Rationale. Glaciers in the Tibetan Plateau (TP), especially in the Himalayas, are retreating rapidly due to rising air temperature and increasing anthropogenic emissions from nearby regions. Traditionally, pollutants deposited on the glaciers have been assumed to originate from long-range transport from its outside. Methodology. This study investigated the concentrations of black carbon (BC) and major ions in snowpit samples collected from two glaciers in the south-eastern TP (Demula and Palongzangbu) and one glacier in the west Himalayas (Jiemayangzong). The radiative forcing of BC was calculated based on BC concentration and glacier characteristics. Results. The results revealed that the BC/Ca2+ concentration ratio in snowpit samples from Palongzangbu, located near residential villages, is similar to 2.05 times higher than that of Demula, which is mainly influenced by long-range transported pollutants. Furthermore, on Jiemayangzong glacier, snowpit samples collected with 100-m vertical resolution exhibited that BC-induced radiative forcings at low altitude are similar to 2.37 +/- 0.16 times greater than those at high altitude. Discussion. These findings demonstrated that in addition to long-range transport, emissions from local residents also make substantial contributions to BC and certain major ions (e.g. SO42-). To accurately assess the sources and radiative forcing of BC and other light-absorbing impurities on glaciers of the TP, it is necessary to consider the impact of local populations and altitude-dependent variations.

Understanding the source of atmospheric aerosol is an essential step in determining the aerosol radiative effect over the Tibetan Plateau (TP). This study aims to clarify the contributions of anthropogenic and natural emission to the aerosols (carbonaceous and sulphate) characteristics inside the TP. An aerosol model named Spectral Radiation Transport Model for Aerosol Species (SPRINTARS) recently coupled to the climate model named Chinese Academy of Sciences Flexible Global Ocean Atmosphere Land System (CAS-FGOALS-f3-L) is used to simulate meteorological conditions and aerosols from 1985 to 2013, given emissions from the sixth phase of the Coupled Models Intercomparison Project (CMIP6). Comparisons between the simulations and ERA5 reanalysis data present that the model can capture the key spatial and temporal features of meteorological elements (2-m temperature, relative humidity, and wind field at 500 hPa) over the Asia. Subsequently, we conduct six sensitivity studies to quantify the contributions of sources to aerosol surface concentration, burden and aerosol optical depth (AOD) over the TP. Our results illustrate that the outside and local anthropogenic sources contribute about 75.2% (78.9% in summer and 66.6% in winter) and 13.5% (7.4% in summer and 24.0% in winter) to the annual mean aerosols surface concentrations over the TP. The outside anthropogenic sources contribute to AODs in TP up to 87.3% (93.9% in autumn and 80.6% in winter). The ascending air over the TP is conducive to the transportation of the outsource pollutions to the TP. The outside natural sources (refer to biomass burning sources) contribute about 10% to aerosols over TP, and the inside natural sources play minor roles. The black carbon, organic carbon and sulphate (BOCS) induce average radiative forcing of -0.7 W m(-2) at the near surface over the TP.

This study applies the nested-grid version of Goddard Earth Observing System (GEOS) chemical transport model (GEOS-Chem) to examine future changes (2000-2050) in SOA concentration and associated direct radiative forcing (DRF) over China under the Representative Concentration Pathways (RCPs). The projected changes in SOA concentrations over 2010-2050 generally follow future changes in emissions of toluene and xylene. On an annual mean basis, the largest increase in SOA over eastern China is simulated to be 25.1% in 2020 under RCP2.6, 20.4% in 2020 under RCP4.5, 56.3% in 2050 under RCP6.0, and 44.6% in 2030 under RCP8.5. The role of SOA in PM2.5 increases with each decade in 2010-2050 under RCP2.6, RCP4.5, and RCPS.5, with a maximum ratio of concentration of SOA to that of PM2.5 of 16.3% in 2050 under RCP4.5 as averaged over eastern China (20 degrees-45 degrees N, 100 degrees-125 degrees E). Concentrations of SOA are projected to be able to exceed those of sulfate, ammonium, and black carbon (BC) in the future. The future changes in SOA levels over eastern China are simulated to lead to domain-averaged (20 degrees-45 degrees N, 100 degrees-125 degrees E) DRI's of +0.19 W m(-2), +0.12 W m(-2), -0.28 W m(-2), and -0.17 W m(-2) in 2050 relative to 2000 under RCP2.6, RCP4.5, RCP6.0, and RCP8.5, respectively. Model results indicate that future changes in SOA owing to future changes in anthropogenic precursor emissions are important for future air quality planning and climate mitigation measures. (C) 2018 Elsevier B.V. All rights reserved.