Absorption Angstrom Exponent of Dust Aerosols Over the Tarim Basin

Abstract

The first ever (to our knowledge) long-term characteristics of aerosol absorption optical depth (AAOD) and then absorption Angstrom exponent (AAE) over the Tarim Basin during 2005-2018 are investigated based on the latest Ozone Monitoring Instrument (OMI) retrievals. This paper aims at evaluating the AAOD and AAE in terms of annual, seasonal, and monthly variations, and referential AAE values of dust aerosols over the Tarim Basin. Our results reveal that the AAOD increases by a factor of nearly 2 from 2015 to 2018, with yearly average values from 0.08 to 0.14 and from 0.04 to 0.07 at 388 and 500 nm, respectively, indicating that the situation of dust aerosol pollution in the Tarim Basin has become severe in recent years. The AAE based on the AAODs at wavelengths of 388 and 500 nm over the Tarim Basin exhibits large variations, with a range of 2.5-3.8. The seasonality of AAOD depicts maximum levels in spring, moderate levels in winter and autumn, and minimum levels in summer, whereas the AAE shows a distinctive pattern with high values in summer and low levels in winter. The monthly mean AAOD values vary by twofold, while monthly average AAE is in a range of 2.8-3.3, with the lowest value in February and the highest in June. The daily AAE between 388 and 500 nm for dust episodes is found to be in a range of 3.2-3.6, with a mean of 3.3, which hopefully provides typical AAE values of dust aerosols over the Tarim Basin.