PNNL

Abstract

The Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) characterized aerosol composition using measurements at Scripps Pier and Mt. Soledad, showing the strong influence of upwind sources as well as influences from semi-volatile components, land-sea breezes, and local traffic. Seasonal patterns and magnitudes of chemical mass concentrations were similar at both sites, with coastal northwesterly back-trajectories occurring 63-65% of the time and bringing below-average submicron mass concentrations. Mass concentrations were above-average for refractory black carbon (rBC) and non-refractory (NR)-organics and nitrate for back-trajectories from urban areas such as Los Angeles--Long Beach. The mass concentrations of NR-organics and non-sea-salt (NSS)-sulfate at Mt. Soledad were correlated strongly (r=0.70-0.71) to those measured at Scripps Pier, but NR-nitrate and NR-ammonium were only moderately correlated (r=0.31-0.57) because their semi-volatility resulted in higher uptake at the higher relative humidity and lower temperatures at Scripps Pier compared to Mt. Soledad. The only significant differences between concentrations during land and sea breezes were for rBC and NR-nitrate. Concentrations of rBC and tracers for brake wear were higher at Mt. Soledad than those measured at Scripps Pier because of traffic on the steep roads surrounding that site, showing that local sources also contribute to observed aerosol composition.