Trans-Eurasian transport of ozone and its precursors

Long-range transport of air across the European and Asian continents brings substantial quantities of ozone and other oxidants to northeast Asia from upwind sources over Europe and North America. This transport differs significantly from that over the Pacific and Atlantic Oceans because of weaker and less frequent frontal systems over the continent and because of weaker convective lifting over European sources. Slower O-3 formation, faster destruction at low altitudes, and greater deposition over continental regions lead to Europe having a smaller impact on O-3 than other source regions. We present chemical transport model studies of the formation and transport of O3 from European precursor sources and investigate the extent of their impacts over Eurasia. We focus on measurement sites at 100degreesE, representing the inflow to east Asia on which regional pollutant sources build, and on northeast Asia, which may be directly affected by transport across Eurasia. The seasonality in O-3 production over Europe is simulated well, and transport principally in the boundary layer propagates these changes in O-3 over Eurasia, leading to monthly mean impacts at Mondy, Siberia, of 0.5-3.5 ppbv. Impacts over Japan are smaller, 0.2-2.5 ppbv, and are very similar to those from North American sources, which dominate at higher altitudes. By following the effect of daily emissions independently, we clearly demonstrate that this greater North American impact is associated with lifting over the Atlantic. European and North American sources contribute to background O-3 over Japan in the anticyclonic conditions that favor regional O-3 buildup and are thus expected to have a small but significant effect on regional air quality. Finally, we demonstrate that location and transport lead to European sources having a different impact on OH, and hence on tropospheric oxidizing capacity and climate, from other major Northern Hemisphere source regions.