Aerosol Particle Processing and Removal by Fogs: Observations in Chemically Heterogeneous Central California Radiation Fogs

Fog composition and deposition fluxes of fog water and fog solutes were measured in six radiation fog events in San Joaquin Valley, California during winter 1998/1999. Measurements made at 2 hr intervals with 0.30 m2 and 0.06 m2 Teflon deposition plates yielded excellent reproducibility (relative standard deviations of 3.8–6.0%) for water, nitrate, sulfate and ammonium. Water fluxes measured at 5 min intervals with a recording balance agreed well with the deposition plate measurements before 8:00 AM. After 8:00 AM evaporation proved problematic. The average deposition velocity from the study for fog nitrate (3.8 cm s−1) was less than those for fog sulfate (5.1 cm s−1) and ammonium (6.7 cm s−1). All three species generally exhibited smaller deposition velocities than fog water. The species dependent trend in deposition velocities was consistent with preferential enrichment of these species in small fog drops (nitrate > sulfate > ammonium).