Measurement of Light-absorbing Iron Oxide Aerosols in Liquid Water with a Modified Single-Particle Soot Photometer

TATSUHIRO MORI, Yutaka Kondo, Kumiko Goto-Azuma, Nobuhiro Moteki, Atsushi Yoshida, Kaori Fukuda, Yoshimi Ogawa-Tsukagawa, Sho Ohata, Makoto Koike, Keio University

     Abstract Number: 61
     Working Group: Aerosols, Clouds and Climate

Abstract
We used a single particle soot photometer (SP2) with a CETAC Marin-5 nebulizer to measure size-resolved mass and number concentrations of light-absorbing iron oxide aerosols (FeO_x) in liquid water (C_MFeOx and C_NFeOx, respectively). The SP2 could selectively detect individual FeO_x particles in a wüstite reference sample and several melted Arctic snow samples. The nebulizer efficiency (ε) for FeO_x particles was about 50% within 70–650 nm diameter range, derived from the ratio of volume of ammonium sulfate before and after extraction of the nebulizer and the size-resolved transmission efficiency in the nebulizer–SP2 sampling line. We corrected the size-resolved C_MFeOx at particle diameters larger than 920 nm by using the removal efficiency, which was defined as the ratio of the size-resolved number concentration of FeO_x in hydrometeors to that in air measured at Fukue Island in spring. The uncertainty due to the correction was approximately 10% for C_MFeOx and negligibly small for C_NFeOx. The uncertainty from differences in the boundary lines used to discriminate between FeO_x and black carbon was also approximately 10%. The overall uncertainties in the total C_MFeOx and C_NFeOx (220–1200 nm) were approximately 19% and 20%, respectively. We demonstrated that during 16-month storage periods, the FeO_x size distributions in water were stable, and C_MFeOx and C_NFeOx changed less than 1.0% and 19% on average, respectively. The high accuracy of the C_MFeOx and C_NFeOx measurements is indispensable to quantitatively understand the wet deposition of FeO_x and accurately estimate the effect of FeOx on snow surface albedo.