京津冀及周边地区采暖季PM2.5化学组分变化特征

利用京津冀及周边地区大气污染综合立体监测网，在京津冀大气污染传输通道城市（“2+26”城市）开展了PM_2.5及其化学组分长期连续观测，并对数据进行深入分析.结果表明:①2017年、2018年和2019年采暖季“2+26”城市PM_2.5浓度平均值分别为（84±62）（95±63）和（80±61）μg/m3，达到了京津冀及周边地区2019—2020年秋冬季PM_2.5平均浓度同比下降4%的目标；与PM_2.5浓度变化相似，其主要化学组分——有机物（OM）浓度最大值出现在2018年采暖季，但二次无机盐（硝酸盐、硫酸盐和铵盐）浓度呈逐年上升趋势，而元素碳、氯盐、地壳物质和微量元素浓度均呈逐年下降趋势.②OM、硝酸盐、硫酸盐、铵盐、地壳物质、元素碳、氯盐和微量元素浓度空间分布存在明显差异.受污染物排放、气象条件以及地形因素的共同影响，PM_2.5及其化学组分浓度高值区主要出现在太行山传输通道城市（保定市、石家庄市、邢台市、邯郸市、安阳市和新乡市）.③不同空气质量状况下，“2+26”城市PM_2.5化学组分浓度年际变化相似，即随空气污染的加重，硝酸盐、硫酸盐和铵盐占PM_2.5的比例均上升，而OM占比下降.研究显示，采暖季“2+26”城市空气质量总体得到改善，但需进一步加强对PM_2.5中二次组分的科学管控. 

Characteristics of Chemical Composition of PM2.5 in Beijing-Tianjin-Hebei and Its Surrounding Areas During the Heating Period

Based on the comprehensive three-dimensional observation network in the Beijing-Tianjin-Hebei and its surrounding areas ('2+26' cities), continuous observation and in-depth analysis of PM_2.5 and its chemical components were carried out. The results indicated that: (1) During the heating period in 2017, 2018 and 2019, the average concentration of PM_2.5 was (84±62), (95±63) and (80±61)μg/m3, respectively, which reached the goal of a 4% reduction in the average concentration of PM_2.5 in the Beijing-Tianjin-Hebei and its surrounding areas from 2019 to 2020. As the main PM_2.5 chemical composition, the variation of organic matter (OM) was similar to that of PM_2.5 in the heating period with the highest average value observed during the heating period of 2018-2019. The concentrations of nitrate, sulfate and ammonia increased year by year, while the concentrations of elemental carbon, chloride, crustal and trace elements decreased accordingly. (2) Obvious spatial difference was observed in OM, NO₃-, SO₄2-, NH₄+, crustal matter, elemental carbon, Cl- and trace elements. Affected by source emissions, meteorological conditions and topography, the high-value region of PM_2.5 and its chemical components mainly appeared in the cities along the Taihang Mountain transport pathway, including Baoding, Shijiazhuang, Xingtai, Handan, Anyang and Xinxiang. (3) Under different air quality levels, similar interannual variations were observed in the concentrations and ratios of PM_2.5 chemical species during the heating periods of 2017-2019, i.e., the ratios of (NO₃-, SO₄2- and NH₄+)/PM_2.5 increased but the ratios of OM/PM_2.5 decreased with air quality degradation. The results showed that the air quality during the heating periods improved on the whole, but the scientific strategies of controlling secondary inorganic ions were strictly executed.