1University of California, Irvine, 531 Rowland Hall, Irvine 92697 CA, USA
2University of Miami, RSMAS/MAC, 4600 Rickenbacker Causeway, Miami, 33149 FL, USA
3NASA Langley Research Center, Hampton, 23681 VA, USA
4Max Plank Institute, Atmospheric Chemistry Dept., Johannes-Joachim-Becherweg 27, 55128 Mainz, Germany
5Florida State University, Department of Meteorology, Tallahassee Florida 32306-4520, USA
6NCAR, 1850 Table Mesa Drive, Boulder, 80305 CO, USA
Abstract. We present results from the Intercontinental Chemical Transport Experiment – Phase B (INTEX-B) aircraft mission conducted in spring 2006. By analyzing the mixing ratios of volatile organic compounds (VOCs) measured during the second part of the field campaign, together with kinematic back trajectories, we were able to identify five plumes originating from China, four plumes from other Asian regions, and three plumes from the United States. To identify specific tracers for the different air masses we characterized their VOC composition and we compared their background levels with those obtained during the 2004 INTEX-A mission. The Chinese and other Asian air masses were significantly enhanced in carbonyl sulfide (OCS) and methyl chloride (CH3Cl), while all CFC replacement compounds were elevated in US plumes, particularly HFC-134a.
Although elevated mixing ratios of Halon-1211 were measured in some Chinese plume samples, several measurements at background levels were also observed. After analyzing the VOC distribution and correlations within the Chinese pollution plumes and applying principal component analysis (PCA), we suggest the use of a suite of species, rather than a single gas, as specific tracers of Chinese air masses (namely OCS, CH3Cl, 1,2-dichloroethane, ethyl chloride, and Halon-1211). In an era of constantly changing halocarbon usage patterns, this suite of gases best reflects new emission characteristics from China.