针对日益严重的空气污染问题,采用2015—2016年全国334个城市空气质量监测数据,利用全域空间自相关、自然正交函数和空间描述性统计的方法来探索城市空气质量指数的时空动态变化特征。结果发现：①2016年较2015年全国AQI均值下降5.4%,其中夏季AQI值降幅最大,同比下降了9.44%,而春季AQI值降幅最小,同比下降了1.55%。分月来看,AQI呈现出U型分布,且6~8月为U型谷底。逐日来看,秋季和冬季的日均AQI波动幅度最大,2016年全国日均AQI达优良率较2015年上升4.14%。②2016年空气污染的区域范围相比2015年有缩小趋势。其中,京津冀城市群、山东半岛城市群和河南省以北地区围成的重污染区域呈现明显的收缩态势。京津冀城市群、山东半岛城市群和长三角城市群等空气质量优良率增长较快,而咸阳、渭南和阳泉等城市空气质量优良率呈下降态势。自然正交函数结果显示：新疆西部和冀鲁豫为高污染聚集的中心区域,而AQI低值区域则集中在云南、四川、贵州和海南的大部分地区。③2016年空气污染集聚程度高于2015年,京津冀地区和新疆西部地区仍然是空气污染的主要聚集区。
China has been suffering from the issue of the serious air pollution recently. Based on a data-set of air quality index of 334 cities in China from 2015 to 2016, this paper employs global spatial autocorrelation analysis, empirical orthogonal function and spatial descriptive statistics methods to investigate the spatio-temporal variation of air quality index of 334 cities. The findings are the following. 1) The yearly average value of AQI in 2016 was reduced by 5.4% from the benchmark in 2015. Moreover, the excellence rate in 2016 was improved by 4.14% from the benchmark in 2015. From the perspective of the quarterly time scale, AQI of 2016’s summer declined greatly, specifically by 9.44% from the benchmark in 2015’s summer while AQI of 2016’s winter declined slightly, specifically by 1.55% from the benchmark in 2015’s winter. Overall, AQI presented a U-shaped curve at the monthly time scale. Moreover, AQI values reached the nadir from June to August. The average values of daily AQI had the biggest variations in autumn and in winter. What's more, the excellence rate of the average value of AQI was improved by 4.14% compared with 2015. 2) The highly-polluted area in 2016 shrunk remarkably compared with 2015. Specifically, Beijing-Tianjin-Hebei Urban Agglomeration, Shandong Peninsula Urban Agglomeration and the northern Henan are traditionally air-polluted regions. The highly-polluted area of these regions became smaller compared with the year of 2015. In addition, the excellence rate of air quality of Beijing-Tianjin-Hebei Urban Agglomeration, Shandong Peninsula Urban Agglomeration and Yangtze River Delta Urban Agglomeration increased sharply during the sample period. On the other hand, the excellence rate of air quality of Xianyang, Weinan and Yangquan showed decreasing trends. The results of empirical orthogonal function indicated that from the monthly time scale the western Xinjiang, Hebei, Shandong and Henan were still highly polluted regions, while the most areas of Yunnan, Sichuan, Guizhou and Hainan showed lower AQI values, implying that these cities had good air quality conditions. 3) In 2016, air quality index of cities showed a higher clustering coefficient than that in 2015. Still Beijing-Tianjin-Hebei Urban Agglomeration and the western Xinjiang are highly-air-polluted regions.
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