The lnfluence of Aerosol Particles on Retrieval Accuracy of CO₂Concentration Using Near Infrared Bands

The main difficulty in retrieving CO₂concentration from near-infrared observations comes from the uncertainty of light path change brought about by scattering of the atmospheric aerosols.The scattering effect described by different aerosol models and surface reflectances may lead to different light path changes.This paper aims to study the influence of neglecting aerosol scattering on CO₂retrieval accuracy for different aerosol models.It is found that for rural, tropospheric and marine aerosol models, the neglecting of aerosol scattering results in underestimation of CO₂retrievals at low surface reflectances(< 0.1), but overestimation at surface reflectance over 0.1 and the increasing retrieval errors with increasing surface reflectances.For the urban aerosol model, the neglecting of aerosol scattering results in underestimation of CO₂retrievals at any surface reflection, and the retrieval errors decrease with increasing surface reflectances.For typical observation geometry, a surface reflectance of 0.1-0.3 at 1.6μm and aerosol optical depth(AOD)of 0.1-0.3 at 0.55μm, the neglecting of aerosol scattering leads to retrieval errors of(-0.1%)-(-0.5%), 0.22%-1.92%, 0.09%-1.46% and 0.02%-0.45% for urban, marine, rural and tropospheric aerosol models respectively.XCO₂(the dry air column averaged mixing ratio of CO₂) was retrieved from GOSAT observations with in-situ measurements of aerosol properties as input parameters.Comparison with ground-based XCO₂measurements shows that the retrieved XCO₂(390.95ppm)is more consistent with the measured XCO₂(390.737ppm)as compared to that of GOSAT L2 product(389.814ppm).