Investigating source origins and photochemical processing of the VOCs during the MINOS-2001 campaign

V. Gros1, J. Williams1, M. Krol2, H. Berresheim3, G. Salisbury1, R. Hofmann1, and J. Lelieveld1

1 Max Planck Institut for Chemistry, Mainz, Germany (vgros@mpch-mainz.mpg.de)
2 Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht University, the Netherlands
3 Deutscher Wetterdienst, Hohenpeissenberg, Germany


During the international MINOS campaign (Creta, August 2001), about 90 air samples were collected in electropolished canisters at the ground based station Finokalia and subsequently analysed by GC-MS in the laboratory. The identified and quantified compounds include various hydrocarbons (propane, butanes, pentanes, benzene), organo halogens (CH3Br, CH3Cl, CH2Cl2, CHCl3, CH3CCl3, CCl4), CFCs (CFC-12, CFC-113, CFC-114, HCFC-22, HCFC-142b). These compounds have a large range of lifetime (a few hours for pentane, several hundred years for CFC-114) and various sources (fossil fuel combustion, biomass burning, ocean). Firstly, we checked the consistency of the dataset from this instrument by using the variability concept. For this purpose, we used the OH mean value measured during the campaign to calculate the lifetime of the most reactive species and we plotted the variability of the different compounds (defined as the standard deviation of their logarithm) against their lifetime. We found that most of the compounds lie on a line with a slope of 0.24. Deviations from the line were interpreted in terms of quality of the measurement on the one hand and in terms of source distribution on the other hand. In particular, we note that the deviations observed for methyl chloroform could be due to still on-going emissions of this compound in some European countries. In addition, 5-day backward trajectories were run every 6 hours for the whole campaign in order to determine the source origins of the observed pollution events and calculations on the ratios of compounds with different lifetimes were performed to investigate the atmospheric photochemical processing.