Retrieval and validation of aerosol and NO2 profiles over Nanjing using Mini-MAX-DOAS instrument

Kurzfassung

Air pollution is one of the most important environmental problems in developing Asian countries like China. Nanjing (32.06o N, 118.80o E) is a megacity with a large population and a developed economy in eastern China. In this region, knowledge gaps still exist in the understanding of the source and transport of air pollutants because only few measurement studies have been conducted. From April 2013, A miniature Multi-Axis - Differential Optical Absorption Spectroscopy (Mini-MAX-DOAS) instrument was installed in the Station for Observing Regional Processes of the Earth System (SOPRES) in Nanjing. One-year measurements from June 2013 till May 2014 are applied in this study. These measurements enable the retrieval of aerosol and trace gas profiles like Nitrogen dioxide (NO2). Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) is a novel technique to measure key trace gas species and aerosols simultaneously. The MAX-DOAS instrument is based on optical Ultraviolet (UV) – Visible (VIS) spectrometer that observes scattered sunlight from multiple viewing directions. By combining the zenith sky and different viewing directions, Differential Slant Column Densities (DSCDs) are acquired from the record spectra (F. Hendrick et al., 2014; U. Platt,J. Stutz, 2008). Then the vertical profiles can be retrieved by means of bePRO inversion algorithm (K. Clémer et al., 2010) on these DSCDs. The retrieval results include total Aerosol Optical Depths (AODs), aerosol extinction vertical profiles, NO2 total Vertical Column Densities (VCDs), and NO2 near surface(0 ~ 200 m layer) Volume Mixing Ratios (VMRs). Their seasonal and diurnal variations are invested. A good correlation (0.5491 ~ 0.9972) is obtained.