Trace Gas Measurements Along the Trans-Siberian Railroad: the TROICA Expeditions, 1995 - 2001

Observations of CH4, CO, CO2, O3, NOx, NMHC, 222Rn and standard meteorological parameters have been made along the Trans-Siberian railroad (48.5-58.5oN; 37.7-135.0oE ), Russia. Over the period 1995 - 2001 seven expeditions during different seasons were carried out, and boundary layer air data covering almost 113 000 km were obtained without significant contamination from the train. A secondary CH4 maximum occurs in the annual cycle in summer: highly elevated levels of CH4 were observed in late June - August over the West Siberian lowlands which generally decreased towards East Siberia, except for the far eastern region, where frequent biomass burning events were registered. The isotopic signatures of sampled CH4 point to the wetlands as the dominant source of methane emissions, with some indications of natural gas release. Diurnal variations of 222Rn, CO2 and CH4 due to both micrometeorological conditions and varying soil and vegetation types, were used to estimate ecosystem fluxes of CO2 and CH4. Whilst background CO levels over the west Siberian wetlands were close to background values at mid-to-high northern latitudes, high CO concentrations, exceeding 1000 nmol/mol, were registered east of Chita, as a consequence of forest and other vegetation fires, which significantly affect the chemical composition of the air over Russia. O3 also showed increases in East Siberia and the far eastern region: high night-time O3 values during spring and summer coincided with CO concentration increases. Back-trajectory analyses suggest that boreal forest fires in far eastern Siberia had a significant impact on the observed CO and O3 mixing ratios. >http://www.mpch-mainz.mpg.de/~dunker/Troica/index.htm</a>