| Environmental pollution has already become one of the most urgent problems that restricts the economic and social development of China.And high level of aerosol particles is one of the major characteristics of this severe complex atmospheric pollution,its physical-chemical properties are crucial to the environment and radiation effect,and have gain most attention in both environmental and climatological fields.The hygroscopicity of aerosol particles can significantly affect their size,optical properties,cloud condensation nuclei(CCN)activity and chemical reactivity,thereby having an important impact on the atmospheric visibility,radiation forcing,acid deposition and human health directly or indirectly.Black carbon is generally regarded as the high-content light absorbing component of atmospheric aerosols.Its light absorption properties are closely related to the mixing state of black carbon.Due to the complexity of the environmental aerosol,the mixing state of black carbon and hygroscopicity of particles are two key factors which introduce great uncertainties in estimating aerosol direct radiative forcing.A volatility hygroscopic tandem differential mobility analyzer(VH-TDMA)was designed and constructed to allow rapid measurement of hygroscopic properties and thermal properties of aerosol particles:the heating unit is equipped with four symmetric columns kept a temperature between 25? and 350? that allowed the heating temperature to be rapidly changed so that a higher temporal resolution can be achieved comparing to a regular V-TDMA,and the humidification unit allows to measure the hygroscopic behavior of the aerosol in the range of 10%-90%RH(relative humidity).Based on laboratory experiments,the reliability and accuracy of the system was verified by using the standard laboratory aerosol generator.It was tested in the field during a research campaign with some first results.The results indicate that the VH-TDMA system is an excellent and powerful tool for studying the volatility and hygroscopic behavior of aerosols and meeting the demand required for laboratory research and fieldwork on atmospheric aerosols.The hygroscopic properties of two water-soluble organic compounds(WSOCs)relevant to urban pollution(oxalic acid and succinic acid)and their internally mixtures with inorganic salts(ammonium sulfate and ammonium nitrate)are investigated using the H-TDMA under the relative humidity between 10%and 90%.Zdanovskii-Stokes-Robinson(ZSR)and Extended Aerosol Inorganic Model(E-AIM)were used to predict the hygroscopic growth factor,and compare with the experimental results.The results demonstrate that the coexisting hygroscopic species have strong influences on the phase state of particles,thus affecting chemical interactions between inorganic and organic compounds and the overall hygroscopicity of mixed particles.Then,the volatility tandem differential mobility analyzer(V-TDMA)was used to measure the mixing state(internally mixed number fraction)of the size-resolved(50-350 nm diameter)BC-containing particles(at 300?)at a rural site(ShouXian)in China in June and July 2016.The measured average number fractions of HV,MV and LV particles showed an obvious correlation to the selected size.The results indicated that externally mixed BC particles mainly concentrated on small size range,and the higher values of MV and LV in the larger selected sizes may be due to the well aged particles arriving at the rural background site.Fully concentrated relative frequency distributions and obscure diurnal variations of size-selected Fin,indicated that the transported air masses have similar aging stage to local emission sources.Comparing with previous studies,the different values and size-dependent trend of Fin are observed,resulting from competing effects of both direct emissions and aging process.Distinct difference was observed among the spatial distributions of PSCF values for size-resolved Fin,indicating that the distinguishing potential contribution sources for internally mixed BC-containing particles with different sizes.The findings also implies that transport plays a predominant role in deciding the BC mixing state in Shouxian site,and shows size-dependent relationship.Finally,the hygroscopic properities of sub-micrometer aerosol particles at 90%relative humidity were studied in Shouxian in the early July,2016.Hygroscopic diameter growth factors were measured with H-TDMA for dry particle diameters between 50 to 250 nm.The statistical results show that the GFs of the aerosol present a distinct bimodal or unimodal distribution.For the less-hygroscopic component,the average growth factor(GF)is 1.07,and for more-hygroscopic compound,the GF was between 1.373?1.560 and positively correlated with the particle size.After humidification,the average spectral distribution of the peak value of the local polydisperse aerosol showed a slight increase with bimodal distribution,indicating the hygroscopic ability of different diameter particles are different,and the proportion of less-and more-hygroscopic component are also different.The difference between the spectral distribution of aerosols at different time(day and night)reflects the different source of aerosols.The less-hygroscopic component mainly come from local emissions and the more-hygroscopic component mainly come from distance transport. |
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