PM_2.5-bound Typical Polar Organic Compounds In Dezhou City: Pollution Characteristics And Source Analysis

Atmospheric fine particulate matter(PM_2.5,aerodynamic diameter less than or equal to 2.5?m)pollution is still a major air polluttant in cities,especially in northern China.Polar organic compounds?POCs?are group of the most abundant water-soluble organic compounds in aerosol.Due to their water solubility and hygroscopicity,POCs played an important role in atmospheric chemistry which can affect atmospheric visibility,global climate,and human health.Many POCs can be used as tracers of specific pollution sources.The systematic study of the chemical composition,concentration level,spatial-temporal distribution,and source analysis of POCs in atmospheric particles,could provide effective scientific basis for pollution prevention and control,and the formulation of laws and regulations.In this study,200 atmospheric PM_2.5 filter samples at three sites?DC,LC,PY?in Dezhou from 2018 to 2019 were collected,and 43 typical polar organic compounds in the samples were systematically analyzed to study the Pollution status and characteristics of POCs in Dezhou from multiple perspective.The main conclusions are listed as follows:?1?The annual average concentration of saccharides in Dezhou is 579.7 ng/m3?range:30.6?1471.4 ng/m3?,of which anhydrosugars is the highest,followed by sugar alcohols and primary sugars.PCA-MLR analysis revealed that there were four sources of saccharides in Dezhou:biomass burning emissions,fungal spore emissions,plant emissions,and other sources.Correlation analysis suggests that biomass burning emissions was the main source of xylose,glycerol,and erythritol.Fungal spore emissions can contribute to fructose,sucrose,and erythritol in atmosphere.Among all saccharides,the concentration of biomass burning?BB?tracer levoglucosan is the highest,and its concentration level in Dezhou is higher than that in most cities in China,which further shows that PM_2.5 in Dezhou was greatly affected by biomass burning.Concentration in autumn and winter was much higher than that in spring and summer,likely due to the increase of crop straw burning and residential heating in autumn and winter.In addition,the concentration of primary sugars and sugar alcohols in summer in this study was lower than that in other seasons,which may be related to the biomass burning source of sugar and sugar alcohols,particle size distribution,and meteorological conditions.?2?The annual average concentration of SOA tracers in Dezhou is 14.8?2.6?80.4?ng/m³,mainly including biogenic secondary organic aerosol?BSOA?,isoprene and?-pinene oxidation products,and anthropogenic sources,toluene oxidation products.The concentration of BSOA in summer was significantly higher than that in autumn and winter.It can be account for the higher temperature and stronger light in summer and the emissions of these precursors and their photooxidation in the atmosphere are higher than in other seasons.The seasonal variation of toluene oxidation products is not significant,indicating that the emissions of benzene series in Dezhou are relatively stable.The ratio analysis shows that the ratio of the isoprene SOA tracers,2-methylbutaerythritol?MGA?/2-methylglyceric acid?MTL?in Dezhou is higher than that in other cities,indicating that NO_x has a greater impact in the formation the SOA formation of isoprene in Dezhou.The MGA/MTL ratio in autumn and winter is much higher than that in summer,which is consistent with more biomass burning activities in autumn and winter,indicating that biomass burning has an important impact on isoprene SOA.The PA/MBTCA ratio was greater than 1 in winter,indicating that?-pinene SOA was more aged in Dezhou during summer than autumn and winter.Correlation analysis showed that the correlation of toluene SOA tracer 2,3-dihydroxy-4-oxopentanoic acid with BSOA tracers was not obvious.It showed that the polar organic compounds in PM_2.5 were derived from two different sources,natural and anthropogenic.?3?The average concentration of carboxylic acid?saturated linear dicarboxylic acids,aromatic acids and oxycarboxylic acids?in Dezhou is 163.8?15.6?411.5?ng/m3,of which the concentration of azelaic acid,glyceric acid and malic acid is the highest.Saturated linear dicarboxylic acids and aromatic acids have higher concentrations in autumn and winter.On the one hand,it was related to meteorological factors,including less precipitation,lower mixing layer height,and lower temperature inversion layer.On the other hand,due to the impact of increased biomass burning in autumn and winter,the correlation analysis with levoglucosan further confirmed the effect of biomass burning on organic carboxylic acids in Dezhou aerosols.The oxycarboxylic acids was mainly a product of secondary photooxidation.Due to the secondary generation mechanism and the complexity of the sources,the seasonal and spatial variation of each compound varies widely.From the analysis of the characteristic ratio,the ratio of adipic acid and phthalic acid to azelaic acid?C6/C9 and Ph/C9,0.42 and 1.17 respectively?with other cities,it was known that aerosol in Dezhou was mainly affected by anthropogenic emissions,which is different from cities in southern China,which generally have a lower ratio and a greater contribution from biological sources.?4?Correlation analysis between target organic compounds and meteorological parameters showed that temperature is the meteorological parameter that has the greatest influence on POCs in PM_2.5 in Dezhou,while humidity and wind speed had little effect on the mass concentration of POCs in PM_2.5.Correlation analysis with conventional pollutants showed that anthropogenic sources have a greater impact on saccharides and carboxylic acids in Dezhou.