基于Ward系统聚类的京津冀城市群空气质量时空变化特征与成因分析

京津冀城市群是中国空气污染最严重的区域之一,探明该地区空气质量的时空变化特征和影响因素对空气污染防治具有重要意义。利用2014—2018年空气实时监测数据,运用系统聚类与空间分析方法,研究京津冀城市群空气质量的时空变化特征和关键影响因素,结果表明:2014—2018年京津冀城市群空气质量改善趋势明显,SO₂、PM_2.5、PM₁₀与CO浓度均有显著下降,O₃浓度逐年升高;以PM_2.5、PM₁₀、NO₂与O₃四项污染物浓度指标为依据,可将区域空气质量状况分为“低-低-低-低”(Ⅰ类),“中低-中低-高-中低”(Ⅱ类),“中高-中高-中低-高”(Ⅲ类)与“高-高-中高-中高”(Ⅳ类)4个区域,区间城市的地理点具有空间上的连续性,区内城市则具有空间上的聚集性;空气质量指数(AQI)呈“秋冬高,春夏低”的变化特点,5—9月O3污染突出,10月至次年4月颗粒物污染突出,四类分区内的特征污染物和变化规律各异;污染“热点”始终保持在保定西部-石家庄-邢台-邯郸一带,区域春夏季AQI的差异表现为东西向,秋冬季则表现为南北向;政策影响对污染物减排作用明显,是整个地区空气质量改善的根本原因。太阳辐射、空气湿度、季风等气象因素是张家口与承德夏季臭氧污染的关键因子,污染物排放变化是第Ⅱ、Ⅲ、Ⅳ类城市空气质量改善的主要原因,风速,降雨等气象因子具有局部调节作用。在微观区域分析中,第二产业比重对PM_2.5和O₃的影响以北京-廊坊-天津为核心由内而外逐渐减小,汽车拥有量的影响逆向增加。

Spatial-temporal Variation Characteristics of Air Quality and Its InfluencingFactors of the Beijing-Tianjin-Hebei Urban Agglomeration Based on WardHierarchical Clustering

Air pollution is one of the most serious environmental problems in China,especially for Beijing-Tianjin-Hebei(Jing-Jin-Ji)urban agglomeration.It is of great significance for air pollution prevention to study the temporal-spatial characteristics of air quality and its influencing factors.This paper applies the Ward hierarchical cluster analysis and spatial analysis to study the spatial-temporal variation characteristics of air quality and its influencing factors in Jing-Jin-Ji urban agglomeration based on the air real-time monitoring data from 2014 to 2018.The results are as follows:(1)The air quality of Jing-Jin-Ji urban agglomeration was improving from 2014 to 2018.The concentration of SO₂,PM_2.5,PM₁₀ and CO decreased,while the concentration of O₃ was on the rise.(2)The region was divided into four typical pollution classes based on concentration indexes of PM_2.5,PM₁₀,NO₂ and O₃,which were“lowlow-low-low”(Class I),“medium low-medium low-high-medium low”(Class II),“medium high-medium high-medium low-high”(Class III)and“high-high-medium high-medium high”(Class IV).The geographical points between regions presented spatial continuity,while the cities in the region showed clustering.(3)The air quality index(AQI)was on a high level in autumn and winter,and it was low in spring and summer.Ozone pollution was prominent from May to September,while particle pollution was outstanding from October to the following April.There were different typical pollutants with characteristics depending on the class.(4)The AQI annual average increased from northeast to southwest(Class I-Class IV).West Baoding,Shijiazhuang,Xingtai and Handan composed a serious pollution belt.The variation of the AQI in spring and summer was to the east-west direction while it turned to the south-north direction in autumn and winter.And(5)the effect of policies on pollutant emission reduction was obvious,which was the fundamental reason for the improvement of air quality in the whole region.Solar radiation,air humidity,monsoon and other meteorological factors were the key factors of ozone pollution in summer in Zhangjiakou and Chengde.The change of pollutant emission was the main reason for the change of air quality in Classes II,III and IV,and the meteorological factors,such as wind speed and rain,were of regulation effect.In micro-analysis,with Beijing-Langfang-Tianjin as the core,the influence of the proportion of the second industry on PM_2.5 and O₃ gradually decreased from the inside to the outside,while the impact of automobile ownership increased in reverse.