Abstract
Siberia with its large area covered with boreal forests, wetlands and tundra is believed to be an important sink
for ozone via dry deposition and reactions with biogenic volatile organic compounds (BVOCs) emitted by the
forests. To study the importance of deposition of ozone in Siberia, we analyse measurements of ozone mixing
ratios taken along the Trans-Siberian railway by train, air-borne measurements andpoint measurements at
the Zotino station. For all data, we ran the Lagrangian particle dispersion model FLEXPART in backward
mode for 20 d, which yields the so-called potential emission sensitivity (PES) fields. These fields give a
quantitative measure of where andhow strongly the sampledair masses have been in contact with the surface
and hence possible influenced by surface fluxes. These fields are further statistically analysed to identify
source andsink regions that are influencing the observedozone. Results show that the source regions for the
surface ozone in Siberia are located at lower latitudes: the regions around the Mediterranean Sea, the Middle
East, Kazakhstan andChina. Low ozone mixing ratios are associated to transport from North West Russia,
the Arctic region, andthe Pacific Ocean. By calculating PES values for both a passive tracer without
consideration of removal processes and for an ozone-like tracer where dry deposition processes are included,
we are able to quantify the ozone loss occurring en route to the receptor. Strong correlations between low
ozone concentrations andthe spatially integratedfootprints from FLEXPART, especially during the period
summer to autumn, indicate the importance of the Siberian forests as a sink for tropospheric ozone.
