Articles | Volume 16, issue 16
Atmos. Chem. Phys., 16, 10689–10705, 2016
Atmos. Chem. Phys., 16, 10689–10705, 2016

Research article 30 Aug 2016

Research article | 30 Aug 2016

Long-term observations of black carbon mass concentrations at Fukue Island, western Japan, during 2009–2015: constraining wet removal rates and emission strengths from East Asia

Yugo Kanaya1,2, Xiaole Pan3,4, Takuma Miyakawa1,2, Yuichi Komazaki1, Fumikazu Taketani1,2, Itsushi Uno4, and Yutaka Kondo5 Yugo Kanaya et al.
  • 1Department of Environmental Geochemical Cycle Research, Japan Agency for Marine-Earth Science and Technology, Yokohama, Kanagawa 2360001, Japan
  • 2Institute of Arctic Climate and Environmental Research, Japan Agency for Marine-Earth Science and Technology, Yokohama, Kanagawa 2360001, Japan
  • 3Institute of Atmospheric Physics/Chinese Academy of Sciences, State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Beijing, 100029, China
  • 4Research Institute for Applied Mechanics, Kyushu University, Kasuga, 816–8580, Japan
  • 5National Institute of Polar Research, Tachikawa 1908518, Japan

Abstract. Long-term (2009–2015) observations of atmospheric black carbon (BC) mass concentrations were performed using a continuous soot-monitoring system (COSMOS) at Fukue Island, western Japan, to provide information on wet removal rate constraints and the emission strengths of important source regions in East Asia (China and others). The annual average mass concentration was 0.36 µg m−3, with distinct seasonality; high concentrations were recorded during autumn, winter, and spring and were caused by Asian continental outflows, which reached Fukue Island in 6–46 h. The observed data were categorized into two classes, i.e., with and without a wet removal effect, using the accumulated precipitation along a backward trajectory (APT) for the last 3 days as an index. Statistical analysis of the observed ΔBC ∕ ΔCO ratios was performed to obtain information on the emission ratios (from data with zero APT only) and wet removal rates (including data with nonzero APTs). The estimated emission ratios (5.2–6.9 ng m−3 ppb−1) varied over the six air mass origin areas; the higher ratios for south-central East China (30–35° N) than for north-central East China (35–40° N) indicated the relative importance of domestic emissions and/or biomass burning sectors. The significantly higher BC ∕ CO emission ratios adopted in the bottom-up Regional Emission inventory in Asia (REAS) version 2 (8.3–23 ng m−3 ppb−1) over central East China and Korea needed to be reduced at least by factors of 1.3 and 2.8 for central East China and Korea, respectively, but the ratio for Japan was reasonable. The wintertime enhancement of the BC emission from China, predicted by REAS2, was verified for air masses from south-central East China but not for those from north-central East China. Wet removal of BC was clearly identified as a decrease in the ΔBC ∕ ΔCO ratio against APT. The transport efficiency (TE), defined as the ratio of the ΔBC ∕ ΔCO ratio with precipitation to that without precipitation, was fitted reasonably well by a stretched exponential decay curve against APT; a single set of fitting parameters was sufficient to represent the results for air masses originating from different areas. An accumulated precipitation of 25.5 ± 6.1 mm reduced the TE to 1∕e. BC-containing particles traveling to Fukue must have already been converted from hydrophobic to hydrophilic particles, because the behavior of TE against APT was similar to that of PM2.5, the major components of which are hydrophilic. Wet loss of BC greatly influenced interannual variations in the ΔBC ∕ ΔCO ratios and BC mass concentrations. This long-term data set will provide a benchmark for testing chemical transport/climate model simulations covering East Asia.

Short summary
Wet removal of atmospheric black carbon particles was quantitatively characterized in terms of accumulated precipitation along a backward trajectory (APT) using long-term observations at Fukue Island, western Japan, receiving Asian continental outflow with variable degrees of influence from precipitation. The emission inventory of BC over East Asia was assessed in terms of the observed BC/CO ratios. Model simulations should be diagnosed with these improved knowledge on the emission and removal.
Final-revised paper