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- Title
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.
- Authors
Wang, Y.; Lampel, J.; Xie, P.; Beirle, S.; Li, A.; Wu, D.; Wagner, T.
- Abstract
We characterize the temporal variation and spatial distribution of nitrogen dioxide (NO2), sulphur dioxide (SO2), formaldehyde (HCHO) and aerosol extinctions using vertical profiles derived from 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 20% for the AOD) if it is not explicitly considered. In this study we take this effect for the first time into account. We also investigated in detail the reason for the differences of tropospheric VCDs 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 agreement. In contrast, from the aerosol results only near-surface AEs could be still well retrieved under cloudy situations. After a quality controlling procedure, the MAX-DOAS data are used to characterize the seasonal, diurnal, and weekly variations of NO2, SO2, HCHO and aerosols. A regular seasonality of the three trace gases is found, but not for aerosols. Similar diurnal variations are found for SO2, HCHO and aerosols in different seasons, but not for NO2. Similar annual variations of the profiles are found in different years, especially for the trace gases. Considerable amplitudes of weekly cycles occur for NO2 and SO2, but not for HCHO and aerosols. Good correlations between the TGs and aerosols are found, especially for HCHO in winter. Significant wind direction dependencies of the trace gases, especially for the near-surface concentrations, are found, but only a weak dependence is found for aerosol properties, especially the AOD. Our findings imply that the local emissions from the industrial area (including traffic emissions) dominate the amount of local pollutants while long distance transport might also considerably contribute to the local aerosol levels.
- Subjects
WUXI (Jiangsu Sheng, China); TROPOSPHERIC aerosols; FORMALDEHYDE &; the environment; SULFUR dioxide &; the environment; NITRIC oxide &; the environment; SEASONAL temperature variations
- Publication
Atmospheric Chemistry & Physics Discussions, 2016, p1
- ISSN
1680-7367
- Publication type
Article
- DOI
10.5194/acp-2016-282