Impact of Wildfire Emissions on Chloride and Bromide Depletion in Marine Aerosol Particles.

This work examines particulate chloride (Cl(-)) and bromide (Br(-)) depletion in marine aerosol particles influenced by wildfires at a coastal California site in the summers of 2013 and 2016. Chloride exhibited a dominant coarse mode due to sea salt influence, with substantially diminished concentrations during fire periods as compared to nonfire periods. Bromide exhibited a peak in the submicrometer range during fire and nonfire periods, with an additional supermicrometer peak in the latter periods. Chloride and Br(-) depletions were enhanced during fire periods as compared to nonfire periods. The highest observed %Cl(-) depletion occurred in the submicrometer range, with maximum values of 98.9% (0.32-0.56 μm) and 85.6% (0.56-1 μm) during fire and nonfire periods, respectively. The highest %Br(-) depletion occurred in the supermicrometer range during fire and nonfire periods with peak depletion between 1.8-3.2 μm (78.8% and 58.6%, respectively). When accounting for the neutralization of sulfate by ammonium, organic acid particles showed the greatest influence on Cl(-) depletion in the submicrometer range. These results have implications for aerosol hygroscopicity and radiative forcing in areas with wildfire influence owing to depletion effects on composition.