Receptor model source attributions for Utah's Salt Lake City airshed and the impacts of wintertime secondary ammonium nitrate and ammonium chloride aerosol
Receptor model source attributions for Utah's Salt Lake City airshed and the impacts of wintertime secondary ammonium nitrate and ammonium chloride aerosol
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DOI：
10.1080/10962247.2013.774819
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发表时间：
2013-05-01
影响因子：
2.7
通讯作者：
Silcox, Geoffrey D.
中科院分区：
文献类型：
--
作者：
Kelly, Kerry E.;Kotchenruther, Robert;Silcox, Geoffrey D.
犹他州瓦萨奇前沿沿线的社区目前正在制定策略，以在冬季持续稳定的大气条件或冷空气池期间将每日平均 PM2.5 水平降低至国家环境空气质量标准以下。瓦萨奇锋线气域的 PM2.5 数据表明，冬季 PM2.5 超标主要是由高浓度的硝酸铵造成的。当存在足够的氮氧化物、氨和氧化能力时，稳定的冬季条件会促进硝酸铵气溶胶的形成。然而，这项工作表明，如果存在足够的大气氯源，二次氯化铵气溶胶也可能是冬季二次 PM2.5 的重要来源。使用正矩阵分解 (PMF) 和 Unmix 两种因子分析技术，确定了犹他州瓦萨奇前沿沿线三个监测站（Bountiful、Lindon 和盐湖城）PM2.5 的影响因素。监测数据包括 2007 年 5 月至 2011 年 5 月期间每个地点分别 227 天、227 天和 429 天的化学形态 PM2.5 数据。PMF 识别出每个地点的 1012 个因素，Unmix 识别出 45 个因素。冬季 PMF 和 Unmix 结果显示，当 PM2.5 浓度超过 20 g/m(3) 时，二次 PM2.5 的贡献很大。 PMF 确定硝酸铵和氯化铵气溶胶是冬季污染期间 PM2.5 的重要次要贡献者（氯化铵占总 PM2.5 的 1015%）。随后对监测数据的离子平衡分析证实，在这些高度污染的日子里，所有三个监测点均存在大量氯化铵气溶胶。源归因结果中直接排放的初级 PM2.5 部分与县级排放清单进行了进一步比较，结果显示，盐湖城和林顿在冬季除木烟和扬尘外总体上具有良好的一致性，除了木烟和扬尘，它们在受体建模结果中的贡献高于排放清单。启示：研究表明，在富含氨的环境中，二次氯化铵气溶胶可能是冬季 PM2.5 的重要来源， 如果存在足够的大气氯源，就像瓦萨奇锋线气域一样。冬季冷空气池事件期间，除木烟和炊事源外，源归因结果与县排放清单基本一致。在盐湖城监测站，木材烟雾和烹饪的估计贡献几乎是相应清单的两倍，这表明它们几乎与汽油排放一样重要。
Communities along Utah's Wasatch Front are currently developing strategies to reduce daily average PM2.5 levels to below National Ambient Air Quality Standards during wintertime persistent stable atmospheric conditions, or cold-air pools. Speciated PM2.5 data from the Wasatch Front airshed indicate that wintertime exceedances of the PM2.5 standard are mainly driven by high levels of ammonium nitrate. Stable wintertime conditions foster the formation of ammonium nitrate aerosol when sufficient sources of NOx, ammonia, and oxidative capacity exist. However, this work demonstrates that secondary ammonium chloride aerosol can also be a significant source of secondary wintertime PM2.5 if sufficient sources of atmospheric chlorine exist. Two factor analysis techniques, positive matrix factorization (PMF) and Unmix, were used to identify contributors to PM2.5 at three monitoring stations along Utah's Wasatch Front: Bountiful, Lindon, and Salt Lake City. The monitoring data included chemically speciated PM2.5 data for 227, 227, and 429 days at each location, respectively, during the period from May 2007 through May 2011. PMF identified 1012 factors and Unmix identified 45 factors for each of the locations. The wintertime PMF and Unmix results showed large contributions from secondary PM2.5 when PM2.5 concentrations exceeded 20 g/m(3). PMF identified both ammonium nitrate and ammonium chloride aerosol as significant secondary contributors to PM2.5 (1015% of total PM2.5 from ammonium chloride) during wintertime pollution episodes. Subsequent ion balance analysis of the monitoring data confirmed the presence of significant ammonium chloride aerosol on these highly polluted days at all three monitoring sites. The directly emitted primary PM2.5 portions of the source attribution results were further compared to county-level emissions inventories and showed generally good agreement for Salt Lake City and Lindon during wintertime except for wood smoke and fugitive dust, which have higher contributions in the receptor modeling results than in the emissions inventories.Implications: The study suggests that secondary ammonium chloride aerosol can be a significant source of wintertime PM2.5 in an ammonia-rich environment, like the Wasatch Front airshed, if sufficient sources of atmospheric chlorine exist. During wintertime, cold-air-pool events, the source attribution results generally agree with the county emission inventories with the exception of wood smoke and cooking sources. At the Salt Lake City monitoring station, the estimated contributions from wood smoke and cooking are nearly double those of the corresponding inventory, suggesting that they are nearly as important as gasoline emissions.