Influence Of Secondary Organic Aerosols On Hygroscopicity Of Inorganic Salts In Particle Analysis

The interaction between atmospheric aerosol particles and water vapor in the air changes the aerosol particle size and the mixing structure,but may also cause heterogeneous chemical reaction,making the chemical composition of the particulates even more complex.So it is of great significance to take an in-depth research on the hygroscopicity of atmospheric aerosols.In general,atmospheric aerosols include both inorganic salts with strong hygroscopicity and secondary organic aerosols with relatively weak hygroscopicity.At present,numerous research woks have been done on the hygroscopicity of aerosols;however,the aerosol compositions involved in these studies are too simple to mimic the actual atmospheric particulates.In particular,whether and how secondary organic aerosols influence the hygroscopicity of inorganic salts has not been well understood.As such,there is a pressing need to explore how the complex secondary organic aerosols impact the hygroscopic behavior of inorganic salts.In this thesis,a production process of secondary organic aerosol by α-pinene was simulated in a laboratory by using a 2 L gaseous phase flow reaction tube.Specifically,ozone was used as the oxidizing agent and,as seed aerosols,sodium chloride and ammonium sulfate were put at the end of the flow reaction tube to collect the oxidants of α-pinene.The time of organic film absorption was 11,15,and 20 hours,respectively.Based on the aforesaid system,an individual particle system was then independently built so that,the influence of the secondary organic aerosols on the hygroscopic capacity of inorganic salts can be studied.Experiments showed that the samples with typical Na Cl core-organic shell and(NH4)2SO4 core-organic shell were successfully prepared by using the gaseous phase flow reaction device,and the thickness of the organic shell was directly proportional to the collection time duration.In addition,it is found that the organic matters could cause inorganics to absorb water vapor in advance,postpone their deliquescent point and inhibit the growth of core at high humidity.Moreover,the single particle analysis method was used to collect atmospheric aerosol particles from Lesser Khingan Mountains,located in the natural aerosol source region of China,and three cities(namely,Jinan,Hangzhou and Beijing)in the man-made aerosol source region.To study the location-related aerosol hygroscopicity,a detailed comparison of the real atmospheric hygroscopic behavior between different regions was carried out.Results showed that in Lesser Khingan Mountains,Hangzhou and Beijing,atmospheric particulates began hygroscopic growth under low humidity conditions(50%),with the completely deliquescent point of 83%～84%,while the atmospheric particulates in Jinan did not grow under low humidity condition until the humidity increased to 72%.The complete deliquescent point was found at 85%.Furthermore,by comparing the results of lab simulation and field observations,it was found that the hygroscopic behavior of the particles with secondary organic aerosol shell/inorganic salt core represented by α-pinene ozonized product is similar to the hygroscopic property of atmospheric particulates in Lesser Khingan Mountains.Therefore,the present research could provide a theoretical basis for further investigations related to the influence mechanism of secondary organic aerosols on the hygroscopicity of inorganic salts.