Mass Spectrometry And Spectrum Studies Of The Products Of Ammonium Sulfate/Glyoxal Aqueous Phase Reaction

Atmospheric aerosols have a major impact on global or regional climate change,air quality and human health.It is also one of the important incentives for increasing regional ash.Among them,secondary organic aerosol(SOA)plays an important role in atmospheric aerosols.Understanding the formation and evolution of SOA is a critical step in accurately assessing the environmental impact of aerosols.The traditional gas-grain distribution theory model is very different from the SOA content in the atmosphere,and the generation of SOA is underestimated.Recent studies have shown that the water phase process can generate SOA,and in some areas its contribution is even comparable to the traditional gas phase process,thus becoming a research hotspot.Ammonium sulfate aerosol is the most widely distributed hygroscopic particulate matter in the atmosphere.Glyoxal is not only widely distributed in the atmosphere,but also has a high Henry coefficient in the aqueous phase,which can be transferred to the aqueous phase by gas-liquid distribution.Glyoxal-ammonium sulfate will form organic acids,oligomers,esters and imidazoles in cloud,fog and aqueous phase aerosols by reaction such as photooxidation and acid catalysis.After evaporation of water,low volatile substances are retained.SOA is formed in the particulate phase.The ammonium sulfate/glyoxal system is the most typical aqueous phase reaction system in the atmosphere.At present,the system is mainly studied by off-line method.It is found that the imidazoles in the aqueous phase SOA produced by the aqueous phase reaction can change the optical properties of the aerosol,and the formation of imidazoles can occur in any a-dicarbonyl compound and In the reaction of aldehydes,it has a universal significance.Because the water phase reaction has many influencing factors,the reaction process is complicated,and the yield of imidazoles is extremely low,accounting for about 1%of the total amount of SOA in the aqueous phase.Therefore,the research on the imidazoles in the aqueous phase SOA of this system needs further development.In this paper,a combination of aerosol laser time-of-flight mass spectrometry(ALTOFMS),simultaneous radiation vacuum ultraviolet photoionization mass spectrometry and other online mass spectrometry(TD-VUV-TOF-PIAMS),high performance liquid chromatography-electrospray ionization mass spectrometry(HPLC)-ESI-MS)and other off-line mass spectrometry,as well as liquid waveguide capillary(LWCC),total organic carbon analyzer(TOC)and other measurement techniques,respectively,for seven imidazoles(imidazole,imidazole-2-formaldehyde,2-methylimidazole,4-methylimidazole,1-ethylimidazole,2-ethylimidazole,1-n-butylimidazole)and the ammonium sulfate-glyoxal aqueous phase reaction product was studied.The mass spectrometric fingerprint information of imidazoles was established to identify the specific imidazole species contained in the aqueous phase reaction products,further supplementing and perfecting the aqueous phase process and reaction mechanism.The deeper understanding of the more complex aqueous SOA formation mechanism by studying the aqueous phase reaction of ammonium sulfate/glyoxal is of great significance for the accurate evaluation of SOA contribution and nighttime atmospheric chemical reactions.The research content of this paper mainly includes the following parts:1.On-line mass spectrometry analysis of the imidazole and ammonium sulfate/glyoxal aqueous reaction products by Aerosol Laser Time-Of-Flight Mass Spectrometry(ALTOFMS).The positive and negative ion mass spectra of seven imidazoles were measured,and the mass spectrometric fingerprint information of these imidazoles was obtained.Further,it is used to identify an imidazole substance in the ammonium sulfate-glyoxal aqueous phase reaction product.Through the combination of the ALTOFMS characteristic peaks of the imidazole sample,the aqueous phase of glyoxal/ammonium sulfate can be resolved to form an imidazole.2.Using a thermal desorption/tunable vacuum ultraviolet time-of-flight photoionization aerosol mass spectrometer based on synchrotron radiation source(TD-VUV-TOF-PIAMS)for seven imidazoles and ammonium sulfate/glyoxal aqueous reaction products Mass spectrometry was performed and the photoionization efficiency curve of each imidazole was given.This ionization mode primarily yields a mass spectrum containing intact parent peaks.The mass spectrum of the glyoxal/ammonium sulfate solution spray aerosol was identified using the fingerprint of the above standard sample.According to the mass spectrometric characteristics of the imidazole sample under different photon energies,it was confirmed that the imidazoles formed by the above aqueous phase reaction contained imidazole and imidazole-2-formaldehyde.3.High performance liquid chromatography-electrospray ionization mass spectrometry(HPLC-ESI-MS)was used to measure the aqueous phase of ammonium sulfate/glyoxal.The chromatographic and mass spectrometry were used to identify the imidazoles in the product.Thus,the imidazole,imidazole-2-carbaldeh yde in the imidazole sample was determined in the product,and biimidazole,hydrated imidazole-2-formaldehyde,hydrated imidazole-2-formaldehyde substituted by glyoxal,and some macromolecules were also identified.The off-line method was used to identify the rich imidazole species,and the reaction mechanism of the imidazoles in the aqueous phase reaction system was further verified and improved.4.The optical absorption spectrum of the imidazoles and the ammonium sulfate-glyoxal aqueous solution was measured using LWCC-TOC.The light absorption fingerprint spectrum of imidazoles was established,and the quantitative detection of the intensity of light absorption spectra was realized.The fingerprint was used to identify the imidazoles contained in the ammonium sulfate-glyoxal aqueous phase product,and it is speculated that the aqueous phase reaction product may contain imidazole-2-formaldehyde.