Aerosol mixtures, which are still unclear in current knowledge, may cause large uncertainties in aerosol climate effect assessments. To better understand this research gap, a well-developed online coupled regional climate-chemistry model is employed here to investigate the influences of different aerosol mixing states on the direct interactions between aerosols and the East Asian summer monsoon (EASM). The results show that anthropogenic aerosols have high-level loadings with heterogeneous spatial distributions in East Asia. Black carbon aerosol loading accounts for more than 13% of the totals in this region in summer. Thus, different aerosol mixing states cause very different aerosol single scattering albedos, with a variation of 0.27 in East Asia in summer. Consequently, the sign of the aerosol instantaneous direct radiative forcing at the top of the atmosphere is changed, varying from - 0.95 to + 1.50 W/m(2) with increasing internal mixing aerosols. The influence of aerosol mixtures on regional climate responses seems to be weaker. The EASM circulation can be enhanced due to the warming effect of anthropogenic aerosols in the lower atmosphere, which further induces considerable aerosol accumulation associated with dynamic field anomaly, decrease in rainfall and so on, despite aerosol mixtures. However, this interaction between aerosols and the EASM will become more obvious if the aerosols are more mixed internally. Additionally, the differences in aerosol-induced EASM anomalies during the strongest and weakest monsoon index years are highly determined by the aerosol mixing states. The results here may further help us better address the environmental and climate change issues in East Asia.

To establish the direct climatic and environmental effect of anthropogenic aerosols in East Asia in winter under external, internal, and partial internal mixing (EM, IM and PIM) states, a well-developed regional climate-chemical model RegCCMS is used by carrying out sensitive numerical simulations. Different aerosol mixing states yield different aerosol optical and radiative properties. The regional averaged EM aerosol single scattering albedo is approximately 1.4 times that of IM. The average aerosol effective radiative forcing in the atmosphere ranges from -0.35 to +1.40 W/m(2) with increasing internal mixed aerosols. Due to the absorption of black carbon aerosol, lower air temperatures are increased, which likely weakens the EAWM circulations and makes the atmospheric boundary more stable. Consequently, substantial accumulations of aerosols further appear in most regions of China. This type of interaction will be intensified when more aerosols are internally mixed. Overall, the aerosol mixing states may be important for regional air pollution and climate change assessments. The different aerosol mixing states in East Asia in winter will result in a variation from 0.04 to 0.11 K for the averaged lower air temperature anomaly and from approximately 0.45 to 2.98 mu g/m(3) for the aerosol loading anomaly, respectively, due to the different mixing aerosols.

The refractive index of ambient aerosols is one of the most important parameters indicating the scattering and absorption properties of aerosols. We proposed a new method for retrieving the refractive index (RI) of ambient particles. The main advantage of our method is that it assimilates the single particle mixing states measured by a single-particle soot photometer, when compared to the traditional optical method of retrieving the ambient aerosol RI. This method was validated by good consistency between the determined RI with this method and retrieved RI with the method of Zhao et al. (2019c) using datasets from field measurements conducted in East China in June of 2018. The results show that the real part of the refractive index of the black carbon (BC)-free particles ranged between 1.37 and 1.51 and this value changed little across different tested wavelengths. The mean complex refractive index for the refractory BC was 1.67 +/- 0.67i at 525 nm. The mean imaginary parts of the other non-BC components were 0.019 and 0.023 at 450 nm and 370 nm respectively. Brown carbon contributed to 5%, 13% and 29% of the ambient aerosol light absorption at 525 nm, 450 nm and 370 nm respectively in East China. This study provides the ability to determine the ambient aerosol complex refractive index and these data can be used in models to reduce the uncertainties in estimating aerosol radiative forcing.

Pollutants, which are usually transported from urban cities to remote glacier basins, and aerosol impurities affect the earth's temperature and climate by altering the radiative properties of the atmosphere. This work focused on the physicochemical properties of atmospheric pollutants across the urban and remote background sites in northwest China. Information on individual particles was obtained using transmission electron microscopy (TEM) and energy dispersive X-ray spectrometry (EDX). Particle size and age-dependent mixing structures of individual particles in clean and polluted air were investigated. Aerosols were classified into eight components: mineral dust, black carbon (soot)/fly ash, sulfates, nitrates, NaCI salt, ammonium, organic matter, and metals. Marked spatial and seasonal changes in individual particle components were observed in the study area. Aerosol particles were generally found to be in the mixing state. For example, salt-coated particles in summer accounted for 31.2-44.8% of the total particles in urban sites and 37.5-74.5% of the total particles in background sites, while in winter, almost all urban sites comprised >50%, which implies a significant effect on the radiative forcing in the study area. We found that in PM2.5 section, the internally mixed black carbon/organic matter particles clearly increased with diameter. Moreover, urban cities were characterized by atmospheric particles sourced from anthropogenic activities, whereas background locations exhibited much lower aerosol concentrations and increased particle density, originating from natural crustal sources (e.g., mineral dust and NaCI salt), which, together with air mass trajectory analysis, indicates a potential spatial transport process and routes of atmospheric transport from urban cities to background locations. Thus, this work is of importance in evaluating atmospheric conditions in northwest China and northeast Tibetan Plateau regions, to discover the transport processes and facilitate improvements in climatic patterns concerning atmospheric impurities. (C) 2018 Elsevier Ltd. All rights reserved.

An online coupled regional climate and chemistry model was used to investigate the direct effects of anthropogenic aerosols (sulfate, nitrate, black carbon BC and organic carbon OC) with different mixing states over China. Three mixing assumptions were considered, including external (EM), internal (IM, BC-core surrounded by well mixed scattering-shells) and partially internal (PIM, 32.2% of sulfate and nitrate, 35.5% of BC and 48.5% of OC were internally mixed) mixtures. Results indicated that high levels of anthropogenic aerosols were found in Southwest and Central to East China. Regional mean surface loadings of sulfate, nitrate, BC, primary OC over China were 9.56, 3.64, 2.30, and 2.99 mu g m(-3), respectively. PIM-aerosol optical depth and single scattering albedo, which were consistent with AERONET and satellite observations, were 0.51 +/- 0.37 and 0.95 +/- 0.02 in Central to East China, implying that proportions of internally mixed aerosols in PIM were reasonable to some degrees. Both aerosol direct radiative forcing (DRF) and corresponding climate responses were sensitive to aerosol mixing states and BC/OC hygroscopicities. The more BC was internally mixed or hydrophilic, the more solar radiation was absorbed, thus leading to more decreases in cloud amount (CA) and subsequently less surface cooling. Combining with the uncertainties of BC/OC hygroscopicities, regional mean PIM-aerosol DRF at the top of atmosphere ranged from -0.78 to -0.61 W m(-2) in all-sky and from -5.24 to -4.95 W m(-2) in clear-sky. Additionally, responses of cloud amount and water path, total column absorbed solar radiation (TCASR), surface air temperature and precipitation (TP) to PIM-aerosol DRFs over China were about -0.45 similar to -0.37%, -0.44 similar to -0.32 g m(-2), +0.69 similar to +0.72 W m(-2), -0.13 similar to -0.11 K and -4.56 similar to -4.29%, respectively. These responses were also sensitive to the lateral boundary condition perturbations especially for CA, TCASR and TP, while DRFs themselves were not. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.