MAX-DOAS measurements of NO₂, HCHO and CHOCHO at a rural site in Southern China

Abstract. We performed MAX-DOAS measurements during the PRIDE-PRD2006 campaign in the Pearl River Delta region (PRD), China, for 4 weeks in July 2006 at a site located 60 km north of Guangzhou. The vertical distributions of NO₂, HCHO, and CHOCHO were independently retrieved by an automated iteration method. The NO₂ mixing ratios measured by MAX-DOAS showed reasonable agreement with the simultaneous, ground based in-situ data. The tropospheric NO₂ vertical column densities (VCDs) observed by OMI on board EOS-Aura satellite were higher than with those by MAX-DOAS. The 3-D chemical transport model CMAQ overestimated the NO₂ VCDs as well as the surface concentrations by about 65%. From this observation, a reduction of NO_x emission strength in CMAQ seems to be necessary in order to well reproduce the NO₂ observations. The average mixing ratios of HCHO and CHOCHO were 7 ppb and 0.4 ppb, respectively, higher than in other rural or semirural environments. The high ratio of 0.062 between CHOCHO and HCHO corresponds to the high VOCs reactivity and high HO_x turnover rate consistent with other observations during the campaign.