Ambient concentrations of aldehydes in relation to Beijing Olympic air pollution control measures

Abstract

Aldehydes are ubiquitous constituents of the atmosphere. Their concentrations are elevated in polluted urban atmospheres. The present study was carried out to characterize three aldehydes of most health concern (formaldehyde, acetaldehyde, and acrolein) in a central Beijing site in the summer and early fall of 2008 (from June to October). Measurements were made before, during, and after the Beijing Olympics to examine whether the air pollution control measures implemented to improve Beijing's air quality during the Olympics had any impact on concentrations of the three aldehydes. Average concentrations of formaldehyde, acetaldehyde and acrolein were 29.34 ± 15.12 μg/m<sup>3</sup>, 27.09 ± 15.74 μg/m<sup>3</sup> and 2.32 ± 0.95 μg/m<sup>3</sup>, respectively, for the entire period of measurements, all being the highest among the levels measured in cities around the world in photochemical smog seasons. Among the three measured aldehydes, only acetaldehyde had a substantially reduced mean concentration during the Olympic air pollution control period compared to the pre-Olympic period. Formaldehyde and acrolein followed the changing pattern of temperature and were each significantly correlated with ozone (a secondary product of photochemical reactions). In contrast, acetaldehyde was significantly correlated with several pollutants emitted mainly from local emission sources (e.g., NO<sub>2</sub>, CO, and PM<sub>2.5</sub>). These findings suggest that local direct emissions had a larger impact on acetaldehyde than formaldehyde and acrolein

Missing OH source in a suburban environment near Beijing: observed and modelled OH and HO<sub>2</sub> concentrations in summer 2006

“…M0 applies no constraints, whereas the other runs (HCHO×2, HCHO/2, OVOC/2) are constrained to half or twice the HCHO/OVOC concentrations calculated by M0. of a variation of HCHO only, the daytime averaged concentrations are about 6 ppb and 24 ppb, respectively, well situated at the lower and upper bounds of the previously reported HCHO concentration range (5-25 ppb) in Beijing Gong et al, 2010). For these boundary conditions, the modelled OH concentrations prove to be rather insensitive and remain constant within 10 % (Fig.…”

“…The modelled (M0) concentration of HCHO, one of the major calculated OVOCs, is on average 10-15 ppb at daytime. These values are well situated in the range (5-25 ppb) characterized by other groundbased measurements performed in summer at Beijing Gong et al, 2010). At our site, boundary-layer averaged HCHO concentrations of about 6 ppb were determined remotely by multi-axis differential optical absorption spectroscopy (MaxDOAS) for a few days (18,19,21,27,29,31 August) .…”

“…At our site, boundary-layer averaged HCHO concentrations of about 6 ppb were determined remotely by multi-axis differential optical absorption spectroscopy (MaxDOAS) for a few days (18,19,21,27,29,31 August) . Compared to the reported HCHO measurements Gong et al, 2010), the modelled (M0) concentrations of HCHO appear reasonable for this region and time of the year.…”

“…Other field studies which investigated the OH chemistry in urban environments during summertime, took place in Los Angeles (George et al, 1999), Nashville , New York , Tokyo (Kanaya et al, 2007), London (Emmerson et al, 2007), Mexcio City (Shirley et al, 2006;Sheehy et al, 2010;Dusanter et al, 2009) and Houston . A common feature of these cities are large VOC reactivities (10-200 s −1 ) and generally high NO concentrations (1-70 ppb).…”

“…For some cities, the models overpredict the summertime OH observations. For example, an overprediction by a factor of 1.24 and up to 1.5 was found in London (Emmerson et al, 2007) and Los Angeles (George et al, 1999), respectively. In the other cities, underpredictions by up to a factor of two were reported (cf.…”