近3年西双版纳州勐腊县大气污染基本特征及污染原因分析

对西双版纳州生态环境局勐腊分局2017年8月-2020年8月逐日空气质量数据的分析表明，2-4月是勐腊县空气质量指数（Air Quality Index，AQI）频繁达到二级及以上的时段，空气质量分指数（Individual Air Quality Index，IAQI）能够达到二级及以上标准的污染物为PM_2.5、PM₁₀、O₃、SO₂中的一种或几种，PM_2.5、PM₁₀污染较为严重，PM_2.5对空气质量的影响最大，可使空气质量达到重度污染，混合污染出现比例远大于单一污染.2019、2020年3-4月勐腊县轻度及以上连续污染日数超过5 d的5次过程中，4次污染过程的主要潜在源区在勐腊上风方向老挝西北部及泰国与其相邻的区域，权重潜在源贡献因子（Weight Potential Source Contribution Function，WPSCF）大于0.6的区域与同年3、4月泰国西北部、老挝西北部的火点密集区有较好的对应关系，4次污染过程与老挝西北部及泰国与其相邻区域的生物质燃烧关系密切；1次污染过程的主要潜在源区主要在当地，当地建筑施工、交通运输、生物质燃烧和餐饮行业细颗粒物的排放会导致勐腊县空气质量出现明显下降.为验证勐腊县连续污染过程受到了周边国家烧荒的影响，利用逐日气溶胶光学厚度（Aerosol Optical Thickness，AOT）对2020年3月23-4月9日的污染过程进行了个例分析，发现AOT大值区位于勐腊上风方向，高浓度污染物持续稳定地向勐腊传输导致勐腊出现持续重污染.

Characteristics and causes of air pollution in Mengla County of Xishuangbanna prefecture in recent 3 years

Using the daily air quality data from August 2017 to August 2020 observed by Mengla branch of Xishuangbanna ecological environment bureau, the basic characteristics of air quality in Mengla County are analyzed. The AQI in Mengla County can reach and exceed grade II frequently from February to April, and the IAQI of PM_2.5, PM₁₀, O₃ or SO₂ can reach grade II or above. PM_2.5 and PM₁₀ can induce serious pollution, in which PM_2.5 has the greatest impacts on air quality and induces the air quality to reach the heavy pollution level. In all pollution events, the proportion of mixed pollution is much larger than that of single pollution. Five pollution events above mild level and lasting for more than 5 days in March and April in 2019 and 2020 were investigated by the WPSCF (Weight Potential Source Contribution Function) analysis, and results indicate that the potential sources of four pollution events located in northwest Laos and Thailand in the upwind direction of Mengla County and the areas with WPSCF greater than 0.6 corresponded to intensive fire areas in Northwest Thailand and northwest Laos in March and April. In addition, the potential source of the other pollution event included fine particulate emissions from local construction, transportation, biomass-burning and catering industry. The daily AOT (Aerosol Optical Thickness) was used to analyze the pollution event from March 23 to April 9, 2020, and high value of AOT located in the windward side of Mengla, which showed that the high concentration pollutants were continuously and stably transported to Mengla County, causing the heavy pollution event.