Inorganic composition of fine particles in mixed mineral dust–pollution plumes observed from airborne measurements during ACE‐Asia

Abstract

Chemical characteristics of inorganic water‐soluble aerosol particles measured in large Asian springtime dust events during the Asian Pacific Regional Characterization Experiment (ACE‐Asia) were investigated. Three specific flights (flights 6, 7, and 10) in the Yellow Sea boundary layer with high mineral dust concentrations mixed with pollutants from Asian urban centers are presented. Measurements during a similar campaign, Transport and Chemical Evolution over the Pacific (TRACE‐P), in the same region suggested that fine‐particle ammonium sulfate and nitrate salts, and potassium, apparently from biomass burning, are common particle ionic constituents in polluted air. Observations from the ACE campaign show similar characteristics and found that the main component of water‐soluble mineral dust was Mg 2+ and Ca 2+ . Ion charge balances of measured fine and total aerosol suggest that a significant fraction of the Mg 2+ and Ca 2+ observed were in the form of carbonates. In polluted air mixed with dust that advected directly from large urban regions in roughly half a day to 1 day (flights 6 and 7), much of the fine‐particle nitrate and sulfate (approximately 80%) was apparently associated with ammonium or potassium, the rest likely associated with mineral dust. Only air masses that spent 2–5 days over the Yellow Sea (flight 10) had clear evidence of Cl − depletion. Initial mass accommodation coefficients much less than 0.1 for uptake of SO 2 or HNO 3 by mineral dust in urban plumes containing fossil fuel and biomass‐burning emissions could explain the observations. The data suggest an accommodation coefficient dependence on relative humidity.