Investigation of Aerosol Optical Depth (AOD) and Ångström Exponent over the Desert Region of Northwestern China Based on Measurements from the China Aerosol Remote Sensing Network (CARSNET)

Abstract

Aerosols at ten sites in northwestern China are classified in this study: (1) by using the aerosol optical depth (AOD), the Ångström exponent (α) and the Ångström exponent difference (δα); and (2) by using the total means of AOD 440nm and α. The seasonal variations of the AOD and α show that the maximum AODs occur in spring, except at Urumqi and Lanzhou. The seasonal mean α values are lower than 0.80 in all four seasons at Tazhong, Hotan, Hami, Ejina, Dunhuang, Minqin, and Jiuquan, but higher than 0.80 in winter at Urumqi, Lanzhou and Yinchuan. The first classification method shows that coarse mode particles are found at all ten sites, but that fine mode growth only happens at Urumqi, Lanzhou, and Yinchuan. The relationship between AOD 440nm and α show that α smaller than 0.80 decrease with increasing AOD 440nm at all ten sites. Aerosols are classified into four types (Type I-IV) according to the total mean τ 440 ( 440  ) and total mean Ångström exponent ( ) of each site. Aerosols with a τ 440 smaller than 440 , but greater than or equal to  (τ 440 < 440  ; α ≥  ) are classified as Type I; aerosols with τ 440 ≥ 440  and α ≥  are Type II; those with τ 440 < 440  and α <  are Type III; and those with τ 440 ≥ 440  and α <  are Type IV. The second aerosol classification method shows that Type I and Type III aerosols are the most common at all ten sites. Type II aerosols are the least at Tazhong and Hotan, but are the most common at Urumqi, Lanzhou, and Yinchuan. On the contrary, Type IV aerosols are the most common at Tazhong and Hotan, but are the least common at Urumqi, Lanzhou and Yinchuan.

Estimation and inter-comparison of dust aerosols based on MODIS, MISR and AERONET retrievals over Asian desert regions

“…Kumar et al (2014), conducted a comprehensive study on long term (i.e., 2003-2013) trends and variations in aerosol optical depth parameters retrieved from MODIS over three stations of South Africa. Several studies have been published regarding aerosol optical depth and Angstrom exponent in North West China using ground based observations (Kumar et al, 2014;Xiangao et al, 2004;Yu et al, 2015). The Intercomparison of MODIS AOD and MISR AOD against AEROENT AOD have not been conducted yet in Asian dust regions.…”

The optical properties, physical properties and direct radiative forcing of urban columnar aerosols in the Yangtze River Delta, China

“…Bergin et al, 2001;Xu et al, 2002;Zhang et al, 2004Zhang et al, , 2015Xia et al, 2007;Yan et al, 2008;He et al, 2009;Fan et al, 2010;Cai et al, 2011;Xu et al, 2012;Wu et al, 2012;Yu et al, 2016;Deng et al, 2016;Zhuang et al, 2017) and columnar (e.g. Chiang et al, 2007;Pan et al, 2010;Yu et al, 2011Yu et al, , 2015Zhao et al, 2013;Tao et al, 2014;Che et al, 2011Che et al, , 2013Che et al, , 2014Che et al, , 2015aChe et al, , b, c, 2018Xia et al, 2016;Zheng et al, 2016;Qi et al, 2016) aerosol optical properties (and DRFs), especially in China. However, surface data cannot completely represent the total conditions of aerosols in the atmosphere as these aerosols are highly affected by the variations in boundary layers.…”

Spatial distribution and temporal variation of atmospheric pollution in the South Gobi Desert, China, during 2016–2019

“…It is obvious that AOD values may be affected not only by the Badain Jaran Desert, situated east of the city, but also by the Qaidam and the Kumtagh deserts, situated in the west (Wang et al 2017a, b). As compared with other regions, clearly defined overestimated AOD values caused by anthropogenic activity are also revealed in the extreme south and the extreme east, since the region largest cities Lanzhou and Yinchuan are situated here (Yu et al 2015;Zhang 2016;Zheng et al 2018). Generally, it can be noted that the study region does not suffer the extreme aerosol loading as compared with other regions of the country.…”