Pakpong Pochanart

Influence of regional‐scale anthropogenic activity in northeast Asia on seasonal variations of surface ozone and carbon monoxide observed at Oki, Japan

Surface O3 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 O3 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 O3. The trajectories were categorized into five groups which cover background and regionally polluted air masses. The seasonal cycles of O3 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, O3 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 O3 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 O3 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 O3 from large-scale precursor emissions in both regions is very significant.

Regional background ozone and carbon monoxide variations in remote Siberia/East Asia

[1] Continuous measurements of O3 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 O3 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 O3 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 O3 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 O3 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 O3 and CO at Mondy in remote Siberia/East Asia. INDEX TERMS: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry;

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.

Seasonal variation of carbon monoxide at remote sites in Japan

Abstract Continuous measurement of CO has been carried out at remote sites in Japan, Oki (36°N), Happo (36°N) and Benoki (27°N). Seasonal variation at each site exhibited a clear cycle with a maximum in spring and a minimum in summer. It has been revealed that the concentrations of CO at Oki are substantially higher than at Mace Head throughout a year. Comparison of trajectory-categorized data between Oki and Mace Head has been made to elucidate that the concentration at Oki is higher than Mace Head both in the clean “background” and in the regionally polluted air mass. The spring maximum at Oki occurs in April that is one month later than the reported data at other remote sites in the northern hemisphere.

Diurnal and temporal variations of water-soluble dicarboxylic acids and related compounds in aerosols from the northern vicinity of Beijing: Implication for photochemical aging during atmospheric transport

Aerosol samples were collected in autumn 2007 on day- and nighttime basis in the northern receptor site of Beijing, China. The samples were analyzed for total carbon (TC) and water-soluble dicarboxylic acids (C2-C12), oxocarboxylic acids (C2-C9), glyoxal and methylglyoxal to better understand the photochemical aging of organic aerosols in the vicinity of Beijing. Concentrations of TC are 50% greater in daytime when winds come from Beijing than in nighttime when winds come from the northern forest areas. Most diacids showed higher concentrations in daytime, suggesting that the organics emitted from the urban Beijing and delivered to the northern vicinity in daytime are subjected to photo-oxidation to result in diacids. However, oxalic acid (C2), which is the most abundant diacid followed by C3 or C4, became on average 30% more abundant in nighttime together with azelaic, ω-oxooctanoic and ω-oxononanoic acids, which are specific oxidation products of biogenic unsaturated fatty acids. Methylglyoxal, an oxidation product of isoprene and a precursor of oxalic acid, also became 29% more abundant in nighttime. Based on a positive correlation between C2 and glyoxylic acid (ωC2) in nighttime when relative humidity significantly enhanced, we propose a nighttime aqueous phase production of C2 via the oxidation of ωC2. We found an increase in the contribution of diacids to TC by 3 folds during consecutive clear days. This study demonstrates that diacids and related compounds are largely produced in the northern vicinity of Beijing via photochemical processing of organic precursors emitted from urban center and forest areas.