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

Abstract

High frequency measurements of carbon monoxide (CO) recorded over three years at Mount Waliguan (WLG), a global background station in remote western China, were examined using back trajectory analysis. Corrections for the drift in reference gases were also included in the data revision. Between July 2004 and June 2007, a time series of 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 have been 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 effected by short-term enhancements that exceeded background levels two or more times. The CO data were compared to the values observed at the high alpine research station 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 much greater at the site in China. The air parcels arriving at WLG came predominately from the West, except in summer when advection from the East and Southeast prevailed. Transport from the East 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 large sources of CO. These background conditions were observed most frequently when air masses originated 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

Atmospheric observations of carbon monoxide and fossil fuel CO2emissions from East Asia

“…The background value for a given sampling time and trace gas species is obtained by interpolating in both space and time from a global marine boundary layer map [ Masarie and Tans , 1995]. We considered alternative background choices, such as measurements from sites upwind of TAP at Mt Waliguan, China (WLG, 36.29°N, 100.90°E, 3,810 masl) [ Zhang et al , 2011], or Ulaan Uul, Mongolia (UUM, 44.45°N, 111.10°E, 914 masl) for this purpose, but in both cases, these sites sometimes exhibit mole fractions higher than those at TAP, suggesting occasional local influences, and/or that these sites are not always upwind of the TAP site. High altitude clean air sites such as Mauna Loa, Hawaii (MLO, 19.54°N, 155.58°W, 3,402 masl) or Niwot Ridge, Colorado (NWR, 40.05°N, 105.58°W, 3,526 masl) are also possible choices, but we find that these sites do not adequately characterize the seasonal cycles at the surface, particularly for CO.…”

Background variations of atmospheric CO2 and carbon‐stable isotopes at Waliguan and Shangdianzi stations in China

“…Pollution‐classified mole fractions (red dots) exhibit larger fluctuations than the background measurements. The fluctuations can be attributed to the large‐scale emission and transport from the Yellow River Canyon industrial area in the northeastern region approximately 500 km away from WLG [ Tang et al ., ; Zhang et al ., ]. At the same time, the data at SDZ show larger episodic events influenced by air masses from Beijing and other industrialized areas in the North China Plains [ Lin et al ., ; Zhang et al ., ].…”