Aerosol Properties Over Tibetan Plateau From a Decade of AERONET Measurements: Baseline, Types, and Influencing Factors

Abstract

In this study, a decade long measurement of aerosol optical properties at two AERONET stations (Nam Co during 2006–2016 and QOMS during 2009–2017) in the Tibetan Plateau (TP), a region sensitive to climate change and human perturbation, is presented. The baseline value of aerosol optical depth (AOD) was 0.029 and 0.027 at Nam Co and QOMS, respectively, which are comparable to or even lower than those at some Arctic and remote ocean locations. The seasonality of AOD values were the order of spring > summer > winter > autumn. Based on AOD and Ångström exponent (α), major aerosol types over the TP were further identified as continental background, biomass burning, and dust. Although continental background aerosol was the main feature in remote areas of TP, biomass burning plumes frequently occurred, especially during spring (March–April). In one of such biomass burning event in April 2014, MODIS observations demonstrated that intensive open fires occurred in South Asia, covering the foothills of Himalayas and Indo‐Gangetic Plain. The air mass back trajectories and CALIOP observations further revealed that biomass burning plume could be uplifted to higher altitudes and reach the Himalayas. Moreover, an occasional dust event detected in April 2008 over the TP demonstrated that the dust from Taklamakan Desert may impact the main body of TP episodically, although the local dust from the inside of TP cannot be excluded and warrants further study.

Aerosol characteristics at the three poles of the Earth as characterized by Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations

“…Similar patterns of multi-year-averaged seasonal variation in AOD over the three study regions were also observed using the AERONET data, which have high accuracy and are widely used in aerosol characteristics and satellite-based AOD inversion verification studies (Holben et al, 1998;Martonchik et al, 2004;Russell et al, 2010;Yang et al, 2019). Over the TP, the multi-year-averaged AOD reaches a maximum in April and a minimum in December, while the aerosol composition varies greatly at different sites (Cong et al, 2009;Pokharel et al, 2019). High AOD mainly occurs in spring, associated with the Arctic haze, and low AOD occurs in summer over the Arctic (Breider et al, 2014;Grassl and Ritter, 2019;Rahul et al, 2014).…”

“…As an important component, atmospheric aerosols play a crucial role in the Earth-atmosphere system (Garrett and Zhao, 2006;Ghan and Easter, 2006;Nabat et al, 2015;Wei et al, 2021;Xue et al, 2020). Aerosols have a variety of effects on Earth's climate, including the significant direct effect (Rap et al, 2013;Xing et al, 2017), indirect effect (Albrecht, 1989;Liu et al, 2019Liu et al, , 2020aRighi et al, 2011;Twomey, 1977;Zhao and Garrett, 2015) and semi-direct effect (Amiri-Farahani et al, 2017;Johnson, 2005;Koren et al, 2004). Meanwhile, different aerosol types often have different physical, chemical and optical properties, and the balance between cooling and warming depends to some extent on aerosol characteristics (Boucher et al, 2013).…”

“…Although many studies have been carried out on aerosol optical properties over the Arctic, Antarctic and TP, they are mainly based on the short-term ground remote-sensing or in situ observations, which has limited spatial representation (Chaubey et al, 2011;Cong et al, 2009;Eleftheriadis et al, 2004;Engvall et al, 2008;Pokharel et al, 2019) and inadequate information about the vertical distribution of aerosols. Meanwhile, different aerosol types can result in large uncertainty in estimating the aerosol radiative effect (Loeb and Su, 2010).…”

Arctic sea-ice loss intensifies aerosol transport to the Tibetan Plateau

“…Early studies have shown that the annual baseline values of AOD observed at the two stations are nearly equal and very low (0.029 at Nam Co and 0.027 at QOMS) 5 , which reflects the background aerosol loading. In some extreme events in April, the daily AOD at the two stations has a sharp increase by 10−20 times relative to the baseline values ( Supplementary Figs.…”

“…The AOD and Ångström exponent (AE; as a qualitative indicator of aerosol particle size, with low AE indicating coarse particles) can be used together to classify aerosol types into the clean continental background, dust, anthropogenic aerosols (e.g., from biomass burning) or else aerosol mixtures, with a unique criterion over the TP ( Supplementary Fig. 3) 5 . The anthropogenic and dust aerosols are respectively fine and coarse in size 29 .…”