Pollution Characteristics Of Atmospheric Particulates In Northern Urban Beijing During Haze-fog And Non Haze-fog Periods

In recent years,particulate pollution under hazy weather in Beijing has aroused widespread concern,especially in urban areas where PM2.5 is predominant,resulting in increasingly serious air pollution.Therefore,the study of particulate pollution characteristics and harmful components under different meteorological conditions was conducted.In this paper,continuous sampling events was conducted in urban Beijing(2015-2016),the pollution characteristics of particulate matter in haze and non-haze conditions were studied from the perspective of concentration,particle size and composition.We explored the relationship between meteorological factors and the concentration and particulate in the whole year.The particle type,morphology,composition,and source of particulate were discussed through single particle analysis.The characteristics and sources of heavy metal and PAHs pollution in particles during the haze and non-haze stage were discussed.Finally,the impact of harmful components on targets of different populations was evaluated,providing a theoretical basis for the management of haze problems.The main conclusions are as follows:(1)Through analysis of 572 samples,we found that the average concentrations of PM2 5 and PM10 were 102.45?g/m' and 144.75?g/m3.PM2.5 concentration in haze period is about 1.7-5.0 times that of non-haze period.The ratio of PM2.5 to PM10 ranged from 0.76 to 0.84.The average ratio of PM2 5/PM10 in haze-fog period was 0.80.Fine particle was the main pollutant in this period.With relative humidity of 60%to 80%,the average concentration ratio of PM-2.5 to PM10 is 0.79.The enrichment of fine particulate matter in the high-humidity environment of Beijing urban area is more serious during haze period.(2)The relationship between relative humidity and P2.5 can be divided into three phases.During haze period,the relationship between PM2.5 concentration and relative humidity is positively correlated.When PM2.5 is moderately contaminated(70-100?g/m3),there is a positive linear relationship between them.When PM2.5 concentration is low(<70?g/m3),the relationship between PM2.5 and relative humidity is not obvious.There is a negative correlation between temperature and particulate concentration during haze period.Precipitation'removal efficiency for PM2.5 is higher than PM10.PM2.5 removal efficiency is highest in spring and summer.For urban PM10,the highest removal efficiency(46.28%)was in autumn,followed by summer,winter and spring.(3)Single particle in urban area can be identified as follows:fly ash,sootparticles,sulfate particles,silicate particles,and metal particles.The particles in haze period mainly consist of spherical fly ash and chain-like,fluffy dust aggregates.The fly ash is rich in O,Si,A1 and Ca.The urban fly ash particles were mainly originated from automobile exhaust and factory emissions.During haze period,the soot aggregates are mainly rich in C,accompanied by a small amount of Si,Al and S elements.The main source is the combustion emission.43%of sulphur rich mineral particles have significant vulcanization characteristics.(4)Through analysis of heavy metal,the highest average concentrations were observed in winter.Heavy metal concentrations in haze periods increased by 1.5 to 11 times compared with non-haze period.By analyzing the characteristics of PAHs contamination in PM2.5 during haze-fog period,we found that 4-ring PAHs homologues contributed the highest percentage of PAHs(52.33%)in the winter haze period,and low-ring PAHs contributed relatively higher in the summer.Combustion-derived PAHs are significantly higher in winter and spring.The combination of diagnostic ratios such as BaA/BaA+CHR and principal component analysis shows that the main source is traffic emissions,followed by combustion process emissions and mixed source.(5)Risk level caused by Cr in PM2.5 during the winter haze-fog period is the highest(1.80×10-4),and it has a certain risk of carcinogenesis for adults.The average risk level of Cr in haze-fog period is 18.60 times that of non-haze fog period.The toxicity level of 5-ring PAHs homologues in haze-fog period was 4.25 times that of 4-ring PAHs.The toxicity of PAHs in the particles was mainly affected by 5-ring PAHs homologues,and 75%-81%of TEQ values could be attributed to 5-ring PAHs.The BaP and BbF caused the highest risk,BbF in winter,and BaP in spring and winter may cause higher cancer risk to the environment and humans.The non-carcinogenic risk levels of 4-ring PAHs(PYR and FLT)were approximately 51 times that of 3-ring PAHs(FLR and ANT),and the non-carcinogenic risk was increasing with molecular weight and number of rings.