Ground-based MAX-DOAS observations of tropospheric aerosols, NO<sub>2</sub>, SO<sub>2</sub> and HCHO in Wuxi, China, from 2011 to 2014

Abstract

Abstract. We characterize the temporal variation and vertical distribution of nitrogen dioxide (NO 2 ), sulfur dioxide (SO 2 ), formaldehyde (HCHO) and aerosol extinction based on long-term multi-axis differential optical absorption spectroscopy (MAX-DOAS) observations from May 2011 to November 2014 in Wuxi, China. A new inversion algorithm (PriAM) is implemented to retrieve profiles of the trace gases (TGs) and aerosol extinction (AE) from the UV spectra of scattered sunlight recorded by the MAX-DOAS instrument. We investigated two important aspects of the retrieval process. We found that the systematic seasonal variation of temperature and pressure (which is regularly observed in Wuxi) can lead to a systematic bias of the retrieved aerosol profiles (e.g. up to 20 % for the AOD) if it is not explicitly considered. In this study we take this effect into account for the first time. We also investigated in detail the reason for the differences of tropospheric vertical column densities derived from either the geometric approximation or by the integration of the retrieved profiles, which were reported by earlier studies. We found that these differences are almost entirely caused by the limitations of the geometric approximation (especially for high aerosol loads). The results retrieved from the MAX-DOAS observations are compared with independent techniques not only under cloud-free sky conditions, but also under various cloud scenarios. Under most cloudy conditions (except fog and optically thick clouds), the trace gas results still show good agreements. In contrast, for the aerosol results, only near-surface AE could be still well retrieved under cloudy situations.After applying a quality control procedure, the MAX-DOAS data are used to characterize the seasonal, diurnal and weekly variations of NO 2 , SO 2 , HCHO and aerosols. A regular seasonality of the three trace gases is found, but not for aerosols. Similar annual variations of the profiles of the trace gases appear in different years. Only NO 2 shows a significant seasonality of the diurnal variations. Considerable amplitudes of weekly cycles occur for NO 2 and SO 2 , but not for HCHO and aerosols. The TGs and aerosols show good correlations, especially for HCHO in winter. More pronounced wind direction dependencies, especially for the near-surface concentrations, are found for the trace gases than for the aerosols, which implies that the local emissions from nearby industrial areas (including traffic emissions) dominate the local pollution, while long-distance transport might also considerably contribute to the local aerosol levels.

MAX-DOAS NO<sub>2</sub> observations over Guangzhou, China; ground-based and satellite comparisons

“…A double-peak diurnal cycle has been also reported for other Chinese cities in previous studies, e.g. for Beijing (Ma et al, 2013) and Wuxi (Wang et al, 2017a) levels observed in the Guangzhou area both from space and from the ground. Interestingly, during the overpass days of GOME-10 2B the tropospheric NO2 levels, both in terms of the average value and the standard deviation, are lower relative to GOME-2A and OMI overpass days.…”

“…A double-peak diurnal cycle has been also shown for other Chinese cities, e.g. for Beijing (Ma et al, 2013) and Wuxi (Wang et al, 2017a) in spring and summer.…”

“…The Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) (Platt, 1994;Van Roozendael et al, 2003;Hönninger et al, 2004;Wagner et al, 2004;Wittrock et al, 2004;Platt and Stutz, 2008) is a widely used ground-based remote 10 sensing technique for the retrieval of the vertical column and distribution of various trace gases as well as aerosol properties with relatively high sensitivity in the lower atmosphere (Frieß et al, 2006(Frieß et al, , 2011(Frieß et al, , 2016Clémer et al, 2010;Irie et al, 2008Irie et al, , 2011Wagner et al, 2011). Moreover, MAX-DOAS measurements have been extensively used for the validation of satellite products (e.g.…”

Validation of OMI, GOME-2A and GOME-2B tropospheric NO<sub>2</sub>, SO<sub>2</sub> and HCHO products using MAX-DOAS observations from 2011 to 2014 in Wuxi, China: investigation of the effects of priori profiles and aerosols on the satellite products

“…X. Hendrick et al, 2014;Wang et al, , 2017, a validation of tropospheric satellite products (e.g. Irie et al, 2012Irie et al, , 2016Ma et al, 2013;Kanaya et al, 2014;Theys, et al, 2015;De Smedt et al, 2015;Jin et al, 2016) and an evaluation of chemical transport model (CTM) simulations (e.g.…”

“…Nevertheless, because profile measurements are rare, the SF effect is still not well understood in many regions. In this study the SF effect on the tropospheric AMF will be investigated using the vertical profiles of the TGs derived from the MAX-DOAS observations in Wuxi, China, from 2011 to 2014 (Wang et al, 2017).…”