Abstract

The Aerodyne aerosol mass spectrometer (AMS) is used extensively to study the composition of non-refractory submicron aerosol composition during atmospheric field studies. During two recent studies of indoor environments, HOMEChem and ATHLETIC, the default ambient organic aerosol AMS quantification parameters resulted in a large discrepancy with co-located instruments while sampling cooking organic aerosol (COA). Instruments agreed within uncertainty estimates during all other sampling periods. Assuming a collection efficiency (CE) of unity, adjustments to the AMS relative ionization efficiency (RIE) were required to reach agreement with co-located instruments. The range of RIE_COA observed (ATHLETIC: RIE_COA = 4.26–4.96, HOMEChem: RIE_COA = 4.70–6.50) was consistent with RIE measured in the laboratory for cooking-specific molecules. These results agree with prior AMS studies which have indicated that more oxidized outdoor ambient organic aerosol has a relatively constant RIE of 1.4 ± 0.3 while more reduced organics have higher RIE. The applicability of a higher RIE was considered for two ambient datasets, and agreement between the AMS and co-located instruments improved when an increased response factor (RIE $\times$ CE) was applied to positive matrix factorization-derived primary organic aerosol (POA). Based on the observations presented here and the literature, we recommend AMS users consider applying RIE_COA=4.2 to source and indoor studies of COA and evaluate a higher POA response factor of the order of ∼1.5 in outdoor studies at urban background sites, and ∼2 at sites impacted by fresh sources. This study aims to improve AMS quantification methodology for reduced POA and highlights the importance of careful intercomparisons in field studies.

摘要

Aerodyne 气溶胶质谱仪 (AMS) 广泛用于在大气场研究期间研究非耐火亚微米气溶胶成分的成分。在最近对室内环境 HOMEChem 和 ATHLETIC 的两项研究中，默认的环境有机气溶胶 AMS 量化参数导致在采样烹饪有机气溶胶 (COA) 时与位于同一地点的仪器存在很大差异。在所有其他采样期间，仪器在不确定性估计内达成一致。假设收集效率 ( CE ) 为 1，则需要调整 AMS 相对电离效率 ( RIE ) 才能与共置仪器达成一致。观察到的RIE _COA范围（ATHLETIC：RIE _COA = 4.26–4.96，HOMEChem：RIE _COA  = 4.70–6.50）与实验室中针对烹饪特定分子测量的RIE一致。这些结果与先前的 AMS 研究一致，这些研究表明，更多氧化的室外环境有机气溶胶具有相对恒定的RIE，为 1.4 ± 0.3，而更多还原的有机物具有更高的RIE。考虑了两个环境数据集的更高RIE的适用性，当响应因子 ( RIE)增加时，AMS 和协同定位仪器之间的一致性得到改善 $\times$ CE ) 应用于正矩阵分解衍生的初级有机气溶胶 (POA)。根据此处提供的观察结果和文献，我们建议 AMS 用户考虑将RIE _COA = 4.2应用于_{COA 的}源和室内研究，并在城市背景站点的室外研究中评估更高的 POA 响应因子约为 1.5，并且 ∼ 2 在受新鲜来源影响的地点。本研究旨在改进 AMS 量化方法以减少 POA，并强调了实地研究中仔细比对的重要性。