稀释倍数对民用燃煤排放粒子老化及细粒子中多环芳烃的影响

With domestic coal combustion (DCC) as one of the most important sources,Polycyclic Aromatic Hydrocarbons (PAHs) in atmospheric fine particulate matter (PM2.5) exhibited negative impacts on human health. For studies on PM emitted from DCC, dilution sampling method is believed that it can simulate the real emission conditions of particles in smoke.Based on a self-designed dilution sampling system, the number concentrations and size distribution of particles, the growth rates of particles by nucleation under various dilution ratios (DR) and the influence of DR on the aging courses were analyzed by using a wide-range particle spectrometer (WPS). The best DR will be assured. The evolution trends of chemical species in different size of particles and the aging mechanism were studied by a Single Particle Aerosol Mass Spectrometer (SPAMS). Emission factors (EFs) for PAHs in five size-differentiated fine particles were established combined with the information of flow rates of smoke and coal consumption rates by adopting an individual five-size sampling inlets. The influence of DR on the EFs of PAHs was analyzed. This research will be useful to identify the aging mechanism of particles in smoke emitted from DCC and to establish the method for ascertaining the best DR of dilution sampling for combustion sources monitoring. Meanwhile, reliable EFs data will be obtained for establishing emission inventories of PAHs in atmospheric PM2.5.

大气细颗粒中PAHs严重危害人体健康，民用燃煤燃烧是其最重要的来源之一。稀释通道采样方法能更加真实地反应民用燃煤燃烧烟气中颗粒的排放状况，而稀释倍数是影响烟气中颗粒浓度和粒径分布的一个重要因素。本研究采用自主搭建的稀释通道采样系统，通过设置不同稀释倍数，采用宽范围颗粒粒径谱仪讨论烟气粒子粒数浓度和粒径分布特征及稀释倍数对烟气粒子老化过程的影响，获得相应的成核增长速率，确定最佳稀释倍数；采用单颗粒气溶胶质谱对民用燃煤燃烧排放不同粒径颗粒中化学组分的演化趋势进行监测分析，分析烟气粒子的老化机制；采用五级采样头并结合烟气流速、燃料消耗量等获得不同粒径细颗粒中PAHs排放因子，分析稀释倍数对细颗粒中PAHs组成的影响。本研究可为识别民用燃煤排放烟气中粒子的老化机制、建立稀释通道采样方法在燃烧源排放颗粒监测中最佳稀释倍数的确定方法及为大气细颗粒中PAHs排放清单的建立提供参考和借鉴。

我国中东部地区冬季持续重污染天气引起了广泛关注，尤其是冬季北方地区供暖耗煤排放污染物加重了污染过程。民用燃煤排放颗粒物及载带化学组分的粒径分布、气态前体物以及排放后的老化过程是当前研究的热点和难点。. 项目开展了民用燃煤室内模拟燃烧+稀释通道采样实验，选择3种蜂窝煤和4种块煤，设定闷烧和明烧两种燃烧状态，设定20、50、80、100和150倍5个稀释倍数。分析了稀释倍数对民用燃煤排放粒子老化过程的影响，分析了不同粒径颗粒中组分的演化，获得不同稀释倍数下民用燃煤排放分级气溶胶中组分排放因子。基于实测排放因子，初步构建了民用燃煤排放颗粒中关键化学组分清单。与国内外多家单位合作，对民用燃煤排放黑碳气溶胶、有机气溶胶、单颗粒气溶胶形态等开展了深入全面的研究，极大的拓展了本项目的影响力和成果产出数量和质量。. 结果表明，块煤燃烧排放重金属的排放因子各粒径段普遍大于蜂窝煤燃烧，排放因子是蜂窝煤明烧的2~7倍；蜂窝煤明烧重金属排放因子整体上大于闷烧，高2~6倍。民用煤燃烧排放水溶性离子排放因子峰值均出现在2.1 μm以下，尤其是0.43-0.65 μm。民用煤闷烧OC排放因子高于明烧；块煤EC排放因子高于蜂窝煤。闷烧PAHs排放因子高于明烧状态下PAHs排放因子；PAHs排放因子在0.43-0.65 μm出现峰值。不同产地块煤燃烧PAHs排放因子存在较大差异，内蒙古块煤PAHs排放因子比其它地区高约100倍。稀释倍数过小会低估OC和EC的排放因子；20-30倍的稀释倍数下，在峰值粒径段（94-150 nm）OC排放因子会被低估10倍；EC排放因子在该粒径段也会有近8倍的低估。气溶胶粒子数浓度大多在100 nm以下，闷烧时在大粒径段400-600 nm处多了一个峰值。碳组分、硫酸根、铵根、硝酸根、Cl-和重金属元素为主要组分，且在明烧时点火后1个小时左右出现峰值，并持续1个半小时。高分辨率空间分布显示民用燃煤排放组分分布表现为东部高于西部，平原和盆地多。. 本项目成果对于民用燃煤排放污染物的气候、环境和人体健康效应研究，具有重要意义。