Tennessee Valley Authority, Muscle Shoals, Alabama 35662-1010, USA.
J Air Waste Manag Assoc. 2013 Jul;63(7):806-18. doi: 10.1080/10962247.2013.795201.
Dry fly ash disposal involves dropping ash from a truck and the movement of a heavy grader or similar vehicle across the ash surface. These operations are known to produce fugitive particulate emissions that are not readily quantifiable using standard emission measurement techniques. However there are numerous situations--such as applying for a source air permit--that require these emissions be quantified. Engineers traditionally use emission factors (EFs) derived from measurements of related processes to estimate fly ash disposal emissions. This study near a dry fly ash disposal site using state-of-the-art particulate monitoring equipment examines for the first time fugitive emissions specific to fly ash handling at an active disposal site. The study measured hourly airborne mass concentrations for particles smaller than 2.5 microm (PM2.5) and 10 microm (PM10) along with meteorological conditions and atmospheric turbidity at high temporal resolution to characterize and quantify fugitive fly ash emissions. Fugitive fly ash transport and dispersion were computed using the on-site meteorological data and a regulatory air pollutant dispersion model (AERMOD). Model outputs coupled with ambient measurements yielded fugitive fly ash EFs that averaged 96 g Mg(-1) (of ash processed) for the PM(c) fraction (= PM10 - PM2.5) and 18 g Mg(-1) for PM2.5. Median EFs were much lower due to the strongly skewed shape of the derived EF distributions. Fugitive EFs from nearby unpaved roads were also characterized. Our primary finding is that EFs for dry fly ash disposal are considerably less than EFs derived using US Environmental Protection Agency AP-42 Emissions Handbook formulations for generic aggregate materials. This appears to be due to a large difference (a factor of 10+) between fugitive vehicular EFs estimated using the AP-42 formulation for vehicles driving on industrial roads (in this case, heavy slow-moving grading equipment) and EFs derived by the current study.
Fugitive fly ash emission factors (EFs) derived by this study contribute to the small existing knowledge base for a type of pollutant that will become increasingly important as ambient particulate standards become tighter. In areas that are not in attainment with standards, realistic EFs can be used for compliance modeling and can help identify which classes of sources are best targeted to achieve desired air quality levels. In addition, understanding the natural variability in fugitive fly ash emissions can suggest methods that are most likely to be successful in controlling fugitive emissions related to dry fly ash storage.
干飞灰处置涉及从卡车上倾倒灰烬，以及重型平地机或类似车辆在灰面移动。这些操作会产生易挥发的颗粒物排放，使用标准排放测量技术不易量化。然而，有许多情况，例如申请源空气许可证，需要量化这些排放。工程师传统上使用从相关过程测量中得出的排放因子（EF）来估计飞灰处置排放。本研究在一个干飞灰处置场附近使用最先进的颗粒监测设备，首次检查了在一个活跃的处置场中专门处理飞灰的易挥发排放物。该研究以高时间分辨率测量了每小时小于 2.5 微米（PM2.5）和 10 微米（PM10）的空气中的质量浓度，以及气象条件和大气浊度，以表征和量化易挥发的飞灰排放物。使用现场气象数据和法规空气污染物扩散模型（AERMOD）计算了易挥发的飞灰运输和扩散。模型输出与环境测量结果相结合，得出了飞灰的易挥发排放因子，PM(c) 分数（= PM10-PM2.5）的平均值为 96 g Mg(-1)（处理的灰烬），PM2.5 为 18 g Mg(-1)。由于衍生的 EF 分布形状强烈偏斜，中位数 EF 要低得多。附近未铺砌道路的易挥发 EF 也得到了描述。我们的主要发现是，干飞灰处置的 EF 明显低于美国环境保护署 AP-42 排放手册中针对通用骨料材料的公式得出的 EF。这似乎是由于使用 AP-42 公式估计在工业道路上行驶的车辆（在这种情况下，是重型缓慢移动的平地机）的车辆易挥发 EF 与当前研究得出的 EF 之间存在很大差异（相差 10 倍以上）。
本研究得出的易挥发飞灰排放因子（EF）有助于填补一种污染物的现有知识库，随着环境颗粒物标准变得更加严格，这种污染物将变得越来越重要。在未达到标准的地区，可以使用现实的 EF 进行合规建模，并有助于确定哪些污染源类别最适合实现所需的空气质量水平。此外，了解易挥发飞灰排放的自然变化可以提出最有可能成功控制与干飞灰储存相关的易挥发排放的方法。
