Airborne and ground-based observations of ammonium-nitrate-dominated aerosols in a shallow boundary layer during intense winter pollution episodes in northern Utah
Airborne and ground-based observations of ammonium-nitrate-dominated aerosols in a shallow boundary layer during intense winter pollution episodes in northern Utah
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DOI：
10.5194/acp-18-17259-2018
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发表时间：
2018-12
影响因子：
6.3
通讯作者：
A. Franchin;D. Fibiger;L. Goldberger;E. McDuffie;A. Moravek;C. Womack;E. Crosman;K. Docherty;W. Dubé;S. Hoch;B. H. Lee;R. Long;J. Murphy;J. Thornton;S. Brown;M. Baasandorj;A. Middlebrook
中科院分区：
文献类型：
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作者：
A. Franchin;D. Fibiger;L. Goldberger;E. McDuffie;A. Moravek;C. Womack;E. Crosman;K. Docherty;W. Dubé;S. Hoch;B. H. Lee;R. Long;J. Murphy;J. Thornton;S. Brown;M. Baasandorj;A. Middlebrook
抽象的。在美国犹他州北部的三个山谷中获得了气溶胶浓度、化学成分和气相前体的机载和地面测量结果。这些测量是 2017 年 1 月至 2 月进行的犹他州冬季细颗粒物研究 (UWFPS) 的一部分。PM1 气溶胶总质量浓度是通过双水獭飞机上的气溶胶质谱仪 (AMS) 测量的。 PM1 浓度范围从清洁时期的低于 2 µg m−3 到污染最严重时期的超过 100 µg m−3，与地面站点同时测量的 PM2.5 总质量浓度一致。在整个区域，总气溶胶质量增加到~2 µg m−3 以上与硝酸铵质量分数的增加相关，这清楚地表明该区域最高的气溶胶质量负荷主要归因于硝酸铵的增加。总气溶胶质量浓度高于 17.5 µg m−3 时，化学成分在区域上是均匀的，其中含有 74±5%（平均值±标准差）硝酸铵、18±3% 有机物质、6±3% 硫酸铵和 2±2% 氯化铵。该区域气溶胶质量和体积的垂直分布显示，污染边界层中浓度随高度变化。在污染事件期间，在所有三个山谷中，在离地面最初几百米内观察到较高的平均质量浓度。污染期间硝酸（HNO3）和氨（NH3）的气相测量表明，在卡什和犹他山谷，无机半挥发物向气溶胶相的分配通常受到气相硝酸量的限制，其中NH3过量。将无机物质与 ISORROPIA 热力学模型进行比较。计算总硝酸盐和总铵的各种减少量的总无机气溶胶质量浓度。对于污染事件，我们模拟总硝酸盐减少 50%，导致 PM1 总质量减少 46±3%。模拟总铵减少 50% 导致整个研究区域的总 PM1 质量减少 36±17% µg m−3。尽管各地之间存在一些差异，但我们的结果表明，在最低总硝酸盐条件下，对硝酸浓度降低的敏感性更高，以及氨的重要性。在盐湖谷，HNO3 和 NH3 浓度都控制着气溶胶的形成。
Abstract. Airborne and ground-based measurements of aerosol concentrations, chemical composition, and gas-phase precursors were obtained in three valleys in northern Utah (USA). The measurements were part of the Utah Winter Fine Particulate Study (UWFPS) that took place in January–February 2017. Total aerosol mass concentrations of PM1 were measured from a Twin Otter aircraft, with an aerosol mass spectrometer (AMS). PM1 concentrations ranged from less than 2 µg m−3 during clean periods to over 100 µg m−3 during the most polluted episodes, consistent with PM2.5 total mass concentrations measured concurrently at ground sites. Across the entire region, increases in total aerosol mass above ∼2 µg m−3 were associated with increases in the ammonium nitrate mass fraction, clearly indicating that the highest aerosol mass loadings in the region were predominantly attributable to an increase in ammonium nitrate. The chemical composition was regionally homogenous for total aerosol mass concentrations above 17.5 µg m−3, with 74±5 % (average ± standard deviation) ammonium nitrate, 18±3 % organic material, 6±3 % ammonium sulfate, and 2±2 % ammonium chloride. Vertical profiles of aerosol mass and volume in the region showed variable concentrations with height in the polluted boundary layer. Higher average mass concentrations were observed within the first few hundred meters above ground level in all three valleys during pollution episodes. Gas-phase measurements of nitric acid (HNO3) and ammonia (NH3) during the pollution episodes revealed that in the Cache and Utah valleys, partitioning of inorganic semi-volatiles to the aerosol phase was usually limited by the amount of gas-phase nitric acid, with NH3 being in excess. The inorganic species were compared with the ISORROPIA thermodynamic model. Total inorganic aerosol mass concentrations were calculated for various decreases in total nitrate and total ammonium. For pollution episodes, our simulations of a 50 % decrease in total nitrate lead to a 46±3 % decrease in total PM1 mass. A simulated 50 % decrease in total ammonium leads to a 36±17 % µg m−3 decrease in total PM1 mass, over the entire area of the study. Despite some differences among locations, our results showed a higher sensitivity to decreasing nitric acid concentrations and the importance of ammonia at the lowest total nitrate conditions. In the Salt Lake Valley, both HNO3 and NH3 concentrations controlled aerosol formation.