Abstract
The impact of wildfires on surface air composition over central Siberia is investigated based on near-surface carbon monoxide (CO) measurements conducted at Zotino Tall Tower Observatory (ZOTTO), a remote station in the center of Siberia, during 2007 and 2008 warm seasons. Seasonal variations of intensity and spatial distribution of wildfires in south of western and eastern Siberia are found to be important factors contributing a substantial part of synoptic and year-to-year variability of background CO levels in the region. Based on the MODIS area burned product, the estimate of the total yearly CO emitted from wildfires in the regions potentially affecting the measurement site (those of European Russia and Siberia) is approximately 15 and 27 Tg CO in 2007 and 2008, versus 18.0 and 39.4 Tg CO from wildfires in all of Russia in 2007 and 2008, and 11 Tg CO from all anthropogenic sources in Russia according to EDGARv4.1 database for year 2005. The severe fire activity in northern Eurasia, particularly in western Siberia, during 2008 caused enhanced springtime surface CO levels observed at ZOTTO, with median CO mixing ratio in April-May 2008 by approximately 15 ppb higher compared to April-May 2007. Episodes of air transport from wildfires upwind of the measurements site are identified based on ensembles of backward trajectories and MODIS products. The impact of distinct wildfire smoke plumes on near-surface CO mixing ratios, along with the influence of wildfire and anthropogenic emissions on background CO levels in the region is estimated using backward Lagrangian trajectory statistics. The estimated relative CO enhancement in fire plumes with transport times up to 2 days is about 5-25 ppb in springs 2007 and 2008, and 50 ppb in summer 2008, based on the observed median values, with a maximal absolute value of 250 ppb observed in April 2008. Boreal forest fires over the vast areas of central Siberia along with regional anthropogenic sources are found to be the major factors driving short-term (synoptic) variability of near-surface CO during the warm season.