Diverse Mixing States Of Trimethylamine And Diethylamine In Typical Urban Atmospheric Particles

Amines are ubiquitous organic components in aerosols.Due to highly water-soluble and strong alkaline properties,amines significantly affect the hygroscopicity and acid-base balance of aerosols.The formation processes of particulate amines are commonly associated with the gas-to-particle partitioning of gaseous amines and acid-base reactions in the particles.Therefore,ambient relative humidity（RH）,temperature（T）,particle acidity,amine-ammonium exchange and oxidant all affect the formation of particulate amines.The quantitative studies of amines in field observation mainly focuses on source,diurnal and seasonal distribution characteristics of amines.Due to the lack of online quantitative analysis,it is hard to study the formation process of amines through high-resolution observation.In recent years,single particle mass spectrometry has the characteristics of on-line observation of the mixing states of amines.This technology can intuitively detect the chemical components mixed with amines,and analyze the relative abundance and mixing state of several low molecular weight amines by real-time observation in different environments to explore the formation of them.The study of mixing state is of great help to explain the source,acidity and aqueous reactions of amine-containing particles,but the mixing state of different amine-containing particles in the same atmospheric environment and the influencing factors of different particulate amines have not been thoroughly studied.Therefore,it is of great significance to further explore the mixing state.In this work,the mixing states of TMA-and DEA-containing single particles were investigated using a high-performance single particle aerosol mass spectrometer（HP-SPAMS）located in Nanjing during autumn and in Guangzhou during winter.Both of them showed the different distribution characteristics in the two cities under different atmospheric conditions,which confirmed the different mixing states of TMA-and DEA-containing particles.In this study,the effects of environmental relative humidity,particulate acidity,ozone concentration and nocturnal nitrogen chemical processes on the mixing state of TMA-and DEA-containing particles were discussed,and the heterogeneous formation process of DEA-containing particles at night and the photodegradation process during the day were analyzed.In addition,PMF was used to complement particulate TMA and DEA analysis and the chemical components closely related to the formation of TMA and DEA were analyzed.The conclusions of this study were as follows.（1）The number fractions of amine-containing particles in the two cities were as follows:particulate TMA,particulate DEA and particulate TEA accounted for 22.8%,5.5%and 3.7%in the total detected particles in Nanjing,respectively;particulate MA,particulate TMA and particulate DEA accounted for 23.8%,8.0%and 4.2%in the total detected particles in Guangzhou,respectively.The counts and abundance of the TMA-containing particles in total particles notably increased with enhancement of ambient relative humidity（RH）,while the DEA-and MA-containing particles showed no increase under high RH.The results suggested that RH was an important factor for the formation of particulate TMA,but not a decisive factor for the formation of particulate DEA（2）Significant enrichments of secondary organic species,including ⁴³C₂H₃O⁺,²⁶CN^-,⁴²CNO^-,⁵⁹C₂H₃O₂^-,⁷³C₃H₅O₂^-,and ⁸⁹HC₂O₄^-,were found in DEA-containing particles.The number fraction of DEA-containing particles was the lowest in the afternoon and increased rapidly at night.Combined with the distribution of the concentration of NOx,secondary organic species and nitrate to predict the formation of particulate DEA.Oxalate and glyoxylate are oxidation products of various organic matters,in the daytime the decrease of DEA-containing particles was observed as the enrichment of oxalate and glyoxylate and the increase of O₃ concentration in Guangzhou,which suggested a substantial impact of photochemistry on the aging process of DEA-containing particles.The relative abundance of nitrogenous organic matter(²⁶CN^-and ⁴²CNO^-)like oxalate and glyoxylate also increased at noon,but oxalate and glyoxylate has fallen sharply at nighttime,and the abundance of nitrogenous organic remain high,and the enrichment of nitrate in the night,that the formation of DEA particles might be associated with reactions of gaseous DEA with HNO₃ and/or particulate nitrate（3）The PMF analysis showed that particulate DEA was mainly connected with sulfate factor,nitrate factor and organic nitrogen factor.TMA was mainly related with ammonium factor and sulfate factor.In addition,the organic nitrogen factor and nitrate factor of DEA-containing particles had an obvious upward trend at night,which further suggested that DEA-containing particles were associated with the reaction of gaseous nitric acid or nitrate at night.（4）The MA-,TMA-,and DEA-containing particles were further classified into 4 groups,which showed MA and TMA mainly distributed in the elemental and organic carbon（ECOC）type particles while DEA in the organic carbon（OC）type particles in Guangzhou.It was consistent with the mixing states characteristics of TMA-and DEA-containing particles,indicating that DEA-containing particles have potential significance to study the process of SOA.In all,based on the analysis of the mixing states of TMA-and DEA-containing single particles in the two cities,the formation of TMA-containing particles was mainly influenced by RH,while DEA-containing particles were enriched with secondary components.Particulate DEA formation at nighttime was mainly associated with heterogeneous reaction,and particulate DEA were reduced by photolysis during the period of strong photochemistry in the daytime.The different mixing states and formation processes of the TMA-and DEA-containing particles in the same atmosphere indicate the importance of the of mixing state on the formation processes of secondary organic aerosols and provide a new idea for the further analysis.