2017年上半年北京市及周边地区空气质量特征分析

依托北京市、廊坊市和保定市高密度的地面空气质量监测、气象要素监测以及PM_2.5化学组分监测和后向轨迹分析等手段,对2017年上半年三地的空气质量进行分析。研究发现：三地中北京市空气质量较好,保定市较差。分污染物来看,保定市SO₂浓度水平明显高于廊坊市和北京市,颗粒物PM₁₀和PM_2.5也呈现保定市最高、北京市最低的规律。从污染物日变化来看,CO、SO₂、NO₂、PM₁₀和PM_2.5呈双峰型分布,O₃呈单峰型分布。从区域整体分布规律来看,PM_2.5和SO₂呈现明显的"南高北低"特征。PM_2.5化学组分分析结果表明：1—4月燃煤对该区域空气质量的影响较大,5—6月机动车排放的影响更为凸显。后向轨迹分析结果表明：在2017年上半年到达北京市的气流中有24%来自于北京市南部,且这些气流多为低空传输,表明区域传输对于北京市空气质量具有一定的影响。

Analysis of Air Quality During the First Half of 2017 in Beijing and the Surrounding Region

This study analyzed the air quality of Beijing,Langfang and Baoding in the first half of 2017 based on the backward trajectory analysis and high-density monitoring data of air pollutant,meteorological elements and chemical composition of PM_2.5. The results showed that the air quality of Beijing was the best among these three cities,while that of Baoding was the worst. The monthly average concentration of SO₂ in Baoding was significantly higher,while the spatial distribution of PM₁₀ and PM_2.5 concentrations was similar to SO₂ concentrations. From the perspective of the diurnal variation,CO,SO₂,NO₂,PM₁₀ and PM_2.5 showed a bimodal distribution pattern while O₃ had a single-peak distribution pattern. From the perspective of spatial distribution,PM_2.5 and SO₂ concentrations were both higher in the south part and lower in the north part. The analysis of PM_2.5 chemical composition showed that coal burning significantly influenced the air quality in this region from January to April,while vehicle emissions had more significant impacts on the air quality from May to June. The results of backward trajectory analysis showed that 24% air masses into Beijing came from the south of Beijing in the first half of 2017,most of which were transmitted at the low altitude and could easily transport air pollutants into Beijing. These results showed that the regional transmission had some effects on the air quality of Beijing.