Source of surface ozone and reactive nitrogen speciation at Mount Waliguan in western China: New insights from the 2006 summer study

Abstract

[1] Surface ozone (O 3 ), carbon monoxide (CO), and total and speciated reactive nitrogen compounds (NO y , NO, NO 2 , PAN, HNO 3 , and particulate NO 3 − ) were measured at Mount Waliguan (WLG; 36.28°N, 100.90°E, 3816 m above sea level (asl)) in the summer of 2006 to further understand the sources of ozone and reactive nitrogen and to investigate the partitioning of reactive nitrogen over the remote Qinghai-Tibetan Plateau. The mean mixing ratios of O 3 , CO, NO y , and daytime NO were 59 ppbv, 149 ppbv, 1.44 ppbv, and 71 pptv, respectively, which (except for NO y ) were higher than those measured from a previous campaign in summer 2003, which is consistent with more frequent transport of anthropogenic pollution from central and eastern China in the measurement period of 2006 (55%) than that of 2003 (25%). The abnormally high values of NO y observed in 2003 were suspected to be due to the positive interference from ammonia (NH 3 ) to the particular catalytic converter used in that study. Varied diurnal patterns were observed for the various NO y components. The ozone production efficiencies (DO 3 /DNO z ), which were estimated from the slope of the O 3 -NO z scatterplot, were 7.7-11.3 for the polluted plumes from central and eastern China. The speciation of reactive nitrogen was investigated for the first time in the remote free troposphere in western China. PAN and particulate NO 3 − were the most abundant reactive nitrogen species at WLG, with average proportions of 32% and 31%, followed by NO x (24%) and HNO 3 (20%). The relatively large contribution of particulate NO 3 − to NO y was due to the presence of high concentrations of NH 3 and crustal particles, which favor the formation of particulate nitrate. An analysis of backward trajectories for the recent 10 years revealed that air masses from central and eastern China dominated the airflow at WLG in summer, suggesting strong impact of anthropogenic forcing on the surface ozone and other trace constituents on the Plateau.

Mixing state and sources of submicron regional background aerosols in the northern Qinghai–Tibet Plateau and the influence of biomass burning

“…S1, and the PM 2.5 and gaseous concentrations were provided by the NSBAM. The average CO mixing ratio is 44.78 ppb at the NSBAM, much lower than the 149 ppb at Waliguan in the summer of 2006, which is the site of the observation station of the World Meteorological Organization's (WMO) Global Atmospheric Watch (GAW) (Xue et al, 2011). This contrast shows that the NSBAM adequately represents background conditions in the expansive grasslands of the northern TP.…”

“…Table 1 shows that five pollutants' concentrations (i.e., PM 2.5 , BC, SO 2 , NO x , and CO) were higher during these pollution events than in the intervening cleaner period; there was little difference in O 3 concentration among these periods. When the combustiontracing CO and NO x concentrations increase, O 3 mixing ratios generally decrease in the QTP due to photochemical consumption (Xue et al, 2011). The primary BC concentrations during the two pollution events were 17 and 81 % higher than the intervening cleaner period, respectively (Table 1).…”

“…Previous studies have proved that trace gases such as SO 2 , NO x , and volatile organic compounds (VOCs) from anthropogenic and natural sources had been transported over long distances in the QTP and were transformed into secondary aerosol particles (Xue et al, 2011;Du et al, 2015;Xu et al, 2015). For example, Du et al (2015) suggested that oxygenated organic aerosols from anthropogenic sources and biomass burning were transported over a long distance to the sampling site in the QTP.…”

Observations of reactive nitrogen oxide fluxes by eddy covariance above two midlatitude North American mixed hardwood forests

“…Williams et al, 1998), in addition to studies comparing multiple Mo converters with themselves (e.g. Fitz et al, 2003;Xue, et al, 2011). Differences in NO y conversion between the conventional techniques have been reported to be within 5 %, and with an adequate quality control program should not result in significant differences.…”

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

“…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).…”