitation are inversely related, for the most part, particularly during wet winters. A matching analysis between days with precipitation above a given threshold and control days showed that PM2.5 tended to decrease the day of and the day after a precipitation event. The findings of this study can help understand the spatial heterogeneity of the relationship between precipitation and PM2.5 pollution in Southern California and the potential implications for public health in a changing climate.