Abstract
Abstract. The long-term temporal–spatial variations in the aerosol optical properties over the Tibetan Plateau (TP) and the potential long-range transport from surrounding areas to the TP were analyzed in this work, by using multiple years of sun photometer measurements (CE318) at five stations in the TP, satellite aerosol products from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), back-trajectory analysis from the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) and model simulations from the Goddard Earth Observing System (GEOS)-Chem chemistry transport model. The results from the ground-based observations showed that the annual aerosol optical depth (AOD) at 440 nm at most TP sites increased in recent decades with trends of 0.001±0.003 yr−1 at Lhasa, 0.013±0.003 yr−1 at Mt_WLG, 0.002±0.002 yr−1 at NAM_CO and 0.000±0.002 yr−1 at QOMS_CAS. The increasing trend was also found for the aerosol extinction Ångström exponent (EAE) at most sites with the exception of the Mt_WLG site. Spatially, the AOD at 550 nm observed from MODIS showed negative trends at the northwest edge close to the Taklimakan Desert and to the east of the Qaidam Basin and slightly positive trends in most of the other areas of the TP. Different aerosol types and sources contributed to a polluted day (with CE318 AOD at 440 nm > 0.4) at the five sites on the TP: dust was the dominant aerosol type in Lhasa, Mt_WLG and Muztagh with sources in the Taklimakan Desert, but fine-aerosol pollution was dominant at NAM_CO and QOMS_CAS with transport from South Asia. A case of aerosol pollution at Lhasa, NAM_CO and QOMS_CAS during 28 April–3 May 2016 revealed that the smoke aerosols from South Asia were lifted up to 10 km and transported to the TP, while the dust from the Taklimakan Desert could climb the north slope of the TP and then be transported to the central TP. The long-range transport of aerosol thereby seriously impacted the aerosol loading over the TP.
Highlights
The heavy haze that has occurred in recent years in China has been largely attributed to the atmospheric aerosols (Zhang et al, 2015)
Based on multiple years of observations from five ground-based sun photometers at the Tibetan Plateau (TP) and the Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth product over the TP region, our work here is focused on the long-term spatiotemporal variations in the aerosol optical properties over the TP and the aerosol properties and sources during the high aerosol loading over the TP
The combined MODIS Dark Target (DT) and Deep Blue (DB) aerosol optical depth (AOD) at 550 nm (MODIS_AOD) merges the products from the two algorithms based on the normalized difference vegetation index (NDVI) statistics as follows: (1) the DT AOD data are used for NDVI > 0.3, (2) the DB AOD data are used for NDVI < 0.2, and (3) the mean of both the algorithms or AOD data with a high-quality flag is used for 0.2 ≤ NDVI ≤ 0.3
Summary
The heavy haze that has occurred in recent years in China has been largely attributed to the atmospheric aerosols (Zhang et al, 2015). Most studies of the aerosol properties based on ground-based measurements have been conducted at a single site over the TP, such as NAM_CO (Cong et al, 2009), Mt_Yulong (Zhang et al, 2012) and Mt_WLG (Che et al, 2011). Based on multiple years of observations from five ground-based sun photometers at the TP and the MODIS aerosol optical depth product over the TP region, our work here is focused on the long-term spatiotemporal variations in the aerosol optical properties over the TP and the aerosol properties and sources during the high aerosol loading over the TP. J. Zhu et al.: Spatiotemporal variation of aerosol and potential long-range transport impact (Tibetan Plateau) 14639. These five sites are representative of the spatial features of the TP
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