Abstract
Biomass burning is an important source of soluble Fe transported to the open ocean; however, its exact contribution remains unclear. Iron isotope ratios can be used as a tracer because Fe emitted by combustion can yield very low Fe isotope ratios due to isotope fractionation during evaporation processes. However, data on Fe isotope ratios of aerosol particles emitted during biomass burning are lacking. We collected size-fractionated aerosol samples before, during, and after a biomass burning event and compared their Fe isotope ratios. On the basis of the concentrations of several elements and Fe species, Fe emitted during the event mainly comprised suspended soil particles in all the size fractions. Iron isotope ratios of fine particles before and after the event were low due to the influence of other anthropogenic combustion sources, but they were closer to the crustal value during the event because of the influence of Fe from suspended soil. Although Fe isotope ratios of soluble Fe were also measured to reduce Fe from soil components, we did not find low isotope signals. Results suggested that Fe isotope ratios could not identify Fe emitted by biomass burning, and low Fe isotope ratios are found only when the combustion temperature is high enough for a sufficient amount of Fe to evaporate.
Highlights
Iron (Fe) in combustion aerosols emitted mainly by human activities exerts various effects on the environment and human health
This study focused on Fe isotope ratios of particles emitted by biomass burning to investigate
Fe isotope ratios can be used as tracers of of Fe aerosol particles from biomass burning
Summary
Iron (Fe) in combustion aerosols emitted mainly by human activities exerts various effects on the environment and human health. The main sources of Fe to the surface ocean are natural aerosols (mainly aeolian dust), dissolution of coastal sediment, and hydrothermal vents [5], whereas Fe in combustion aerosols has been recognized as another possible Fe source due to its high solubility to seawater [6,7,8,9]. Model studies estimate that approximately 30% of atmospheric soluble Fe deposition is from combustion sources, the relative contribution of natural and combustion aerosols to soluble Fe, especially in the open ocean, remains unclear [10]. Iron in combustion aerosols contributes to enhancing the shortwave absorption of solar radiation. Iron oxides emitted by anthropogenic combustions are considered another important source for shortwave absorption, in addition to black and brown carbons [13]
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