Analyses of multiple global and regional aerosol products: investigation of aerosol effects and artifacts

Abstract

Multiple aerosol products derived from satellite, ground-based, and air-borne instruments were analyzed with a focus on satellite-based aerosol products. Aerosol measurements based on different techniques were utilized to investigate the effects and the artifacts of aerosols and clouds by taking advantages of respective techniques. The global aerosol products derived from Advanced Very High Resolution Radiometer (AVHRR) and Total Ozone Mapping Spectrometer (TOMS), were analyzed for extracting synergic information. Global distributions of dominant aerosol type(s) were derived and the two products were combined to acquire an extended spatial coverage of aerosol optical thickness (AOT) at a common wavelength (0.55um). It was shown that the derived AOT agreed reasonably with AOT from the state-of-the-art Moderate Resolution Imaging Spectroradiometer (MODIS). In-depth comparison of aerosol products derived from the MODIS and the AVHRR was performed. New insights and understanding were gained for the discrepancies between the two prominent aerosol products, allowing for bridging the current and past products. Several factors causing the discrepancies were investigated. Cloud-screening techniques and aerosol models employed by the retrieval algorithms were found to be the most important factors explaining the observed discrepancies. The column aerosol humidification effect (AHE) was investigated. The column AHE was shown to be sensitive to changes in relative humidity (RH). Six methods to infer the column AHE were introduced. The knowledge of the AHE helps investigate aerosol properties and retrievals near clouds, enabling separation of aerosol real effects from artifacts associated with clouds. Finally, apparent correlations between AOT and cloud amount from ground- and satellite-based measurements were investigated. Several factors including air convergence, cloud contamination and uncertainty in cloud cover estimation, the AHE, cloud-processed/new particle genesis were studied to explain the correlations. We showed that the correlation found in ground-based measurements is mostly due to real effects while satellite-based measurements are significantly influenced by artifacts caused by clouds.