2016年11—12月北京及周边重污染过程PM2.5特征

该文对2016年11—12月北京及周边地区不同站点重污染期间PM_2.5质量浓度变化特征进行分析，并结合地面和探空气象要素及化学组分等对重污染成因进行深入探讨，比较了其中两次持续3 d及以上重污染过程的异同。结果表明:重污染期间北京及周边地区PM_2.5质量浓度较高，北京上甸子站、顺义站、朝阳站的PM_2.5质量浓度分别为73.1，130.8，226.0 μg·m-3，河北保定站和石家庄站分别为357.8 μg·m-3和346.9 μg·m-3。12月17—21日重污染过程比11月3—5日持续时间更长且PM_2.5质量浓度更高。通过对11—12月所有重污染过程分析发现，北京颗粒物重污染发生的主要气象条件是静稳天气。在排放源相对稳定情况下，逆温层的结构、演变和持续时间决定了重污染的程度，其中污染持续时间和污染期间的主导逆温层类型演变对重污染程度有较好的指示作用。较低的水平风速、逆温层的持续出现及更多的燃煤和机动车尾气排放是12月17—21日污染偏重的原因。

Characteristics of PM2.5 in Heavy Pollution Events in Beijing and Surrounding Areas from November to December in 2016

PM_2.5 and PM₁₀ mass as well as meteorological data at six stations in Beijing and Hebei Province are analyzed to investigate characteristics of heavy pollution processes from November to December of 2016. Results show that PM_2.5 concentrations are 73.1, 130.8 μg·m-3 and 226.0 μg·m-3 at Shangdianzi, Shunyi and Chaoyang stations in Beijing during the heavy pollution, which are lower than those measured at Baoding and Shijiazhuang stations in Hebei (357.8 μg·m-3 and 346.9 μg·m-3, respectively). The average concentration of PM_2.5 for the heavy haze days is 3-4 times of that in clean days at all six stations, with the haze accompanied by calm wind, high humidity, and other adverse weather conditions. Observations indicate most pollution cases last longer in Hebei than those in Beijing, which is probably caused by intensified emissions from industry in Shijiazhuang. In addition, the sulfur dioxide, nitrogen oxides and particulate matter discharged from Shijiazhuang and Baoding are blocked by the Taihang Mountains, which make pollutants easy to accumulate in this area.The daily average air quality index (AQI) during heavy pollution events has a complex relationship with the type, strength, duration and thickness of the inversion layer. Meanwhile, it has good consistency with the duration of the inversion both before and after the heating period in Beijing. The analysis of sounding data indicates that the atmospheric boundary layer also plays an important role in the accumulation of pollutants. Comparing with inversion at higher level, the inversion near the ground has significantly greater suppression effects on the diffusion. The pollution case from 17 December to 21 December lasts 5 days and PM_2.5 mass concentrations are higher than the case from 3 November to 5 November in 2016. It suggests that the vertical diffusion of pollutants is suppressed for longer time and contaminants accumulate on the ground with the temperature inversion. On the other hand, the horizontal wind speed is lower, and pollutants cannot spread horizontally which aggravate pollution. Concentrations of OC and EC in PM₁₀ at Gucheng in Hebei in two cases are also significantly different. Much higher OC, EC and OC/EC concentrations on 22 December are observed than on 3 November 2016, which may indicate more automobile exhaust and coal combustion in this heavy pollution event. The continuous appearance of the inversion layer, lower horizontal wind speed and more coal combustion and vehicle exhaust emissions are the main causes for this heavy pollution process.