The hygroscopicity and optical properties of alkylaminium sulfates （AASs） were investigated using a hygroscopicity tandem differential mobility analyzer coupled to a cavity ring-down spectrometer and a nephelometer. AAS particles do not exhibit a deliquescence phenomenon and show a monotonic increase in diameter as the relative humidity （RH） ascends. Hygroscopic growth factors （GFs） for 40, 100 and 150 nm alkylaminium sulfate particles do not show an apparent Kelvin effect when RH is less than 45%, whereas GFs of the salt aerosols increase with initial particle size when RH is higher than 45%. Calculation using the Zdanovskii-Stokes-Robinson mixing rule suggests that hygroscopic growth of triethylaminium sulfate-ammonium sulfate mixtures is non-deliquescent, occurring at very low RH, implying that the displacement of ammonia by amine will significantly enhance the hygroscopicity of （NH4）2SO4 aerosols. In addition, light extinction of AAS particles is a combined effect of both scattering and absorption under dry conditions, but is dominated by scattering under wet conditions.
In this study,hygroscopicity of size-segregated ambient submicron particles in urban Hangzhou was studied from 28th December 2009 to 18th January 2010,using a hygroscopicity-tandem differential mobility analyzer(H-TDMA).The submicron particles in Hangzhou showed a minor hygroscopic growth at 73%relative humidity(RH),and then grew significantly between 77%and 82%RH.Monomodal distribution accounted for 90%for 30 nm particles,17%for 50 nm particles,and less than 7%for particles larger than 50 nm at 82%RH.Deconvolution of the bimodal distribution indicated a less hygroscopic group and a more hygroscopic group,with the fraction of the more hygroscopic group increasing with the initial dry particle size and then remaining almost constant for accumulation mode particles.Our results imply that submicron particles in urban Hangzhou were almost entirely externally mixed,and the hygroscopic properties of ambient particles in urban Hangzhou were mainly a function of their size and chemical composition.
The air quality model system RAMS （Regional Atmospheric Modeling System）-CMAQ （Models-3 Com- munity Multi-scale Air Quality） coupled with an aerosol optical/radiative module was applied to investigate the impact of different aerosol mixing states （i.e., externally mixed, half externally and half internally mixed, and internally mixed） oil radiative forcing in East Asia. The simulation results show that the aerosol optical depth （AOD） generally increased when the aerosol mixing state changed from externally mixed to internally mixed, while the single scattering albedo （SSA） decreased. Therefore, the scattering and absorption proper- ties of aerosols can be significantly affected by the change of aerosol mixing states. Comparison of simulated and observed SSAs at five AERONET （Aerosol Robotic Network） sites suggests that SSA could be better estimated by considering aerosol particles to be internally mixed. Model analysis indicates that the impact of aerosol mixing state upon aerosol direct radiative forcing （DRF） is complex. Generally, the cooling effect of aerosols over East Asia are enhanced in the northern part of East Asia （Northern China, Korean peninsula, and the surrounding area of Japan） and are reduced in the southern part of East. Asia （Sichuan Basin and Southeast China） by internal mixing process, and the variation range can reach ＋5 W m 2. The analysis shows that the internal mixing between inorganic salt and dust is likely the main reason that the cooling effect strengthens. Conversely, the internal nfixture of anthropogenic aerosols, including sulfate, nitrate, ammonium, black carbon, and organic carbon, could obviously weaken the cooling effect.
The regional air quality modeling system RAMS （Regional Atmospheric Modeling System）-CMAQ （Community Multi-scale Air Quality modeling system） is applied to analyze temporal and spatial variations in surface ozone concentration over Beijing and its surrounding region from July to October 2008.Comparison of simulated and observed meteorological elements and concentration of nitrogen oxides （NOx） and ozone at one urban site and three rural sites during Olympic Games show that model can generally reproduce the main observed feature of wind,temperature and ozone,but NOx concentration is overestimated.Although ozone concentration decreased during Olympics,high ozone episodes occurred on 24 July and 24 August with concentration of 360 and 245 μg/m 3 at Aoyuncun site,respectively.The analysis of sensitive test,with and without emission controls,shows that emission controls could reduce ozone concentration in the afternoon when ozone concentration was highest but increase it at night and in the morning.The evolution of the weather system during the ozone episodes （24 July and 24 August） indicates that hot and dry air and a stable weak pressure field intensified the production of ozone and allowed it to accumulate.Process analysis at the urban site and rural site shows that under favorable weather condition on 24 August,horizontal transport was the main contributor of the rural place and the pollution from the higher layer would be transported to the surface layer.On 24 July,as the wind velocity was smaller,the impact of transport on the rural place was not obvious.
