常州夏秋季PM2.5中碳质气溶胶特征及来源

Characteristics and Source Identification of Carbonaceous Aerosols in PM_(2.5) Measurements During Summer and Fall in Changzhou

为更好地了解碳质组分的特点和来源,在常州市采集了夏季(7~8月)和秋季(10~11月)60个细颗粒物(PM_(2.5))样品.采样期间,夏季PM_(2.5)、OC、EC平均浓度分别为73.0、14.3和3.3μg·m^(-3),秋季为84.2、13.2和3.5μg·m^(-3).总碳质组分(OC+EC)占PM_(2.5)总质量的24.3%(夏季)和20.7%(秋季).采用IMPROVE-A热/光反射法测定的碳质8组分结果表明,OC2、OC3、OC4和EC1相关性好(r>0.92),EC2和EC3相关性较好(r>0.65),说明可能的相似来源.OC与EC相关性中等,表明碳质组分来源复杂.秋季WSOC/OC(60.9%)略高于夏季(57.4%),而夏季SOC/OC(52.5%)略高于秋季(49.0%).夏季和秋季SOC/OC都低于WSOC/OC,说明部分水溶性有机碳是一次源.WSOC和SOC相关性强,进一步验证了大部分SOC具有水溶性.碳质组分之间的关系及主成分分析表明,采样期间燃煤和机动车尾气排放是碳质组分的两个主要来源.后向轨迹分析表明,采样点PM_(2.5)和碳质组分主要受当地排放源和短距离传输的影响,长距离传输贡献较小.

To better understand the characterization and sources of carbonaceous components,a total of 60 fine particle（PM2.5）samples were collected in Changzhou during summer（July to August） and fall（October to November） of 2016.The average mass concentrations of PM（2.5）,organic carbon（OC）,and elemental carbon（EC） during this study period were observed to be 73.0,14.3 and 3.3 μg·m^-3 in summer and 84.2,13.2,and 3.5 μg·m^-3 in fall,respectively.The average mass fraction of carbonaceous aerosols（OC ＋ EC） in the PM（2.5） measurement was estimated to be 24.3% in summer and 20.7% in fall.Eight carbonaceous fractions,resolved by following the IMPROVE-A thermal/optical reflectance protocol,showed strong correlation（r 0.92） between OC2,OC3,OC4 and EC1 and close correlations between EC2 and EC3（r 〉0.65）,indicating probable similar contributors.OC and EC were moderately correlated,suggesting complex contributions to carbonaceous aerosol.The water soluble organic carbon（WSOC）to OC ratio（WSOC/OC） in the fall（60.9%） was slightly higher than that in the summer（57.4%）,while secondary organic carbon（SOC） to OC ratio（SOC/OC） was lower in the fall（49.0%） compared with the summer（52.5%）.The SOC/OC ratio was lower than the WSOC/OC for both seasons,suggesting that part of WSOC component originates from primary emissions.The significant correlation of WSOC and SOC confirms that most SOC is water soluble.Relationships between each carbonaceous species and the principal component analysis indicate that vehicle emissions and coal combustion are the two main emission sources of carbonaceous aerosols from the observation period.Back trajectory analysis was used to indicate that carbonaceous components at sampling site are mainly affected by local emission sources and short distance transport,whereas the contribution of long-distance transmission is small.