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Here, we used a modified single-particle soot photometer (SP2) coupled with a concentric pneumatic nebulizer to measure the size-resolved number and mass concentrations of light-absorbing iron oxide aerosols (FeOx) in liquid water (CNFeOx and CMFeOx, respectively). The SP2 could selectively detect individual FeOx particles in mixed wüstite–fullerene soot laboratory samples and melted Arctic snow samples. The nebulizer efficiency for FeOx particles was about 50% within the 70–650 nm diameter range, as derived from the ratio of the volume of ammonium sulfate before and after extraction by the nebulizer and the size-resolved transmission efficiency in the nebulizer–SP2 sampling line. Uncertainty from the boundary lines empirically drawn to discriminate the scatterplots of FeOx and black carbon in the mixed wüstite–fullerene soot suspensions and snow samples was approximately 3.0% and 10%, respectively. Overall uncertainty in total CNFeOx and CMFeOx (220–1400 nm) was approximately 19% and 18%, respectively. After storage at 4 °C for 16 months, the FeOx particle size distributions in melted Arctic snow had remained stable, and CNFeOx and CMFeOx had changed by less than 19% and 1.0%, on average, respectively. Most of the FeOx on dust particles measured by this system was estimated to be in the diameter range smaller than 1000 nm, considering the nebulizer efficiency for dust particles. The high accuracy of the CNFeOx and CMFeOx measurements will help to improve our quantitative understanding of the wet deposition of FeOx and provide more accurate estimates of the effects of FeOx on snow surface albedo. [ABSTRACT FROM AUTHOR]

Long-term measurements of black carbon (BC) aerosols by filter-based absorption photometers with a heated inlet (COSMOS) in different regions have been useful in elucidating spatial variations and radiative impacts of BC. Evaluations of mass concentrations of BC (MBC) measured by the COSMOS have been made by our previous studies through comparisons with other measurement techniques. However, how variations in the microphysical properties of BC and the co-existing light scattering aerosols affect the COSMOS measurements should be evaluated in more detail. In this study, we assessed these potential effects under various field environments in the Arctic and in the East Asia. From the slopes of the correlation plots between the MBC values measured by the COSMOS and a single-particle soot photometer, the average accuracy of the COSMOS was estimated as ∼10% in the MBC range 1–3000 ng m−3. On an hourly basis, the estimated sensitivity of the COSMOS MBC values to the changes in the BC size distributions was less than 10%, within the typical variabilities of BC size at individual observation sites. The COSMOS measurements depended little on the mixing states of BC and the concentrations of co-existing light scattering aerosols, except in the maritime air masses of East Asia, where the relative abundance of sea salt to BC was very high. The MBC measured by COSMOS also well agreed with elemental carbon measurements. Our results demonstrate the high reliability of COSMOS measurements under various environments. Copyright © 2019 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]