Emissions and meteorological impacts on PM species concentrations in Southern California using generalized additive modeling.

The chemical composition of PM has a significant impact on human health and air quality, and its accurate knowledge can be used to identify contributing emission sources. Assessing and quantifying the impacts of various factors (e.g., emissions, meteorology, and large-scale climate patterns) on the main PM chemical components can give guidance for implementing effective regulations to improve air quality in the future. In this study, we developed generalized additive models (GAMs) to assess how emissions, meteorological factors, and large-scale climate indices affected ammonium, sulfate, nitrate, elemental carbon, and organic carbon from 2002 to 2019 in the South Coast Air Basin (SoCAB). Concentration trends from three sites in the SoCAB are studied. The statistical results showed that GAMs can capture the variability of these species' daily concentrations (R = 0.6 to 0.7) and annual concentrations (R = 0.93 to 0.99). Precursor emissions most significantly affect PM species production, though meteorological factors like maximum temperature, relative humidity, wind speed, and boundary layer height, also influence PM composition. In the future, these meteorological factors will become more significant in affecting PM speciation, although emissions will continue to strongly affect formation. Results show that the composition of most PM species will decrease in the future except for OC, which will become the largest contributor to PM.