title: The annual course of TCA formation in the lower troposphere: a modeling study.
abstract: We present a modeling study investigating the influence of climate conditions and solar radiation intensity on gas-phase trichloroacetic acid (TCA) formation. As part of the ECCA-project (Ecotoxicological Risk in the Caspian Catchment Area), this modeling study uses climate data specific for the two individual climate regimes, namely "Kalmykia" and "Kola Peninsula". A third regime has also been included in this study, namely "Central Europe", which serves as a reference to somehow more moderate climate conditions. The simulations have been performed with a box modeling package (SBOX, photoRACM), which uses Regional Atmospheric Chemistry Mechanism (RACM) as its chemistry scheme. For this model a mechanism supplement has been developed including the reaction pathways of methyl chloroform photooxidation. The investigations are completed by a detailed sensitivity study addressing the impact of temperature and relative humidity. Atmospheric OH and HO2 concentrations and the NOx/HO2 ratio were identified as the governing quantities controlling the TCA formation trough methyl chloroform oxidation in the gas phase. Model calculations show a TCA production rate ranging between almost zero and 6.5 x 10(3) molecules cm(-3) day(-1) depending on location and season. In the Kalmykia regime the model predicts mean TCA production rates of 1.3 x 10(-4) and 5.4 x 10(-5) microg m(-3) year(-1) for the urban and rural environment, respectively. From the comparison of model calculations with measured TCA burdens in the soil ranging between 130 g m(-3) and 1750 g m(-3) we conclude that TCA formation through methyl chloroform photooxidation in the gas-phase is probably not the principal atmospheric TCA source in this region.
authors.affiliation: Institute for Geophysics, Astrophysics, and Meteorology (IGAM), Karl-Franzens-University Graz, Universitaetsplatz 5, A-8010 Graz, Austria. folberth@lsce.saclay.cea.fr
authors.forename: Gerd
authors.initials: G
authors.lastname: Folberth
authors.forename: Gabriele
authors.initials: G
authors.lastname: Pfister
authors.forename: Dietmar
authors.initials: D
authors.lastname: Baumgartner
authors.forename: Erich
authors.initials: E
authors.lastname: Putz
authors.forename: Ludwig
authors.initials: L
authors.lastname: Weissflog
authors.forename: Nikolai P
authors.initials: NP
authors.lastname: Elansky
mesh_terms: D000393:Air Pollutants / Q000737:chemistry*; D000397:Air Pollution; D002980:Climate; D005060:Europe; D005740:Gases; D006838:Hydrocarbons / Q000737:chemistry; D008956:Models, Chemical; D019445:Solar Activity; D014238:Trichloroacetic Acid / Q000737:chemistry*
chemical_list: D000393:Air Pollutants; D005740:Gases; D006838:Hydrocarbons; D014238:Trichloroacetic Acid