Establishment And Preliminary Application Of Nano-Hygroscopic Tandem Differential Mobility Analyzer(Nano-HTDMA) System

Hygroscopicity is one of the main properties of aerosols.In order to evaluate the impact of aerosol particles on environment,climate and health,it is necessary to understand their hygroscopicity under different relative humidity(RH).Up to now,although the hygroscopicity of some pure inorganic salts or salt mixtures with particle size greater than 100 nm has been extensively studied,the research on nuclear mode fine particles(which diameter is generally less than 30nm)is still relatively scarce.With the development of research,it has been found that the hygroscopicity of ultrafine aerosol particles(for example,less than 30nm)exhibits different evolution characteristics from that of large size aerosol particles.Moreover,by measuring the hygroscopic growth factor(g)of ultrafine nanoparticles,the possible chemical composition of particles can be determined indirectly,which will contribute to deeper understanding on the initial nucleation mechanism of atmospheric aerosols.In view of the importance of hygroscopicity of ultrafine nanoparticles(<30 nm),a Nano-HTDMA system has been designed and developed.And a series of studies have been carried out on the hygroscopicity of several typical inorganic salt nanoparticles.This paper mainly achieves the following research results:1).In order to study hygroscopicity of aerosol particles with particle size less than 30 nm,a Nano-HTDMA system was built based on the commercial Nano-DMA.Moreover,a control and acquisition software is developed based on Labview platform,which leads to the humidity automatic control and on-line data acquisition.Under room temperature,the range of aerosol humidification can be controlled between 20%-90%RH for the system,and the range of fluctuation after stabilization is ±0.5%.Generally,it takes about 10 minutes to measure the hygroscopicity growth factor under one RH condition.The overall uncertainty of the measurement g factor is±2.1%and the error mainly comes from the measurement deviation of temperature and humidity sensors.After calibration and verification,it is proved that the system is qualified for study on the hygroscopicity of nanoparticles.2).The hygroscopicity growth curves of sodium chloride,ammonium sulfate and potassium iodide particles with diameters of 30,20 and 15 nm were measured by the home-made Nano-HTDMA system.By comparison with the theoretical model calculation results,the hygroscopicity of the three typical inorganic nanoparticles were systematically studied.It was found that the g factors of these systems decrease with the decrease of diameter(dm)under the same RH due to Kelvin effect.And it was shown that the DRHs of sodium chloride and potassium iodide particles are related to the corresponding particle sizes,that is,their DRH will increase with the decrease of the diameter of the particles.While for ammonium sulfate particles,no particle size correlation was found,and the DRH is almost the same for particles with different size.In general,the experimental g factor of sodium chloride and ammonium sulfate particles with different particle sizes showed good consistency with the corresponding theoretical values.However,the experimental and the theoretical g factors of different particle sizes of potassium iodide did not agree with each other.It is proposed that the disagreement maybe result from the uncertainty of the physical parameters used for theoretical calculation of the KI hygroscopic growth factor.