Pollution Sources And Health Risk Assessment Of Polycyclic Aromatic Hydrocarbons?PAHs? In PM_2.5 In Urban Area Of Changping District,Beijing

Airborne fine particles(PM2.5)is one of the important fractions of atmospheric particulate matter and is a carrier for a variety of toxic and harmful pollutants.In recent years,China's atmospheric environmental problems have become increasingly prominent,and PM2.5 has become the primary air pollutant in most cities.Polycyclic aromatic hydrocarbons(PAHs)are a class of persistent organic pollutants with strong carcinogenicity and are more easily enriched in particles with smaller size.The alkyl-substituted PAHs(APAHs)are scarcely studied due to their low concentrations and many congeners in the atmosphere,which are difficult to analyze.Therefore,the study of PAHs and APAHs in PM2.5 is of great significance for Beijing to control toxic organic pollutants in the atmosphere and to protect the health of the population.In this study,gas chromatography/mass spectrometry(GC/MS)was used to measure 16 priority PAHs and 42 species of APAHs in PM2.5 in urban area of Changping District,Beijing.The concentrations,compositions and seasonal variations of PAHs and APAHs in PM2.5 were discussed.The sources of PAHs and APAHs were apportioned using diagnostic ratios and Positive Matrix Factorization(PMF).The health risk resulting from inhalation exposure to PAHs and APAHs in PM2.5 were estimated using the toxicity equivalent quantity(TEQ)and incremental lifetime cancer risks(ILCRs)model.The main results are summarized as follows:(1)The concentration of PM2.5 in urban area of Changping District was in the range of 23.91 ?g/m3?549 ?g/m3 in the past 5 years.It presented a clear seasonal pattern.The highest concentration was found in winter and autumn,and was followed by that in spring,and the lowest concentration was in summer.The total concentration of 16 priority PAHs(?PAH16)and APAHs in PM2.5 respectively ranged from 0.86 ng/m3 to 88.79 ng/m3 and 0.79 ng/m3 to 36.42 ng/m3.Seasonal patterns are winter>autumn>spring>summer.The concentration of APAHs was generally lower than that of PAHs.(2)In PM2.5 samples collected in urban area of Changping District,the dominant species of PAHs are fluoranthene(FLUA),pyrene(PYR),chrysene(CHR),benzo(b)fluoranthene(BbF)and phenanthrene(PHE),accounting for 20.8%,18.9%,12.4%,12.2%and 8.6%,respectively.Compared with the parent PAHs,the concentration of APAHs were generally lower,although there were more species of APAHs.The concentration of alkyl-substituted naphthalene(ANAP)was the highest,accounting for 29%of the total concentration of APAHs,which was followed by that of alkyl-substituted pyrene(APYR)accounting for 22%of the total concentration of APAHs.The largest number congeners were detected for alkyl-substituted phenanthrene(APHE),which accounts for about 20%of APAHs.The concentrations of alkyl-substituted fluorene(AFLN)and alkyl-substituted chrysene(ACHR)were similar,both of which accounted for 12%of the total concentration of APAHs.The concentrations of alkyl-substituted fluoranthene(AFLUA)and alkyl-substituted anthracene(AAN)were the lowest,accounting for 5%and 0.7%,respectively.(3)The diagnostics ratio and PMF were used for pollution source identification.The results showed that the contribution of coal combustion source(37.5%)was the highest;the second important source was vehicle emission and its contribution was about 29.9%;the contribution of natural gas and biomass burning source was about 19.6%;the contribution of oil source(13.0%)was the lowest.(4)The back trajectory model(HYSPLIT)was used to identify the locations of the sources.The results showed that all the four seasons were affected by air mass from the northwest direction,especially in winter when almost all air masses came from the northwest.In addition to the air mass from the northwest,the spring was also affected by air mass from the northeast(33%)and the south(42%).In summer,Changping was mainly affected by the airflow from the southeast direction.In the autumn,it was affected by airflow from the north and northwest,accounting for 57%.It was greatly affected by local sources as well,accounting for 43%.(5)The TEQ of PAHs and APAHs in PM2.5 in Changping ranged from 0.057 ng/m3 to 7.006 ng/m3,and presented a clear seasonal pattern.The TEQ value in winter was much higher than those in other seasons.The TEQ contributed by the vehicle source is extremely high(about 0.5 ng/m3),which was 3 to 5 times that of the other three pollution sources.The ILCR of PAHs and APAHs in PM2.5 in Changping due to inhalation exposure was between 2.006×10-8?2.468×10-6,which is within the acceptable range.