| In recent years,large-scale haze events occurred frequently in north China.The atmospheric environmental problems have been received extensive attention of the whole society.As one of the important pollutant in the atmosphere,atmospheric aerosols' composition,generation and transmission mechanism have raised widely focus in domestic and abroad because of its affects on atmospheric radiation,climate change and human health.Particularly,new particle formation(NPF)and aqueous secondary organic aerosol(aqSOA)were paid close attention.In this study,observation experiments were carried out in a typical background site in Shandong province,the Yellow River Delta to study the constituent,conversion and transmission of carbonaceous aerosol.Also,new particle formation events were investigated in a typical polluted city,Jinan in Shandong province.The results showed that there was heavy carbonaceous aerosol pollution in the Yellow River Delta during winter and formation was more responsible for haze formation in winter.Besides,haze formation was closely connected with long-distance transmission in the background site.NPF observation results demonstrated(particularly by the observation of particle size distribution under 3 nm)although previous studies suggested NPF cases mainly took place in relative clean region,however,several typical NPF events were also observed in polluted urban,and quite a few events appeared in early morning,on which time the solar radiation was not the strongest during one day.This appearance implied the NPF process in polluted area might be different from that in clean region,the oxidation of high concentration SO2 and VOC contributed significantly to NPF.In addition,haze formation had a affinity with NPF in polluted urban area based on the observation data.To further study the SOA formation mechanism,laboratory simulation on aqSOA formation was carried out in the Pacific Northwest National Laboratory(PNNL)based on the preliminary understanding of SOA formation,conversion and its contribution to haze events in the atmosphere.In this study,combination of System for Analysis at the Liquid Vacuum Interface(SALVI)and time-of-flight secondary ion mass spectrometry(ToF-SIMS)were used.Thus,direct detection of glyoxal-H2O2 oxidation products at the aqueous surface was available for the first time.Products distribution was illustrated by imaging technique(two-dimensional,2D and three-dimensional,3D)images)of the liquid surface and interface in addition to mass spectra.Contribution pathways of glyoxal oxidation to aqSOA was investigated at molecule level based on the experimental data analysis.In addition,A comparison between dry and liquid samples of glyoxal surface products by hydrogen peroxide was carried out in lab simulation study.The results showed glyoxal-H2O2 oxidation products at the aqueous surface had an important contribution to SOA formation.The observation of water cluster changes between dark and photochemical aging suggested that glyoxal oxidation affected the hydrophilcity/hydrophobicity at the surface,influencing the ability and subsequent conversion of SOA.Besides,glyoxal-H2O2 oxidation products were influenced by sample preparation based on the comparison between dry and liquid samples.It would be help for us to improve accuracy of aqueous surface analysis and investigate the SOA formation pathways under different conditions in the atmosphere.Our results demonstrated that the unique portable microfluidic reactor combined with liquid SIMS could be a powerful tool to investigate aqueous surface reactions in situ at the molecularlevel and fill in the knowledge gap of interfacial reactions involving liquids in atmospheric chemistry.Main results are as follows:Observation of carbonaceous aerosol:(1)Carbonaceous aerosols in PM2.5 samples in the Yellow River Delta were analyzed by a thermal/optical reflectance OCEC analyzer during winter(Jan 14-Feb 14),spring(April 1-May 3),summer(Jul 4-Jul 29),and autumn(Oct 11-Nov 7).The mean OC and EC concentrations were 7.61 ?g/m3 and 2.98 ?g/m3,respectively.This concentration was higher than densely inhabited district in China but lower than remote mountainous region in China and clean area abroad.The seasonal variations in OC exhibited the following order:winter>autumn>spring>summer.The variations in EC exhibited the following order:autumn>winter>summer>spring and the variations in SOC exhibited the following order:winter>spring>autumn>summer.Annual mass concentration showed that SOC contributed up to 48%to total OC concentration.(3.64/7.61 ?g/m 3).