Sources of Pollution and Interrelationships Between Aerosol and Precipitation Chemistry at a California Coastal Site

This study examines co-located aerosol and precipitation chemistry data between 2010-2016 at Pinnacles National Monument ~65 km east of the coastline in Central California. Positive matrix factorization analysis of the aerosol composition data revealed seven distinct pollutant sources: aged sea salt (25.7% of PM2.5), biomass burning (24.2% of PM2.5), fresh sea salt (15.0% of PM2.5), secondary sulfate (11.7% of PM2.5), dust (10.0% of PM2.5), vehicle emissions (8.2% of PM2.5), and secondary nitrate (5.2% of PM2.5). The monthly profile for all seven factors is discussed, with meteorology and transport playing key roles. While concentrations of PM2.5 have increased during the study period, only secondary sulfate exhibited a statistically significant change (a reduction) over time among the PM2.5 source factors. In contrast, PMcoarse increased most likely due to dust influence. Concentration Weighted Trajectory (CWT) maps illustrate the most important source regions for the seven PMF source factors based on the season. For example, locally generated dust is more important in fall months (September-October) whereas long-range transport from areas such as Asia are more influential in the spring months (March-May). Monthly profiles of precipitation chemistry are summarized showing that the most abundant species were SO42-, NO3-, and Cl-. Intercomparisons between the precipitation and aerosol data revealed several features: (i) precipitation pH was inversely related to factors associated with more acidic aerosol constituents such as secondary sulfate and aged sea salt, in addition to being reduced by uptake of HNO3 in the liquid phase; (ii) two aerosol source factors (dust and aged sea salt) and PMcoarse exhibited a positive association with Ca2+ in precipitation, suggestive of directly emitted aerosol types with larger sizes promoting precipitation; and (iii) sulfate levels in both the aerosol and precipitation samples analyzed were significantly correlated with dust and aged sea salt PMF factors, pointing to the partitioning of secondary sulfate to dust and sea salt particles. The results of this work have implications for the region’s air quality and hydrological cycle, in addition to demonstrating that the use of co-located aerosol and precipitation chemistry data can provide insights relevant to aerosol-precipitation interactions.