衡水市大气污染成因研究及治理经验

衡水市作为"2+26"城市中典型的低GDP、高污染城市，其空气质量排名常年处于74个重点城市的后10位.自大气重污染成因与治理攻关项目工作开展以来，衡水市开展了大量污染成因研究及污染治理工作，已取得了较为明显的大气污染治理成效.从空气质量变化、排放源、污染物来源解析及气象条件与排放贡献等方面，梳理了衡水市大气污染成因研究及治理经验.结果表明:①衡水市的空气质量得到较大改善，PM₁₀和PM_2.5治理成效明显.2018年衡水市ρ（PM₁₀）和ρ（PM_2.5）年均值比2017年分别下降了25.12%和19.73%，比2013年分别下降了54.84%和51.22%，但O₃污染形势逐渐严峻，以O₃为首要污染物的天数由55 d（2013年）增至125 d（2018年）.②相比于2016年，衡水市2017年SO₂、NO_x、CO、PM₁₀、PM_2.5、BC、OC、VOC的排放总量均大幅下降.③2013-2018年导致衡水市PM_2.5下降的因素中，气象因素占8.0%，排放源因素占92.0%，说明衡水市通过减排措施改善空气质量的效果较为显著.④硝酸盐已经取代硫酸盐成为秋冬季颗粒物二次转化中最重要、占比最高的成分.研究显示，衡水市高ρ（PM_2.5）主要以本地排放和临近地区输送为主，为有效控制衡水市PM_2.5污染的发生与发展，应采取本地排放控制与"2+26"城市联防联控相结合的方案. 

Causal Analysis of Air Pollution and Mitigation Experience in Hengshui City

Hengshui City is a typical low-GDP and high-pollution city in the '2+26' cities, and the AQI of Hengshui City ranks in the bottom ten in 74 cities. Since a National Research Project for Tracking Key Problems Air Pollution Control, a broader research in Hengshui City, which analyses the causes and solution of the local atmospheric pollution, has been carried out and obviously improved the air quality. The paper sorts out the causal factors and management experiences in Hengshui City based on the factors such as variation of air quality, emission sources, source apportionment and the contribution from meteorological conditions and source emissions.The conclusions are as follows:(1)The air quality has been improved dramatically since the implementation of the key project. In 2018, the annual average ρ(PM₁₀) and ρ(PM_2.5)in Hengshui City decreased by 25.12% and 19.73% compared with 2017 and by 54.84% and 51.22% compared with 2013, respectively. However, O₃ pollution became worse, and the major pollutant days increased from 55 days in 2013 to 125 days in 2018. (2) Compared with 2016, the emissions of SO₂, NO_x, CO, PM₁₀, PM_2.5, BC, OC and VOCs decreased substantially in 2017. (3) Among all the factor causing the decrease in PM_2.5 concentration during 2013-2018, meteorological condition accounted for 8.0% and the emission reduction accounted for 92.0%, which indicates that the emission reduction measures played a significant role in improving the air quality in Hengshui City. (4) Nitrate replaced sulfate as the most important and highest proportion of secondary particles in autumn and winter. The research shows that the high PM_2.5 concentration in Hengshui City mainly originates from the local emission and the transportation from adjacent areas. Therefore, a joint effort of local emission reduction and regional prevention policy in all '2+26' cities should be taken to effectively control the occurrence and deterioration of aerosol pollution in Hengshui City.