南京近郊主要大气污染物的观测分析研究

Observation of main air pollutants at a suburban site in Nanjing

2007年10月至2008年9月在南京的一个近郊站点(32°03′N,118°78′E)对可吸入颗粒物(PM10)、臭氧(O3)、二氧化硫(SO2)、一氧化碳(CO)、氮氧化物(NOx)和氨气(NH3)等6种大气中的主要污染物进行了为期一年的连续监测.本文利用统计方法研究了这些污染物不同时间尺度(小时、日、周、月)的浓度变化特征和相互关系,并利用后向轨迹和聚类分析方法研究了不同季节到达该测站的气团来源及化学特征.结果表明,PM10、O3、SO2、CO、NOX和NH3的年均浓度和标准差分别为0.14±0.08 mg/m3(、18.52±14.05)×10-9(、21.14±15.96)×10-9(、1.08±0.98)×10-6(、24.57±24.65)×10-9(、24.33±15.73)×10-9.O3浓度表现出明显的白天高、夜间低的日变化特征,SO2和PM10一般在早上9、10点钟达到一天中的最大值,NOX呈双峰结构;O3春季浓度高,2008年2月出现峰值,可能与当年冬季持续降雪有关.NOX、NH3浓度呈现秋冬季节低、春季高的特点,而PM10和SO2则相反;O3周末浓度低,工作日浓度高,SO2和O3前体物NOX、CO在周末的浓度高于工作日.研究还发现,O3和NOX、CO都呈现一定的负相关,相关系数分别为-0.36和-0.42.后向轨迹分析显示近距离输送对该测站大气污染物浓度的季节变化贡献显著,远距离输送也起了一定的作用.夏季受东南风影响,来自南方海上的气团较干净,O3、SO2和CO的浓度分别为(11.96±9.22)×10-9(、5.60±4.10)×10-9和(0.45±0.26)×10-6;冬季测站受来自北方的大陆性气团控制,浓度较高,局地源贡献明显,PM10、SO2、CO、NOX和NH3的浓度分别为0.19±0.10 mg/m3,(32.31±21.28)×10-9,(1.00±0.93)×10-6,(31.41±32.29)×10-9和(29.38±17.18)×10-9,均高于其他气团.

Continuous measurements of respirable particulate matter （PM10）, ozone （03）, sulfur dioxide （SO2）, carbon monoxide （CO）, nitrogen oxides （NOx）and ammonia （NH3） at a suburban site（32°03＇N, 118°78＇E） in Nanjing were conducted during the period from October 2007 to September 2008. The surface concentration variations on different time scales（hourly, daily, weekly, monthly） of air pollutants and their relationship were studied through statistical method. Backward trajectory and cluster analysis were used to isolate air masses reaching the site with different chemical characteristics. Investigations show that the annual mean surface concentration and standard deviation of PM10, O3, SO2, CO, NOx and NH3 are 0.14 ± 0.08 mg/ma , （ 18.52 ± 14.05） ）× 10-9 , （21. 14±15.96） ）× 10-9 , （1.08±0.98） × 10 6, （24.57±24.65） × 10 9, （24. 33± 15.73） × 10-9 , respectively. A clear diurnal pattern was observed for O3 concentration with maximum in the afternoon and low level at night. SO2 and PM10 concentrations show peaks at 9 or 10 am in the morning, and NOx concentration exhibits two peaks. O3 is high in spring, with peaks in Feb. , 2008, which may be associated with the continuous snow storm in that period. NOx and NH3 concentrations are low in autumn and winter and high in spring, while PM10 and SO2 concentrations are high in autumn and winter and low in spring. In addition, Oalevel is lower at weekends compared to weekdays, while SO2, CO, NOx concentrations are higher at weekends than those on weekdays. In addition, both NOx and CO have a negative correlation with O3 , their correlation coefficients are --0. 36 and --0.42 separately. The backward trajectory cluster analyses indicated that local sources make a great contribution to the air pollutants arriving at the site, but long range transport also plays an important role in the seasonal variations of the air pollutants. As affected by the Southeast wind in summer, the maritime air masses were relatively clean with O3, SO2 and CO concentrations of （11.96±9.22）×10 9,（5.60±4.10）×10-9 and （0.45±0.26）×10 6 while the cold northern air masses with high pollutant level dominate in winter. The local sources have significant impact in winter. The concentrations of PM10,SO2,CO,NOx and NHa in local air mass are 0. 19±0.10 mg/m^2,（32.31±21.28）×10 9,（1.00±0.93）× 10 -9 , （31.41 ±32.29）× 10 9 and （29.38±17.18）× 10-9 , which are higher compared to other kind of air masses.