Evaluation of in situ measurements of atmospheric carbon monoxide at Mount Waliguan, China

Abstract

Abstract.Quasicontinuous measurements of carbon monoxide (CO) recorded over three years at Mount Waliguan (WLG), a global baseline station in remote western China, were examined using back trajectory analysis. The data include a revision to correct the working reference scale to the WMO2000 scale and corrections for drift in the reference gases. Between July 2004 and June 2007, CO exhibited large fluctuations and the 5 %, 50 % and 95 %-percentiles of relevant CO mixing ratios were 102 ppb, 126 ppb and 194 ppb. Approximately 50 % of all observed data were selected as CO background data using a mathematical procedure of robust local regression, with the remainder affected by regional-scale pollution. The monthly mean background CO mixing ratios showed a minimum in summer and a maximum in late winter, although all seasons were affected by short-term enhancements that exceeded background levels. The CO data were compared to values observed at the high alpine research station at Jungfraujoch, Switzerland. Smaller seasonal amplitudes were observed at WLG compared to the Jungfraujoch due to lower winter and spring CO levels, however, episodic enhancements of polluted air were greater at WLG. The air parcels arriving at WLG came predominately from the west, except in summer when advection Correspondence to: L. X. Zhou (zhoulx@cams.cma.gov.cn) from the east and southeast prevailed. Transport from the east or southeast typically brought polluted air to the site, having passed over populated urban areas upwind. A large number of elevated CO mixing ratios could also be associated with advection from the northwest of WLG via the central Xinjiang Uygur Autonomous Region (XUAR) and the Ge'ermu urban area where growing industrial activities as well as crops residue burning provide sources of CO. Air masses passing over northwestern Gansu were associated with relatively high CO values suggesting an anthropogenic influence, which was likely due to anthropogenic emissions from northwestern China (based on back-trajectory and potential source contribution analysis and on the INTEX-B: intercontinental Chemical Transport Experiment-Phase B). Background conditions were observed most frequently in air parcels from remote Tibet west of WLG. The probability that air parcels pass over regions of clean or polluted regions was further identified using potential source contribution function (PSCF) analysis.

Implications for CO₂ emissions and sinks changes in western China during 1995–2008 from atmospheric CO₂ at Waliguan

“…Surprisingly, we find that potential source regions of CO 2 are extensively distributed west of the site (Zhang et al, 2011), which was unexpected since the area is typically regarded as relatively remote and clean. High CO 2 concentrations in the area have also been retrieved based on the satellite data (Bai et al, 2010), which further indicates strong CO 2 sources.…”

“…Overall, DCO 2 (W_E) increases much more dramatically in winter than in summer. According to our previous studies (Zhou et al, 2003;Zhang et al, 2011), CO 2 spikes in winter were closely associated with dominant air parcels especially from the northwestern regions of the site, such as the Taklimakan Desert and Tarim Basin, both of which have been largely developed in past decades due to a wealth of oil and gas resources. In summer, these spikes frequently occur due to prevailing air masses originating from northeastern or eastern regions (e.g.…”

“…They were observed with some episodes (red dots) distributed above the background levels (black dots). Back-trajectories for the specific periods of high CO 2 have correlated these polluted episodes to regions with large emission sources (Zhang et al, 2011) that are especially active in the winter/early spring season. CO 2 with relatively low values correspond to sequestrations primarily due to enhanced photosynthetic effects (green dots).…”

General overview: European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) – integrating aerosol research from nano to global scales

“…We carefully selected the observation sites in these four countries to be representative for the regional atmospheric aerosol. This activity completes efforts of EU scientists to develop and sustain monitoring activities of short-lived species in developing and emerging countries (see for example Zhang et al, 2011;Henne et al, 2008;Bonasoni et al, 2008Bonasoni et al, , 2010. In this section, we highlight findings from the EUCAARI measurements in these four countries.…”

Long-term measurements of aerosol and carbon monoxide at the ZOTTO tall tower to characterize polluted and pristine air in the Siberian taiga

“…To define CO mixing ratios representing background air (or the other way around to define the polluted periods) we made use of a non-parametric statistical approach named REBS (robust extraction of background signal). This technique has been previously applied for the identification of background CO concentrations for long-term measurements at the highalpine background site at Jungfraujoch (Ruckstuhl et al, 2012) and at a global background station in China (Zhang et al, 2011a). In our application, we use a bandwidth of three months following the suggestion of Ruckstuhl et al (2012).…”