Five Years of Ground-Based MAX-DOAS Observations of CHOCHO and HCHO in the Beijing Area

Abstract:

Glyoxal (CHOCHO) and formaldehyde (HCHO) are among the most important carbonyl compounds in the atmosphere. Given their short lifetime (typically a few hours) and since they are mainly produced by the oxidation of biogenic and anthropogenic volatile organic compounds (VOCs), they are very good proxy for detecting active VOCs chemistry which can be responsible for the formation of pollutants such as tropospheric ozone and secondary organic aerosols. Both CHOCHO and HCHO are also directly released by biomass burning and fossil fuel combustion. Measuring these species is therefore of major importance for air quality monitoring, especially given the scarcity of available observational data sets.

In this presentation, CHOCHO and HCHO vertical profiles and corresponding column densities are retrieved from ground-based MAX-DOAS (Multi-AXis Differential Optical Absorption Spectroscopy) measurements in the Beijing city center and at the suburban site of Xianghe located at 60km East of Beijing. The periods covered by the observations are June 2008-April 2009 in Beijing and March 2010-December 2014 in Xianghe. We first investigate the capability of the MAX-DOAS technique to measure these species in such highly-polluted environment. Then the diurnal and seasonal cycles of CHOCHO and HCHO near-surface concentrations and vertical column densities as well as the corresponding CHOCHO/HCHO ratios (R_GF) are examined on a long-term basis at both locations. This R_GF ratio is often used as an indicator of changes in the atmospheric VOC mixture. Finally, these diurnal and seasonal cycles are further assessed using simulations from the 3D chemistry transport model IMAGES and observations from the OMI and GOME-2 satellite nadir sensors.