Preliminary Analysis Of Physical And Chemical Characteristics And Sources Of Atmospheric PM_2.5 In Typical Areas Of Beijing

With the growth of economic and the intensification of urbanization,the pollution of urban atmospheric particulates is also frequent.At present,the primary pollutant of atmospheric environment of our country is PM,especially the PM_2.5 that the aerodynamic diameter is less than 2.5μm exceeds standard seriously in most large and medium-sized cities of our country.At the same time,Atmospheric fine particulates(PM_2.5)which are crucial factors resulting in haze,have significant effect on human health and climate change and have become the most serious atmospheric environment problems in China.So urban air particulate pollution has become a hot research topic both at home and abroad.In this research,chose Beijing as the object of study A location near West-Three-Ring Road,a typical traffic belt in Beijing City,was chosen as the sampling site.The Weight Method and Light Scattering Method were applied to measure PM_2.5mass concentration.According to the U.S.EPA performance index and certification methods of artificial sampling measurement comparison for PM_2.5 continuous monitoring system,in combination of the current related technical specifications in China,Parallelism test and linear regression were used for analysis of availability and comparability between the data resulting from the two methods;and to study the concentration,season characteristics and main sources of organic carbon（OC）and element carbon（EC）in PM_2.5 in Beijing urban area;Atmospheric PM₁₀0 and PM_2.5samples were collected at four location（milu park,west sanhuan,garden north road,changping rural）during four typical air pollution episodes in spring and winter of 2015in Beijing.10 kinds of water-soluble ions,organic carbon（OC）and elemental carbon（EC）,16 kinds of polycyclic aromatic hydrocarbons（PAHs）and 7 kinds of heavy metal element were analyzed.The results were as follows:（1）The standard deviation of PM_2.5 mass concentration measured by gravimetric method was lower than 5μg·m^-3,and met the requirements of quality control measures of HJ655-2013.The relative standard deviation by light scattering method was lower than 11%,and met the requirements of quality control measures of EPA PART 53.PM_2.5mass concentration measured by gravimetric method and those by light scattering method in four seasons were all well correlated（correlation coefficient≥0.95）,but the slope and intercepts of the correlation formula were varied.The slopes were all higher than 1 in four seasons,with the highest slope above 1.50 in winter.The intercepts in four seasons were in the range of 11.05-25.04μg·m^-3,with the higher value as>24 in spring and winter.（2）A total of 95 PM_2.5.5 sample were collected seasonally in traffic belt of West Third Ring of Beijing from April 2015 to March 2016.OC and EC were analyzed by thermal optical reflection（TOR）,and the characteristics including OC/EC ratios,correlations between OC and EC,secondary organic carbon（SOC）and the source of OC and EC were discussed in detail.Results showed that the average concentration of PM_2.5.5 was（109.9±7.99）μg·m^-3.The average concentration of OC and EC were（13.49±4.32）,（5.41±1.83）μg·m^-3,accounting for 13.13%and 5.2%of PM_2.5,respectively.The seasonal characteristics of the average concentrations and proportions of OC and EC in PM_2.5.5 were ranked by the order of winter>autumn>spring>summer.The ratios of OC/EC in four seasons were all larger than 2.0,which indicated that the SOC were formed.The minimum OC/EC ratio method was used to estimate the SOC formation.The annual average concentration of SOC were（6.88±1.10）μg·m^-3,accounting for50.86%of OC.The concentration of SOC during winter and autumn were higher than that in spring and summer.The highest contribution of SOC to OC occurred as 62.22%in summer.The correlation analysis showed that OC and EC were more correlated in spring（R²=0.9046）and autumn（R²=0.8886）than in summer（R²=0.4472）and winter（R²=0.6018）,indicating that the emission sources were similar and relatively simple in spring and autumn.By analyzing the mass concentration of eight kinds of carbon components in PM_2.5,gasoline vehicle emissions and coal burning were indicated to be the major sources of atmospheric carbon aerosols in urban of Beijing.（3）The maximum daily mass concentration of PM_2.5 was 240.3μg·m^-3.In addition the average daily mass concentration of PM_2.5.5 was 93.5μg·m^-3,exceeding the ambient air quality standards（GB3095-2012）of china.In the 36 groups of samples,PM_2.5 exceed the standard value by 61.1%.NO₃^-,SO₄^2-and NH₄⁺were the most important water soluble ions in particulates.Most of the water soluble ions mainly exist in the fine particles,especially the secondary particles NO₃^-,SO₄^2-and NH₄⁺.On the contrary,the Ca²⁺is almost in the coarse particles.The ratios of NO₃^-/SO₄^2-in four sites were all larger than 1.0,which indicated that the SO₂ and NOx were mainly derived from mobile sources.The average values of OC/EC in PM_2.5 was 3.7-6.7,which indicated that particulates in four functional areas have the secondary organic carbon（SOC）pollution.The primary monomers of PAHs were 4-6 rings in atmospheric particulate in the four functional areas.The concentration of Zn and Mn in the four functional areas were found to be the highest among heavy metals elements in PM_2.5,followed by Cu and Cr.The dominant emission sources to the formation of four typical air pollution were soil dust,transportation,coal burning and secondary organic aerosols,based on the analytic of Chemical components and pollution characteristics of PM_2.5.5 in four functional areas.In addition,the contributions of other sources are biomass burning,cooking emissions,livestock and poultry raising.