Abundance and Fractional Solubility of Aerosol Iron During Winter at a Coastal City in Northern China: Similarities and Contrasts Between Fine and Coarse Particles

Abstract

AbstractAerosol deposition is a major source of soluble Fe in open oceans, affecting marine biogeochemistry and primary production. However, Fe fractional solubility, a key parameter in estimating deposition fluxes of soluble aerosol Fe, is still highly uncertain. Abundance and fractional solubility of aerosol Fe in fine (<1 μm) and coarse (>1 μm) particles was measured at Qingdao (a coastal city in northern China) in November‐December 2019. Average concentrations of total and soluble Fe were found to be 798 ± 466 and 7.7 ± 14.5 ng/m3 in coarse particles, and 801 ± 534 and 7.3 ± 7.6 ng/m3 in fine particles. Fe solubility was significantly lower in coarse particles (average: 0.80 ± 1.03%) than fine particles (average 1.29 ± 1.41%). Compared to clean days, total Fe concentration was substantially increased during dust and haze days; however, Fe solubility was significantly reduced in dust days and elevated in haze days. Acid processing significantly enhanced Fe solubility in both fine and coarse particles, and the contribution of primary emission to Fe solubility enhancement was important for fine particles but minor for coarse particles. Higher Fe solubility (>1%) in fine and coarse particles was usually observed at high aerosol acidity (pH < 4) and high RH (>60%), suggesting critical roles of aerosol acidity and water content in regulating aerosol Fe solubility.