Measurements of organic and elemental carbon in Asian outflow during ACE‐Asia from the NSF/NCAR C‐130

Abstract

During the spring 2001 Asian Pacific Regional Aerosol Characterization Experiment (ACE‐Asia) intensive observation period, we measured elemental and organic carbon (EC and OC) from the National Science Foundation/National Center for Atmospheric Research (NSF/NCAR) C‐130 aircraft. Samples were collected on quartz filters using a Particle Concentrator–Brigham Young University Organic Sampling System (PC‐BOSS) to minimize positive and negative artifacts and analyzed using a Sunset Labs thermal/optical analyzer. Although short aircraft sampling times limited our sensitivity, total carbon (EC plus OC) was quantifiable on all but one level flight leg. We could not confidently apportion total carbon (TC) between EC and OC on about a quarter of the legs, mostly in the free troposphere (FT). About a third of the samples showed significant evaporation of collected aerosols from their quartz filter (a median of 20% on these samples), while a similar number had too little evaporation to detect. We found that TC and OC concentrations were generally higher in the boundary layer (medians of 7.6 μg TC/m3 and 5.8 μg OC/m3) than in the free troposphere (medians of 3.1 μg TC/m3 and 3.9 μg OC/m3, the latter from only a few samples). The same appears to be true for EC, but the free troposphere (FT) statistics for EC are also poor. Average concentrations were somewhat higher than the medians, reflecting the impact of a few more polluted samples. OC was much more variable than was EC. In the FT the TC to non‐sea‐salt sulfate ratio ranged from 3.2 to 6.0, so carbonaceous aerosols were considerably more concentrated than non‐sea‐salt sulfate in the upper troposphere. When dust mass was included, organic matter ranged from about 0.1 to 0.7 of the fine particle mass. TC/EC ratios ranged from 2 to 15, with medians of ∼4–5. Air in the Yellow Sea, the Korea Strait, and the Sea of Japan had generally higher concentrations of OC than that in the East China Sea or the Pacific south and east of Japan.