Sensitivity of CO2 Retrieval from space to the Shape of Aerosol Particles: a Theoretical Analysis

Aerosols play an important role in the retrieval of trace gases, such as CO2, due to its scattering of solar radiation. Although the impact of the uncertainty of aerosol properties on CO₂ retrieval has been studied, we still have little knowledge about the possible influence from the aerosol particle shapes. The aim of this study is to discuss the impact of the nonspherical dust on CO₂ retrieval from hyperspectral measurements in the space, such as from TanSat and OCO-2. To simulate the CO₂ absorption spectrum with the scattering of randomly oriented polydisperse nonspherical dust particles, a forward model UNL-VRTM (Wang et al., 2014) is further combined by the database of nonspherical dust single-scattering optical properties from Meng et al. (2010). Compared with spherical dust model, the impact of dust nonsphericity on light scattering in CO₂ absorption spectrum is discussed. Furthermore, the dependence of the sensitivity of CO₂ absorption spectrum to dust particle shape on aerosol properties and observation geometries are also analyzed. It is found that the larger difference of dust scattering phase matrix between spherical and nonspherical model near backscattering directions cause the larger sensitivity of CO₂ spectrum at these viewing angles. The uncertainties of aerosol properties from imperfect particle shape description are more important for CO₂ retrieval for larger aerosol optical depths (AOD). This study makes an essential foundation for the reduction of the interference from nonspherical aerosols in CO₂ retrieval and the improvement of CO₂ retrieval precision in the future.