On the basis of three mountain sites (Mount Tai, Hua and Huang) newly founded in east‐central China and several other sites from the Acid Deposition Monitoring Network in east Asia (EANET) and WMO World Data Centre for Greenhouse Gases (WDCGG), we investigate seasonal cycle of ozone over east Asia and its budgets in east‐central China by using a regional chemical transport model (NAQPMS). The observations show a striking ozone pattern of two sharp peaks in May‐June and September–October at three mountain sites in east‐central China which are higher than those observed at other mountain sites in Europe and North America. Ozone budgets analysis by the model confirms that maximum of net photochemical productions reaches 31.8, 15.1, and 11.4 ppbv/d at Mount Tai, Hua, and Huang, respectively. The net photochemical production dominates the formation of ozone maximums at Mount Tai and Hua in June, and the importing transport also plays a comparable importance at Mount Huang. In comparison with those in the western North Pacific, east‐central China shows stronger net photochemical productions, which are comparable to anthropogenic sources regions in Europe and North America.

[1] Continuous measurements of O 3 and CO were made during 1997-1999 at Mondy, a remote mountain site in East Siberia, in order to quantify their mixing ratios and their climatology in the ''background'' troposphere of continental Eurasia. The seasonal cycles of O 3 and CO show the spring maximum-summer minimum similar to that previously reported in the remote Northern Hemisphere. The influences of Siberian forest fires on the variations of CO mixing ratios at Mondy were observed both on a local and a regional scale during spring 1997 and fall 1998, respectively. We further evaluate the possible impact of European pollution export to the remote atmosphere of Siberia using trajectory analysis. It was found that the O 3 and CO mixing ratios in the air masses transported from Europe are higher than those from Siberia and high-latitude regions for most of the year. The medians of O 3 and CO mixing ratios associated with the European air masses are 44.2 and 134 ppb, respectively, in comparison with 42.7 and 128 ppb in the Siberian air masses, and 41.0 and 110 ppb in the high-latitude air masses. The residence time analysis of air masses transported from the European continent indicates that CO mixing ratios significantly decrease with longer transport time of air masses from Europe, while rapid air motion retains higher CO mixing ratios in every season due to the admixture of polluted European air into the continental background air during air mass transport over Eurasia and photochemical loss by OH. Because of a shorter lifetime in summer, CO mixing ratios decrease at a rate of 6-7 ppb per day, while they decrease at a rate of 2-4 ppb per day in winter and spring. The similar trend is found for O 3 but only in summer, at a rate of 2-3 ppb per day. From this analysis, we are able to identify that European pollution exerts an influence, though not very strong, on the background O 3 and CO at Mondy in remote Siberia/East Asia.

Abstract. Surface 0 3 and CO measurements were carried out at Oki, Japan during March 1994 to February 1996 in order to elucidate the processes determining temporal variations of 03 and CO in the northeast Asian Pacific rim region. The isentropic trajectory analysis was applied to sort out the influences of the air mass exchange under the Asian monsoon system and the regional-scale photochemical buildup of 03. The trajectories were categorized into five groups which cover background and regionally polluted air masses. The seasonal cycles of 03 and CO in the background continental air mass revealed spring maximum-summer minimum with averaged concentrations ranging from 32 and 120 ppb to 45 and 208 ppb, respectively. In contrast, 03 concentrations in the regionally polluted continental air mass ranged from 44 to 57 ppb and showed a winter minimum and a spring-summer-autumn broad maximum, which was characterized by photochemical 03 production due to anthropogenic activities in northeast Asia. CO concentrations in the same air mass showed a spring maximum of 271 ppb and a summer-autumn minimum of 180 ppb. The photochemical buildup of 03 resulting from anthropogenic activities in this region was estimated to be 21 ppb in summer, while its production was insignificant, an average 3 ppb, in winter. A comparison between data in northeast Asia and in Europe shows many similarities, supporting the contention that photochemical buildup of 03 from large-scale precursor emissions in both regions is very significant.

[1] 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 O 3 from European precursor sources and investigate the extent of their impacts over Eurasia. We focus on measurement sites at 100°E, 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.

Abstract. HO 2 uptake coefficients for ambient aerosol particles, collected on quartz fiber filter using a high-volume air sampler in China, were measured using an aerosol flow tube coupled with a chemical conversion/laser-induced fluorescence technique at 760 Torr and 298 K, with a relative humidity of 75 %. Aerosol particles were regenerated with an atomizer using the water extracts from the aerosol particles. Over 10 samples, the measured HO 2 uptake coefficients for the aerosol particles at the Mt. Tai site were ranged from 0.13 to 0.34, while those at the Mt. Mang site were in the range of 0.09-0.40. These values are generally larger than those previously reported for single-component particles, suggesting that reactions with the minor components such as metal ions and organics in the particle could contribute to the HO 2 uptake. A box model calculation suggested that the heterogeneous loss of HO 2 by ambient particles could significantly affect atmospheric HO x concentrations and chemistry.