北京地区PM_(2.5)的成分特征及来源分析

Componential Characteristics and Sources Identification of PM_(2.5) in Beijing

选用2003--2004年初PM25连续观测资料，统计分析了北京地区PM25的特征、PM25与PM10以及PM25与地面气象要素的相互关系。结果表明：四季中夏季PM25浓度最低，冬、春两季浓度较高。PM25与PM10比值平均为0．55，非采暖期两者比值为0．52，采暖期两者比值为0．62；夏季该比值主要分布在0．3～0．6之间，春、秋两季该比值分布在0．3～0．8之间，冬季采暖期该比值分布在0．4～0．9之间。PM2，与PM10比值日变化与气象条件日变化、人们日常生活习惯密切相关，沙尘天气和交通运输高峰期扬起地面粗颗粒物会导致PM2，在PM10中的比例下降，而冬季取暖以及夏季光化学反应则会引起PM25的比例升高。PM25的浓度与地面气象要素中本站气压、相对湿度和风速有很好的的相关性，与气温的相关性较差。SO4^2-，NO3^-和NH4^＋为北京地区PM25中主要离子。PMF源解析方法确定了北京地区5类细粒子污染源，分别是：土壤尘、煤燃烧、交通运输、海洋气溶胶以及钢铁工业。

Statistic analysis is made of the characters of the mass concentrations and chemical compositions of PM2.5 in Beijing, based on the observations during the period of 2003 to 2004. It is found that the mean concentration of PM2.5 shows the lowest value in summer, while it reaches the maximum of year in winter and spring. Moreover, the daily average mass concentration of PM2.5 in summer is 71 μg/m^3, which is lower than that in other seasons of about 110 μg/m^3. The yearly average mass concentration of PM2.5 is 100 μg/m^3, which is much higher than the U S Air Quality Standard for yearly average mass concentration of PM2.5 of 15 μg/m^3. Then, the relationship of PM2.5 and PM10 is discussed. The mean ratio of PM2.5 to PM10 is 0.55 for the whole year, which is close to the values in previous research for other cities including Guangzhou, Wuhan, Chongqing and Lanzhou in China. In addition, the mean ratio of PM2.5 to PM10 is 0.62 and 0.52 for the heating and non-heating season respectively. It shows a slightly high trend in the heating period. Seasonal characteristics of the ratio of PM2.5 to PM10 is 0.3--0.6 in summer, 0.3--0.8 in spring and autumn, and 0.4--0.9 in winter. The results indicate that diurnal ratio of PM2.5 to PM10 responds to the meteorological conditions and the anthropogenic activities. Sand-dust weather and daily traffic lead to the increase in concentration of coarse particles more rapidly than that of fine particles in atmosphere. As a result, the ratio of PM2.5 to PM10 decreases. On the other hand, the house heating in winter and the photochemical reaction in summer cause the increase in the ratio of PM2.5 to PM10 as well. Furthermore, the analysis to meteorological factors reveals that the change of the concentration of PM2.5 is well related to pressure, relative humidity, and wind speed. In addition to the positive correlation with humidity, the mass concentration of PM2.5 is negatively correlated with wind and pressure except in summer. Finally, the sources of PM2.5 are analyzed by using the method of positive matrix factorization. It is found that SO4^2-, NO3^- and NH4^＋ are the primary water-soluble ions in PM2.5 in Beijing. Moreover, five sources of PM2.5 in Beijing are identified. They are soil dust, coal combustion, traffic, sea-salt aerosol and steel production. Compared with the results of previous research in sources identification of aerosol in Beijing, some conclusions are made. Firstly, soil dust and coal combustion have been the primary sources since 1980s, while the contribution of traffic emission to fine particles has grown gradually from 1983 to 2001. Secondly, the effects of a number of sources including coal combustion, sea-salt aerosol, biofuel combustion and second aerosol, on PM2.5 vary with seasons. Thirdly, the process of transportation affects the composition of PM2.5 distinctly, and the characteristic element of PM2.5 from special sources related with the wind direction closely. Besides, the results of sources identification to PM2.5 in Beijing area are different in different sites and periods. As a result, selecting representative sites and observing period for the study is very important.