MAX-DOAS measurements of NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;, HCHO and CHOCHO at a rural site in Southern China

X Li,A Wahner,Y P Li,A Hofzumahaus,K Lu,M Shao,T Brauers,T Wagner

doi:10.5194/acp-13-2133-2013

Abstract

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 NOx 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 HOx turnover rate consistent with other observations during the campaign.

Highlights

CMAQ overestimated the NO2 vertical column density (VCD) as well as the surface concentrations by about 65 %
During the PRIDE-PRD2006 campaign in Southern China in July 2006, we performed MAX-DOAS measurements for NO2, HCHO, and CHOCHO at a rural site 60 km NW of downtown Guangzhou
Under the assumption of a “box profile” setup for the three trace gases, their tropospheric vertical column densities, mixing layer heights, and mixing ratios at the ground have been retrieved by an automated algorithm

Summary

Introduction

CMAQ overestimated the NO2 VCDs as well as the surface concentrations by about 65 %. The single scattering assumption is not valid Under these condiaverage mixing ratios of HCHO and CHOCHO were 7 ppb tions, radiative transfer models (RTMs) are required to derive and 0.4 ppb, respectively, higher than in other rural or semiru- trace gas profiles from mHeaysdurreod lSoCgDys. aThneddifferent RTMs ral environments. In order to optimize the model input an inversion meSthcodieisnnceeedsed This can either be optimal estimation (Rodgers, 2000) or an iteration procedure as presented by Pikelnaya et al (2007). Multi-axis differential optical absorption spectroscopy (MAX-DOAS) is an effective remote sensing method for measuring tropospheric trace gases such as SO2, HCHO, NO2, CHOCHO (Irie et al, 2011; Wagner et al, 2011, and references therein). MAX-DOAS uses scattered sunlight at different elevation angles α Given that routine MAX-DOAS measurements often generate large data sets, an automated inversion method (e.g., Irie et al, 2011) is highly preferable

Results

Discussion

Conclusion