燃煤排放的碘对大气中亚微米颗粒物的贡献及其影响机制

Increasingly intense Urban haze is seriously affecting our nation image and damaging the public health. The key to brook no delay in treating haze is to control submicrometer particle(PM1). The main source of PM1 comes from the secondary production in atmosphere and emissions of combustion sources both of which mainly are produced by the secondary conversion of gas-particle. The key of the formation of PM1 by gas-particle conversion is the nucleation. Sulfate is the main species of the nucleation of the secondary particle. Iodine can enhance the retention rate of sulfate nucleation embryo more than one hundred times. Emissions by coal combustion is the main man-made source of iodine in atmosphere. The much higher content of iodine in inland cities' atmosphere than that in coastal atmosphere declares that iodine might greatly affect PM1. There is no research report about it up to present. Xinchang power plant and Huangjinpu power plant as well as their surroundings were selected as research areas with different environmental backgrounds and NOx emissions. Through monitoring the boiler flue gas and dust, the effect of iodine on PM1 and its particle distribution will be studied as well as the effect of boiler and pollution control equipment on the distribution of iodine in gas and particle. In different seasons and weather conditions, the effect of iodine on PM1 and its particle distribution will be investigated by monitoring atmosphere and PM1 around the power plants. The control mechanism of the effect of iodine on particle formation will be studied by smog chamber experiments. In this research, the contribution of iodine exhausted by coal burning to submicrometer particle in atmosphere and its influence mechanism will be made clear so as to find a new route to control the pollution of PM1 in urban areas.

愈演愈烈的城市灰霾严重影响我国形象、危害人群健康。治霾刻不容缓，其关键在控制亚微米颗粒物（PM1）。PM1主要来源为：空气中二次产生、燃烧源排放，两者都主要由气-粒转化二次生成。气-粒转化生成PM1的关键在成核。硫酸盐是二次颗粒物成核的主要物种。碘能使硫酸盐成核的存留率提高百倍。燃煤释放是大气碘的主要人为源，导致内陆城市大气碘含量犹高于沿海，昭示着其对PM1可能有较大影响，但迄今未见相关研究报道。选择环境背景和NOx排放差异明显的新昌电厂和黄金铺电厂及其周边为研究区。通过监测锅炉烟道沿途的烟气和粉尘，搞清碘对PM1及其粒度分布的影响，探求锅炉及污控设备对碘在气、粒分布的影响。在不同季节、天气，监测电厂周边空气和PM1，研究碘对PM1及其粒度分布的影响。进行烟雾箱实验，以揭示碘影响颗粒物形成的控制机制。本研究将搞清燃煤排放碘对大气PM1形成的贡献及其影响机制；为控制城市PM1污染探寻新的途径

大气气溶胶是环境的重要组成部分，其气候效应和环境意义越来越为人们所关注。大气中的碘元素的来源及所涉及的大气化学反应成为近年来大气化学和气溶胶生成研究的重点。内陆地区空气中的碘主要来源于燃煤，而随着燃煤电厂脱硫、脱硝以及颗粒物处理水平的提高，细颗粒物（PM2.5）成为燃煤排放的主要颗粒物。本课题对燃煤电厂下载灰进行粒径分级，并在实验室模拟采集亚微米颗粒物，测定不同粒径亚微米颗粒物的碘含量；对江西省南昌市新昌电厂和江西省余干县黄金埠电厂周边大气颗粒物进行采样分析，研究燃煤排放的碘对电厂烟气排放亚微米颗粒物的影响规律及其控制以及燃煤排放的碘对空气中亚微米颗粒物含量及粒度分布的影响；利用烟雾箱研究碘的形态与浓度，在各气象条件下对不同浓度的气体形成亚微米颗粒物的数量浓度和粒数分布的影响，探求各因子对颗粒物形成和增长的贡献。电厂周边大气亚微米颗粒物中以超细颗粒物为主，富含硅，呈规则的圆球状，其中核模态粒子数浓度占亚微米颗粒物的绝大多数。电厂周边环境中TSP和PM2.5呈现较高的日均质量浓度水平，对周边大气环境细颗粒物产生了一定的影响。离电厂不同距离处大气中亚微米颗粒物粒子数浓度呈现“单峰型”或者“双峰型”日变化规律，峰值出现的时间为9:00及傍晚17:00，一方面电厂燃烧排放的烟气会导致颗粒物数量的增加，另一方面，可能存在其他的人为源导致电厂周边大气亚微米颗粒物高于背景值。电厂周边气溶胶中碘含量水平5.2~19.2 ng·m-3之间，明显高于内陆上空含量水平0.7 ng·m-3。其中颗粒态碘是主要的存在形式，气溶胶中碘含量与大气中PM2.5质量浓度呈显著相关，与氨气浓度呈负相关。烟雾箱研究发现在干燥黑暗环境中，NO2、NO、NH3、SO2混合体系基加入碘后，粒子大量生成，且颗粒物数浓度和质量浓度均大于碘自身成核产生。本研究丰富、充实和发展碘的环境地球化学理论，证实了燃煤碘排放确实对城市大气亚微米颗粒物有重要贡献，将为政府采取有效措施控制烟霾开拓新的方法和途径。