山东省环境空气中PM2.5与O3的复合污染特征与时空变化趋势

山东省PM_2.5-O₃复合污染特征突出，空间差异性明显，本文基于2016—2020年国控和省控环境空气自动监测站监测数据以及同期各气象代表站气象监测数据，分析PM_2.5和O₃时空分布的变化特征，初步探究其与气象因子及前体物的关系. 结果表明:①2016—2020年山东省空气质量逐步改善，优良天数比例上升了7.1%，重污染天数比例下降了3.5%. 除O₃年评价值上升9.6%以外，SO₂、PM₁₀、PM_2.5、CO和NO₂的浓度均下降，降幅依次为61.3%、29.8%、28.6%、26.3%和11.4%. 各市PM_2.5年评价值均下降(范围为18.4%~34.9%)；除德州市外，其他15市O₃年评价值均上升，滨州市的升幅(30.8%)最大. 1月PM_2.5平均浓度最高，呈现先下降后上升的年变化趋势，6月O₃平均浓度最高，且逐年上升. ②山东省PM_2.5和O₃均呈现内陆地区高于沿海地区的分布特征，PM_2.5浓度在西部内陆地区较高，O₃浓度在中北部内陆地区较高，PM_2.5-O₃复合污染特征在中西部地区较明显. 统计期间共计出现PM_2.5-O₃复合污染日224 d，分布在2—11月，出现天数逐年减少. ③为探究PM_2.5-O₃复合污染的影响因素及气象特征，进行相关性分析及气象因子阈值筛查，结果表明，PM_2.5日均浓度和O₃_8 h (臭氧日最大8小时滑动平均值)与其主要前体物和气象因子均呈现相反的相关关系，且对不同因子的响应有一定区域性差异. 当气温为14.9~24.1 ℃、相对湿度为55.5%~75.1%、风速为0.6~2.9 m/s、气压为992.8~1 018.8 hPa时PM_2.5-O₃复合污染易于发生，该条件下大部分城市的气温、相对湿度和气压平均值介于PM_2.5和O₃污染单独发生时的对应因子平均值，但平均风速小于PM_2.5和O₃污染单独发生的平均风速. 研究显示，“十三五”期间山东省PM_2.5浓度波动下降，O₃浓度波动上升，二者的协同关系日趋明显，气象因素对PM_2.5和O₃的生成和累积有一定影响. 

Characteristics and Spatiotemporal Variation of PM2.5 and O3 in Shandong Province

The composite characteristics of PM_2.5-O₃ in Shandong Province were relatively prominent and also showed obvious spatial differences. To study characteristics of co-pollution of surface O₃ and PM_2.5 in Shandong province, the spatial distribution of the PM_2.5 and O₃ concentration was analyzed, and the relationship between O₃ and PM_2.5, meteorological parameters and their precursors was explored based on the monitoring data of national and provincial ambient air quality monitoring sites and meteorological sites from 2016 to 2020. The results indicated that: (1) During 2016-2020, the air quality in Shandong Province improved gradually, the number of days with excellent and good air quality increased by 7.1%, and heavily polluted days decreased by 3.5%. Except for the 90th percentile of the maximum daily 8-hour average of the O₃ concentration (O_{3 MDA8} 90th), which increased by 9.6%, the concentration of SO₂, PM₁₀, PM_2.5, CO and NO₂ decreased by 61.3%, 29.8%, 28.6%, 26.3% and 11.4%, respectively. The annual average PM_2.5 values of all cities in Shandong Province decreased by 18.4% to 34.9%. The O_{3 MDA8} 90th increased in all the cities except for Dezhou City. The largest increasing ratio of O_{3 MDA8} 90th was 30.8% in Binzhou City. The highest average PM_2.5 concentration occurred in January, while the highest average O₃ concentration occurred in June. The PM_2.5 concentration in January decreased and then increased from 2016 to 2020, while the O₃ concentration in June increased from 2016 to 2020. (2) The PM_2.5 and O₃ concentration in inland cities was higher than those in coastal cities. PM_2.5 concentration in the western inland area was higher, and O₃ concentration in central and northern inland area was higher. The synergistic pollution characteristics of PM_2.5 and O₃ were obvious in the central and western Shandong Province. During the whole study period, there were 224 days of the synergistic pollution of PM_2.5 and O₃, which mainly occurred from February to November. The number of PM_2.5 and O₃ synergistic pollution days decreased year by year. (3) The correlations between PM_2.5 or O₃ concentration and meteorological factors, and the thresholds of meteorological factors during PM_2.5, O₃ or PM_2.5-O₃ composite pollutant days were also studied. The results showed that the daily average PM_2.5 and O₃_8 h concentrations had negative correlations with their precursors and meteorological parameters. Moreover, there were spatial differences in the correlations between PM_2.5 and O₃, their precursors and meteorological parameters. The statistical results showed that PM_2.5-O₃ complex pollution was favorable to occur when the atmospheric temperature, relative humidity, wind speed, and atmospheric pressure were 14.9-24.1 °C, 55.5%-75.1%, 0.6-2.9 m/s, and 992.8-1018.8 hPa, respectively. In most cities of Shandong Province, the average values of atmospheric temperature, relative humidity and atmospheric pressure during the synergistic pollution of PM_2.5 and O₃ were between those during the PM_2.5 pollution and those during the O₃ pollution. But the average wind speed during the synergistic pollution of PM_2.5 and O₃ was lower than those during the PM_2.5 pollution and during the O₃ pollution. In summary, the study showed that the PM_2.5 concentration decreased overall, while O₃ concentration increased, and the synergistic changes of PM_2.5 and O₃ became more obvious during the ‘13th Five-Year Plan’ period. Meteorological factors played a role in the formation and accumulation of PM_2.5 and O₃.