In-situ measurements of aerosol optical properties were conducted at Mt. Huang from September 23 to October 28, 2012. Low averages of 82.2, 10.9, and 14.1 Mm(-1) for scattering coefficient (sigma(sp), (neph), (550)), hemispheric backscattering coefficient (sigma(hbsp,) (neph), (550)), and absorption coefficient (sigma(ap), (550)), respectively, were obtained. Atmospheric aging process resulted in the increase of sigma(ap), (550) but the decrease of the single scattering albedo (omega(550)) at constant aerosol concentration. However, the proportion of non-light-absorbing components (non-BCs) was getting higher during the aging process, resulting in the increase of aerosol diameter, which also contributed to relatively higher sigma(sp), (neph), (550) and omega(550). Diurnal cycles of sigma(sp), (neph), (550) and sigma(ap), (550) with high values in the morning and low values in the afternoon were observed closely related to the development of the planetary boundary layer and the mountain-valley breeze. BC mixing state, represented by the volume fraction of externally mixed BC to total BC (r), was retrieved by using the modified Mie model. The results showed r reduced from about 70% to 50% when the externally mixed non-BCs were considered. The periodical change and different diurnal patterns of r were due to the atmospheric aging and different air sources under different synoptic systems. Local biomass burning emissions were also one of the influencing factors on r. Aerosol radiative forcing for different mixing state were evaluated by a two-layer-single-wavelength model, showing the cooling effect of aerosols weakened with BC mixing state changing from external to core-shell mixture. (C) 2019 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

There is a large uncertainty in evaluating the radiative forcing from aerosol-radiation and aerosol-cloud interactions clue to the limited knowledge on aerosol properties. In-situ measurements of aerosol physical and chemical properties were carried out in 2012 at Mt. Huang (the Yellow Mountain), a continental background mountainous site in eastern China. An aerosol optical closure study was performed to verify the model outputs by using the measured aerosol optical properties, in which a spherical Mie model with assumptions of external and core shell mixtures on the basis of a two-component optical aerosol model and high size-segregated element carbon (EC) ratio was applied. Although the spherical Mie model would underestimate the real scattering with increasing particle diameters, excellent agreement between the calculated and measured values was achieved with correlation coefficients above 0.98. Sensitivity experiments showed that the EC ratio had a negligible effect on the calculated scattering coefficient, but largely influenced the calculated absorption coefficient. The high size segregated EC ratio averaged over the study period in the closure was enough to reconstruct the aerosol absorption coefficient in the Mie model, indicating EC size resolution was more important than time resolution in retrieving the absorption coefficient in the model. The uncertainties of calculated scattering and absorption coefficients due to the uncertainties of measurements and model assumptions yielded by a Monte Carlo simulation were +/- 6% and +/- 14% for external mixture and +/- 9% and +/- 31% for core-shell mixture, respectively. This study provided an insight into the inherent relationship between aerosol optical properties and physicochemical characteristics in eastern China, which could supplement the database of aerosol optical properties for background sites in eastern China and provide a method for regions with similar climate. (C) 2016 Elsevier B.v. All rights reserved.