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Analysis of the troposphere composition changes over Russia

Final Activity Report Summary - ANCORUS (Analysis of the troposphere composition changes over Russia)

In order to study the origin and behaviour of atmospheric constituents in the boundary layer over Russia several data sets were employed, namely the data on methane (CH4) and carbon monoxide (CO), based on both continuous measurements and air samples. Data was derived from surveys along the trans-Siberian railway, i.e. the TROICA project, for the period 1996-2005, from continuous measurements of the surface ozone concentrations at Kislovodsk high mountain station (KHMS) for the period 1990-2006 as well as from some other sources.

It was shown that the distribution of CO across Russia had large-scale spatial gradients which were defined by anthropogenic sources over European Russia and central Siberia and biomass burning in the Far East. Based on the analysis of CO concentration, radiocarbon (14C) and stable isotope (13C and 18O) content of CO which were determined in air samples during the summer of 1999, it was found that sources of CO along the Ob appeared to be connected to methane oxidation based on an inferred source delta-13C, of value equal to -36.8±0.6‰, while the value for source delta-18O, which was approximately 9.0±1.6‰, identified it as burning. Thus, flaring in the oil and gas production could be supposed to be a source. Along the trans-Siberian railroad background CO was to various degrees contaminated with CO from methane combustion.

The distribution of atmospheric methane across Russia was affected by large-scale wetland emissions in western Siberia and numerous small scale anthropogenic sources. The source isotopic signature of the samples collected in Western Siberia in summer 1999, with delta-13C being equal to -62.9±0.7 ‰ and delta-D showing a value of -369±11 ‰, confirmed that biogenic methane from wetlands dominated the substantial CH4 excess in the region. The biogenic methane source was found to be also prevailing during summer 2001. During the spring expedition numerous anthropogenic sources, such as natural gas leaks and coal mining, were detected. The obtained results were compared with TM3 simulated methane isotopic composition. In the base emission scenario either the contribution of the biogenic source to the observed 13C(CH4) and D(CH4) levels was underestimated or the contribution of anthropogenic sources was overestimated, probably due to low model spatial resolution. In the test scenario we increased the Siberian bogs emission by 50 %, which led to improved agreement between source isotopic signature, both for 13C(CH4) and D(CH4), which was estimated for the modelled and measured datasets.

Unlike to the observed increase of the background ozone concentration in Europe, we reported a substantial decrease of the background ozone concentration at Kislovodsk high mountain station in the Caucasus (KHMS, 43.7N 42.7E 2070 m above sea level) with the rate of -0.91±0.17 ppb/year for the period from 1991 to 2001 and -0.37±0.14 ppb/year for the period from 1997 to 2006. Utilising the ‘LAGRANTO’ trajectory tool we came to the conclusion that KHSM was strongly influenced by a considerable emission decrease in the early 1990s in former USSR and by emissions regulations in Western Europe, causing decrease of ozone concentration. For the period from 1997 to 2006 the ozone trend at KHMS was controlled by a slight emission increase in the region. The negative trend which was observed at the station was not reproduced by two global chemistry transport models, namely the ECHAM5-MOZ and LMDz-INCA. The poor representation of the mixing in PBL and the stratosphere-troposphere exchange should be mentioned among the reasons of this discrepancy. The overestimated photochemical production also seemed to be one of the drawbacks of the global models, probably due to their low spatial resolution, related to unresolved topography and emissions averaging.

The general features of the seasonal cycle of surface ozone were obtained for extra-tropical latitudes, using 114 stations worldwide. We found that the spring maximum was likely to be of dynamical and transport rather than photochemical origin. The identified features were compared with the corresponding data from the ECHAM5/MESSy1 model, developed between 1998 and 2005. Finally, for the model clusters that covered rural and semi-polluted sites the role of the photochemical production and destruction seemed to be overestimated.