Simultaneous retrieval of aerosol optical properties over the Pearl River Delta, China using multi-angular, multi-spectral, and polarized measurements

The optical properties of aerosol have been simultaneously retrieved over the Pearl River Delta (PRD), China during December 2009 from multi-angular, multi-spectral, and polarized airborne data. A new airborne Directional Polarimetric Camera (DPC) with high spatial resolution (4 m at 4000 m a.g.l.) is used to retrieve the aerosol optical properties, which is an experimental airborne instrument focused on monitoring aerosol particle pollution, dealing with the apportionment of sources and controlling air quality in cities. We present a case study of polarized observations performed during high air pollution episodes in the southeast of China. Exceptionally high values of the aerosol optical depth of up to 0.8 (at 0.865 μm) were observed in this case study. The spatial and temporal variability of aerosol optical properties over the Pearl River Delta region were analyzed using polarized measurements with high spatial resolution. To reduce the ambiguity in retrieving aerosol optical properties using DPC alone, ground-based measurements (Automatic CE318-DP polarized sun-sky radiometer, Raman Lidar) were used to constrain the inversion in terms of the key characteristics of a local aerosol model, including spectral complex refractive index, size distribution, and vertical distribution of aerosol optical parameters. The surface contribution to the polarized radiance was simulated using bidirectional polarized reflectance distribution function (BPDF), which was adjusted using DPC measurements at low altitude. The aerosol optical properties were retrieved using DPC over the Pearl River Delta, and are in good agreement with coincident sun photometer retrievals. The retrieval algorithm of aerosol optical properties using high spatial resolution polarized measurements proposed in this paper shows potential to retrieve the aerosol optical properties over cities.

Research highlights
► Algorithm for simultaneously retrieving aerosol optical depth and Ångstrom exponent was developed.
► New directional and polarized instrument with high spatial resolution was developed.
► The new instrument is useful for retrieving aerosol properties over cities.
► Spatial and temporal variability of aerosol properties over PRD region were analyzed.