On the origin of surface ozone and reactive nitrogen observed at a remote mountain site in the northeastern Qinghai‐Tibetan Plateau, western China

Abstract

[1] Measurements of surface ozone (O 3 ), carbon monoxide (CO), nitric oxide (NO), and total reactive nitrogen (NO y ) were made, in conjunction with other trace gases and fine aerosols, at Mount Waliguan (WLG, 36.28°N, 100.90°E, 3816 m above sea level) in the late spring and summer of 2003 in order to better understand the source(s) of ozone and other chemically active gases over the remote highlands of western China. The average mixing ratio (plus or minus standard deviation) was 58 (±9) ppbv for O 3 , 155 (±41) ppbv for CO, and 3.83 (±1.46) ppbv for NO y in the spring phase, compared to a summer average value of 54 (±11) ppbv for O 3 , 125 (±36) ppbv for CO, and 3.60 (±1.13) ppbv for NO y . The daytime (0800-1759 local time) average NO mixing ratios were 72 (±79) pptv and 47 (±32) pptv in the spring and summer, respectively. The ozone mixing ratios exhibited a minimum in late morning, while CO (and NO y in spring) showed enhanced concentrations at night. The latter is in contrast to the diurnal behaviors observed in many remote mountain sites. Analysis of 10-day back trajectories using output from FifthGeneration National Center for Atmospheric Research/Penn State University Mesoscale Model (MM5) simulations shows that air masses from the remote western regions contained the lowest level of CO (121-129 ppbv) but had the highest O 3 (60 ppbv), compared to the other three air mass groups that were impacted by anthropogenic emissions in eastern/southern China and in the Indian subcontinent. Ozone correlated negatively with CO (and water vapor content), particularly during summer in air originating in the west, suggesting that the high-ozone events were mostly derived from the downward transport of the upper tropospheric air and not from anthropogenic pollution. An examination of in situ chemical measurements (CO-NO y correlation, ethyne/ propane, and benzene/propane) as well as Measurements of Pollution in the Troposphere (MOPITT) and Moderate-Resolution Imaging Spectroradiometer (MODIS) remotesensing data revealed some impacts from forest fires in central Asia in the late spring of 2003 on the background concentrations of trace gases over western China. While the O 3 and CO levels at WLG are comparable to those at remote continental sites in Europe and North America, the NO y concentrations were substantially higher at WLG. The possible reasons for the abnormally high NO y levels are discussed. While more studies are needed to pin down these sources/causes, including a possible contribution from long-range transport, we believe that microbial processes in soils and animal wastes associated with animal grazing were an important cause of the elevated NO y . The observed daytime NO concentrations imply a net photochemical production of O 3 at WLG, suggesting a positive contribution of photochemistry to the ozone budget.

Impacts of the East Asian summer monsoon on interannual variations of summertime surface-layer ozone concentrations over China

“…Our simulated surface-layer concentrations of O 3 are high in both western and eastern China, which agree with the modeling studies of Wang et al (2011), Jeong andPark (2013), and Lou et al (2014). The high O 3 concentrations in western China are associated with the downward transport of O 3 from the stratosphere to troposphere (Wild and Akimoto, 2001;T. Wang et al 2006a;Ding and Wang, 2006), and the high O 3 concentrations in eastern China result from anthropogenic emissions (Wang et al, 2011).…”

Ozone concentrations, flux and potential effect on yield during wheat growth in the Northwest-Shandong Plain of China

“…For example, the maximum value at the Waliguan site in the Qinghai-Tibet Plateau (3810 m asl) took place at night or early morning, and there was little diurnal variation. This is caused by the extremely low levels of O 3 precursors in the closed natural background condition (Ma et al, 2002;Wang et al, 2006). The difference in O 3 concentration during the day and night showed that O 3 was produced by local photochemical reactions at this site (Crutzen et al, 1999;Xu et al, 2008).…”

Long-term trends of surface ozone and its influencing factors at the Mt Waliguan GAW station, China – Part 1: Overall trends and characteristics

“…Surface ozone at the site has been proved to be highly representative of free-tropospheric ozone (Ma et al, 2002b) and hence is subjected to the influences of STE events (Ding and Wang, 2006;Zhu et al, 2004). Air masses from the west are dominant at WLG and were found to be associated with the highest ozone mixing ratios (Wang et al, 2006b). Only in summer a substantial portion of the airflows comes from the eastern sector and exposes the surface ozone mixing ratio to some regional anthropogenic influences (Wang et al, 2006b;Xue et al, 2011).…”

“…Air masses from the west are dominant at WLG and were found to be associated with the highest ozone mixing ratios (Wang et al, 2006b). Only in summer a substantial portion of the airflows comes from the eastern sector and exposes the surface ozone mixing ratio to some regional anthropogenic influences (Wang et al, 2006b;Xue et al, 2011). Previous studies of ozone at WLG, based on short-term measurements and modelling results, clarified the causes for certain episodes or for the diurnal and seasonal cycles of ozone (Ma et al, 2002a(Ma et al, , 2005Zhu et al, 2004).…”