中国沿海地区大气污染特征及其聚类分析

为识别我国沿海地区的大气污染分布特征，基于2015—2016年我国沿海12个省（自治区、直辖市）的115个地级以上城市ρ（PM_2.5）、ρ（PM₁₀）、ρ（NO₂）、ρ（O₃）、ρ（CO）和ρ（SO₂）监测数据，在分析其时空分布特征的基础上，结合主成分分析和AIC（改进赤池信息准则）开展我国沿海地区大气污染聚类分析研究.结果表明:我国沿海地区颗粒物污染严重，其中70%和54%的城市未达到GB 3095—2012《环境空气质量标准》中ρ（PM_2.5）和ρ（PM₁₀）二级标准，ρ（PM_2.5）在空间上以浙江省金华市为界呈“北高南低”、金华市以北地区“西高东低”的分布特征；环渤海带及长三角地区ρ（O₃）处于相对较高水平，山东省中部ρ（SO₂）突出，最高值达71.3 μg/m3.根据6种大气污染物监测值，可将115个地级以上城市聚为3类:类Ⅰ包括河北省南部和山东省西部在内的21个城市，空间分布连续且相对集中，受本地源和扩散条件的影响，各项大气污染物质量浓度均处于较高水平；类Ⅱ包括辽宁省、山东省东部和长三角等地区的42个城市，各项大气污染物质量浓度较类Ⅰ有所降低，ρ（PM_2.5）降低（比类Ⅰ低34.2%）明显，更多表现为受工业和散煤燃烧影响的SO₂污染，和受海运船舶和陆路交通源影响的NO₂污染；类Ⅲ包括福建省、广东省和广西壮族自治区沿海一带的52个城市，大气污染物质量浓度相对较低，空气质量较优，受季风和外来源影响的秋季O₃污染特征明显.3类城市ρ（O₃）平均值相近但季节性变化有所差异，类Ⅰ和类Ⅱ ρ（O₃）峰值均出现在6月，类Ⅰ ρ（O₃）季节性差异更为显著，类Ⅲ峰值出现在10月，全年变幅相对较小.研究显示，我国沿海地区山东省西部、江苏省北部与京津冀地区南部呈较为相似的污染特征，广西壮族自治区柳州市与周边城市呈不同聚类特征，ρ（PM）和ρ（SO₂）相对较高，为大气污染热点. 

Characteristics and Cluster Analysis of Air Pollution in Coastal Areas of China

To identify the distribution characteristics of air pollution in the coastal areas of China, this paper analyzed the spatial-temporal variation of six criteria air pollutants (PM_2.5, PM₁₀, NO₂, O₃, CO and SO₂) based on the observations from 115 cities in the coastal provinces of China during 2015-2016. Cluster analysis coupled with principal component analysis (PCA) and improved Akaike information criterion (AIC) were applied to explore the regional pollution situations. The results showed that the coastal areas of China was seriously polluted by particulate matter (PM), with 70% cities for PM_2.5 and 54% cities for PM₁₀ fell below the national secondary standard, according to the National Ambient Air Quality Standard (GB 3095-2012). For ρ(PM_2.5), it demonstrated obvious spatial variations between the south and north, with Jinhua City in Zhejiang Province as a demarcation belt. The heavily polluted areas appeared in northern areas in which it showed an increasing trend from east to west. The O₃ concentrations around the Bohai Sea and Yangtze River Delta were at relatively high level, while the highest SO₂ concentration (71.3 μg/m3) was located in middle Shandong Province. Furthermore, according to the observed six criteria air pollutants, all the 115 cities could be clustered into 3 categories. Cluster Ⅰ included 21 cities in south Hebei and west Shandong provinces. The spatial distribution for air pollutants were continuous and relatively centralized with the highest pollutant concentrations and the worst air qualities due to the local emission and diffusion conditions. Cluster Ⅱ included 42 cities which were mainly distributed in Liaoning province and the Yangtze River Delta. It showed medium air qualities with considerable SO₂ and NO₂ pollution due to coal burning, plants emission as well as vehicle and shipping emission. The PM_2.5 concentration in Cluster Ⅱ was 34.2% lower that of Cluster Ⅰ. Cluster Ⅲ included 52 cities with the best air quality and were mainly distributed in the southeast coastal areas of China with O₃ pollution due to monsoon and outside sources. Moreover, the average O₃ concentrations among the three clusters were similar but the seasonal variations were different. Specifically, Clusters Ⅰ and Ⅱ were characterized with the apparent seasonal variation and the highest values appeared in June. For Cluster Ⅲ, there was no obvious seasonal variations with the highest values in October. In particular, western Shandong and northern Jiangsu provinces showed similar pollution characteristics to southern Beijing-Tianjin-Hebei region and Liuzhou was one of the air pollution hot spots in the Guangxi Zhuang Autonomous Region.