Variation of aerosol optical properties from AERONET observation at Mt. Muztagh Ata, Eastern Pamirs

Abstract

Using data from the ground-based remote sensing Aerosol Robotic Network (AERONET), aerosol optical properties, including aerosol optical depth (AOD), Ångström exponent (α), and volume size distribution were investigated for the period June to December 2011 at Mt. Muztagh Ata (Muztagata), Eastern Pamirs. The monthly average values of AOD (500nm) and α (440–870nm) varied from 0.08±0.02 to 0.16±0.11, and from 0.56±0.06 to 0.93±0.28, respectively. The daily AOD averages 0.14±0.07, with the maximum (0.5) occurring in August and the minimum (0.05) occurring in November. A small increase in AOD is expected with a noticeable decrease in the α value. The daily α averages 0.70±0.27, and most exponents are less than 1, indicating the majority of larger aerosol particles. The volume size distribution of aerosol particles shows bimodal log-normal characteristics, with a fine mode radius of 0.2μm and a coarse mode radius of 3μm. The MODIS AOD and AERONET AOD display a similar variation, while the former is always noticeably higher than the latter with a difference of 0.1–0.4, indicating that the MODIS data might overestimate the aerosol load. Our results indicate that high aerosol volume concentration occurs in summer with the dominance of coarse particles over Muztagh Ata. The low AOD shows a clean atmosphere in this region, revealing that it is an atmospheric background site for continental aerosol monitoring.