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Aerosol pH Indicator and Organosulfate Detectability from Aerosol Mass Spectrometry Measurements
Atmospheric Measurement Techniques ( IF 3.8 ) Pub Date : 2020-08-31 , DOI: 10.5194/amt-2020-339
Melinda K. Schueneman , Benjamin A. Nault , Pedro Campuzano-Jost , Duseong S. Jo , Douglas A. Day , Jason C. Schroder , Brett B. Palm , Alma Hodzic , Jack E. Dibb , Jose L. Jimenez

Abstract. Aerosol sulfate is a major component of submicron particulate matter (PM1). Sulfate can be present as inorganic (mainly ammonium sulfate, AS) or organic sulfate (OS). Although OS are thought to be a smaller fraction of total sulfate in most cases, recent literature argues that this may not be the case in more polluted environments. Aerodyne Aerosol Mass Spectrometers (AMS) measure total submicron sulfate, but it has been difficult to apportion AS vs. OS as the detected ion fragments are similar. Recently, two new methods have been proposed to quantify OS separately from AS with AMS data. We use observations collected during several airborne field campaigns covering a wide range of sources and airmass ages (spanning the continental US, marine remote troposphere, and Korea) and targeted laboratory experiments to investigate the performance and validity of the proposed OS methods. Four chemical regimes are defined to categorize the factors impacting sulfate fragmentation (Fig. shown in abstract). In polluted areas with high ammonium nitrate concentrations and in remote areas with high aerosol acidity, the decomposition and fragmentation of sulfate in the AMS is influenced by multiple complex effects, and estimation of OS does not seem possible with current methods. In regions with lower acidity (pH>0) and ammonium nitrate (fraction<0.3), the proposed OS methods might be more reliable, although application of these methods often produced nonsensical results. However, the fragmentation of ambient neutralized sulfate varies somewhat within studies, adding uncertainty, possibly due to variations in the effect of organics. Under highly acidic conditions, sulfate fragment ratios show a clear relationship with acidity (pH and ammonium balance). The measured ammonium balance (and to a lesser extent, the HySOx+/SOx+ AMS ratio) is a promising indicator for rapid estimation of aerosol pH < 0, including when gas-phase NH3 and HNO3 are not available. These results allow an improved understanding of important intensive properties of ambient aerosols.

中文翻译:

气溶胶质谱仪测量的气溶胶pH指示剂和有机硫酸盐可检测性

摘要。硫酸盐气雾剂是亚微米颗粒物(PM1)的主要成分。硫酸盐可以无机盐(主要是硫酸铵,AS)或有机硫酸盐(OS)的形式存在。尽管大多数情况下OS被认为是总硫酸盐的一小部分,但最近的文献认为,在污染更严重的环境中情况并非如此。Aerodyne气溶胶质谱仪(AMS)可测量总的亚微米硫酸盐,但由于检测到的离子碎片相似,因此很难区分AS与OS。近来,已经提出了两种新方法来与具有AMS数据的AS分开量化OS。我们使用在几次机载野战中收集到的观测资料,这些观测资料涵盖了广泛的来源和气团年龄(横跨美国大陆,海洋对流层,和韩国)和有针对性的实验室实验,以研究所建议的OS方法的性能和有效性。定义了四种化学方案以对影响硫酸盐裂解的因素进行分类(摘要显示图)。在硝酸铵浓度高的污染地区和气溶胶酸度高的偏远地区,AMS中硫酸盐的分解和破碎受到多种复杂效应的影响,用当前的方法估计OS似乎是不可能的。在酸度较低(pH> 0)和硝酸铵(馏分<0.3)的地区,尽管使用这些方法通常会产生无意义的结果,但所提出的OS方法可能更可靠。但是,环境中和的硫酸盐的碎片化在研究中有所不同,增加了不确定性,可能是由于有机物效果的差异。在高酸性条件下,硫酸盐碎片比率与酸度(pH和铵平衡)之间有着明显的关系。测得的铵平衡(在较小程度上,HySOx + / SOx + AMS比率)是快速估算气溶胶pH <0的有希望的指标,包括无法使用气相NH3和HNO3时。这些结果使人们可以更好地理解周围气溶胶的重要强度特性。
更新日期:2020-08-31
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