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

Abstract

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.

Long-term measurements (2010–2014) of carbonaceous aerosol and carbon monoxide at the Zotino Tall Tower Observatory (ZOTTO) in central Siberia

“…The obtained WSOC / OC ratio is typical for non-urban sites surrounded by pine forest. It has been documented that in the summer season aged secondary organic aerosols produced by monoterpene oxidation as well as biomass burning organic particulate matter contain a high fraction of WSOC, ranging from 0.5 to 0.8 (Saxena et al, 1995;Kiss et al, 2002;Pöschl, 2005;Pio et al, 2007;Timonen et al, 2008). Table 1 also provides summary statistics for carbonaceous species at ZOTTO compared with those reported for highaltitude remote sites.…”

“…Given the low CO concentration, a measurable pollution input from the fires is not to be expected. In addition, any biomass burning aerosol that may have been transported in the boundary layer (Table 5, columns 1 and 2) could have been effectively removed via precipitation (APT = 7.3 mm) (Kanaya et al, 2016;Ohata et al, 2016). Figure 12c shows that precipitation with different intensity occurred along the air mass trajectories before they reached the measuring site.…”

“…The strength of the correlation between EC and CO strongly depends on the meteorological conditions. Wet deposition can affect aged EC Verma et al, 2011;Kanaya et al, 2016) but not CO, while CO can be removed from the atmosphere by oxidation with OH radicals (Hamilton et al, 2014). In addition, as noted above, CO can be produced from the oxidation of methane and non- Meadow-grass straw, wheat straw 10.9 ± 1.5 (F) 5.4 ± 4.3 (F) Dhammapala et al (2007b) a TOT (TOR) -thermal-optical transmittance (reflectance).…”

“…The NCEP/NCAR meteorological data set was also used to estimate the mixing layer depth (MLD) and accumulated precipitation along the trajectory (APT). We used the APT data as a measure of wet removal of aged carbonaceous species (Kondo et al, 2011a;Matsui et al, 2011;Kanaya et al, 2016). In some cases, the APT values were averaged by dividing the total precipitation along all the trajectories for a selected time period by the number of these trajectories (Table 4).…”

Tagged tracer simulations of black carbon in the Arctic: transport, source contributions, and budget

“…For East Asia, we used BC data at nine rural and remote sites in China during 2006 and 2007 from Zhang et al (2012). In addition, we used measurements at Fukue Island, a remote site located in western Japan (Kanaya et al, 2016). For North America, the data from the IMPROVE network for 2007-2011 were used (http://views.cira.colostate.edu/fed).…”