Source characteristics of oxygenated volatile organic compounds and hydrogen cyanide

Airborne trace gas measurements from Transport and Chemical Evolution over the Pacific (TRACE-P), Pacific Exploratory Mission (PEM)-Tropics B, and Intercontinental Chemical Transport Experiment-North America (INTEX-NA) experiments are analyzed to examine the major source factors contributing to the observed variabilities of oxygenated volatile organic compounds and cyanides. The positive matrix factorization method is applied to coincident measurements of 11 chemicals including CH₃OH, CH₃COCH₃, CH₃CHO, C₂H₂, C₂H₆, i-C₅H₁₂, CO, CH₃C₁, and CHBr₃. Measurements of HCN and CH₃CN are available for TRACE-P and INTEX-NA. We identify major source contributions from the terrestrial biosphere, biomass burning, industry/urban regions, and oceans. Spatial and back trajectory characteristics of these factors are examined. On the basis of TRACE-P and PEM-Tropics B data, we find a factor that explains 80–88% of the CH3OH variability, 20-40% of CH₃COCH₃, 7-35% of CH₃CHO, and 41% of HCN, most likely representing the emissions from terrestrial biosphere. Our analysis suggested that biogenic emissions of HCN may be significant. Cyanogenesis in plants is likely a major emission process for HCN, which was not fully accounted for previously. Larger contributions than previous global estimations to CH₃COCH₃ and CH₃CHO by biomass burning and industry/urban sources likely reflect significant secondary production from volatile organic compound oxidation. No evidence was found for large emissions of CH₃COCH₃ from the ocean. The oceanic CH₃CHO contribution implies large regional variations.