Comparison of Black Carbon Mass Concentrations Observed by Multi-Angle Absorption Photometer (MAAP) and Continuous Soot-Monitoring System (COSMOS) on Fukue Island and in Tokyo, Japan
Abstract:Reducing uncertainties associated with measurements of black carbon (BC) particles is critical for improved quantification of their impacts on climate and health. We compared BC measurements using a continuous soot-monitoring system (COSMOS) and a multi-angle absorption photometer (MAAP) to assess their uncertainties. We found that measurements by COSMOS and MAAP instruments correlate strongly to each other, and their hourly ratio showed minimal temporal variations, but the MAAP values were systematically higher by a factor of 1.56 ± 0.19 (1σ), based on simultaneous observations on Fukue, a remote island in Japan, for about a year. This factor was almost independent of the air mass origins and seasons. Measurements in central Tokyo for about 2 months also yielded a similar relationship, with a systematic difference factor of ∼1.8. It is likely that the systematic differences are caused by differences in the conditions/protocols in the thermal/optical BC determinations used for calibration of each optical instrument. Based on results from the COSMOS instrument calibrated using an elemental carbon and organic carbon analyzer with thermal/optical transmittance correction, the MAAP absorption cross section (6.6 m2 g−1) needs to be systematically increased to 10.3 m2 g−1 at 639 nm for Fukue when b abs values derived from the built-in software are used. Small temporal fluctuations in the ratios of MAAP-derived BC to COSMOS-derived BC were possibly caused by humidity effects and temporal variations in the optical properties of the measured particles. For MAAP, we also found that low filter-transmittance (0.2–0.5) could either increase or decrease the BC reading. The current best recommendations with the MAAP instrument are to use an increased cross section, to use data with high filter-transmittance (>0.5) only, and to control humidity.
Copyright 2012 American Association for Aerosol Research
Document Type: Research Article
Affiliations: 1: Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama,Kanagawa, Japan 2: Department of Earth and Planetary Science, Graduate School of Science,The University of Tokyo, Tokyo, Japan
Publication date: January 1, 2013