Abundances and Microphysical Properties of Light-Absorbing Iron Oxide and Black Carbon Aerosols Over East Asia and the Arctic

Black carbon (BC), brown carbon, and light-absorbing iron oxides (FeO_x) aerosols affect Earth's energy budget through their strong absorption of solar radiation. FeO_x aerosols can also affect global biogeochemical cycles through their role as a nutrient for oceanic phytoplankton. However, observational data for these aerosols required for evaluating their effects using global models are scarce, especially for FeO_x. Here, we summarize and compare the data sets of BC and FeO_x from five ground-based and three aircraft observation campaigns conducted in the East Asian and Arctic regions during the 2009–2018 period acquired using a modified single-particle soot photometer. In these campaigns, >80% of FeO_x-containing aerosols in the 170–270 nm FeO_x core size range had microphysical features indicating an anthropogenic origin. The particle size distribution for each of the BC and FeO_x was similar in all of the data sets except for those dominated by fresh urban pollution or pristine Arctic air. The campaign-averaged mass concentrations of FeO_x and BC were ~60–360 ng/m³ and ~240–1,300 ng/m³, respectively, in East Asia, and ~6 ng/m³ and ~20–30 ng/m³, respectively, in the Arctic. The campaign-averaged FeO_x/BC mass concentration ratio varied within a narrow range of 0.2–0.6 in both East Asian and Arctic regions. In every campaign, FeO_x, BC, and carbon monoxide were tightly correlated with each other with similar slope to the urban campaigns (around Tokyo), implying the spatiotemporal variation of anthropogenic FeO_x emission around northern middle-to-high latitudes is similar to those of anthropogenic BC and CO emissions.