(2)Analysis of haze events showed that OC,EC and SOC were more responsible for haze formation in winter than other seasons.Strong correlations between OC and EC(R2= 0.83-0.97)suggested that these species had similar emissions and transport processes.Moreover,high OC/EC ratios in cold seasons implied that the OC originated from biomass burning in nearby rural areas or transport from other areas.Analysis of back trajectories showed that the Yellow River Delta was considerably affected by local haze events,and an air mass that travelled through the Bohai Rim contributed the highest carbonaceous aerosol concentration,except in summer haze episodes.According to all samples,the air masses travelled through polluted areas,such as Beijing and Hebei Province,which typically had the highest average OC and EC concentrations in China,implied the OCEC concentration was affected by the Bohai Rin transmission,Observation of new particle formation in Jinan:(1)Particle number distribution was observed from 6 October to 10 December 2013 in polluted urban Jinan,North China by using Neutral cluster and Air Ion Spectrometer(NAIS)and Wide-range Particle Spectrometer(WPS).During 62 sample days,10 new particle formation(NPF)events were observed,half of them occurred in early morning around 9 o'clock,others were observed on the noon,which solar radiation was the strongest during one day.The observed formation rate of new particles(J)and growth rate(GR)were 7.06-636.9 s-1cm-3,0.94-5.8 nmh-1 respectively.Compared with other sites,the formation rate in Jinan was higher than other urban area and the growth rate was close to them.However,both formation and growth rates were much higher than clean district.(2)The characteristic of NPF in polluted area was different from that in clean area.Because of traffic peak in the early morning,a large amount VOC was released,with high concentration of sulfuric acid,this two "helper molecular" may cause NPF in early morning,in which time the solar radiation was not very high.In addition,sharply rising of PM1 was observed after NPF events,indicated haze might be closely related to the growth of large-size particle.(3)Sulfuric acid only contributed about 10%of total formation rate in most events by calculation,suggested the contribution of VOC can not be ignored in polluted urban atmosphere.The VOC oxidation at aerosol surface could help critical nucleus break through the first nucleation(about 1.5 nm)and second nucleation barrier(about 3 nm),then particle growth becomes spontaneous.This inference was accordance with that particles between 1.5-3 nm occupy most of total number concentration.The NPF events would not be observed if this part particle can not grow exceed 3 nm.Laboratory simulation on glyoxal and hydrogen peroxideaqueous surface reaction:(1)To further study the mechanism of SO A formation,aqueous surfaces reactions on atmospheric aerosol and droplet of glyoxal and hydrogen peroxide(H2O2)have been studied by a microfluidic reactor(SALVI)coupled with in situ ToF-SIMS.Direct detection of the liquid surface oxidation products was available for the first time.Reaction products were observed at molecule level by spectrum,spectral principal component(PCA),2D and 3D analysis.Various photochemicalaging(15 min,30min,1 hr.,2 hr.,and 4hr.)and dark reactions(1 hr.,2 hr.and 5 hr.)products,pathways and their contribution to aqSOA formation were also investigated.(2)ToF-SIMS provided observations of glyoxal hydration(i.e.first and secondary products,dimers,trimers),oxidation products(i.e.,glyoxylic acid,oxalic acid,formic acid,tartaric acid),oligomers,cluster ions,and water clusters with sub-micrometer spatial resolution.Observations of oxidation products gave the experimental foundation to deduce new reaction pathways at the aqueous surface.Different products were detected under different conditions,show that glyoxal-H2O2 oxidation reaction at the aqueous surface was affected by irradiation and aging.By using liquid SIMS,some new oligomers and cluster ions were observed besides the traditional products reported by previous studies.The first observation of water cluster changes between dark and photochemical aging.In detail,more large water clusters existed in UV aging,suggesting that such surface aging tends to be more hydrophobic.In contrast,the surface which had undergone dark reactions could be more hydrophilic.This result provide the information that glyoxal oxidation could affect the hydrophilcity/hydrophobicity and water microenvironment at the surface,influencing the particle's ability in reactive uptake and subsequent cloud condensation nucleation and/or ice nucleation activation.(3)It was confirmed that the products in dry samples were impacted by the sample preparation process based on the spectral and PCA analysis.In detail,carboxylic acids,cluster ions,hydration products and oligomers were mainly observed in liquid samples;different carboxylic acids and oligomers in the dehydrated form were more likely to occur in dry samples.Although dry sample analysis provides high mass accuracy and peak resolution compared to the current in situ liquid SIMS approach with unit mass resolution,moreover,dry samples revealed some products during aqueous evaporation process,it was also necessary to employ the liquid-SIMS approach to investigate aqueous surface reactions because the liquid samples provided more viable observations of surface reactions in the aqueous phase relevant to atmospheric chemistry. |
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