The second ACTRIS inter-comparison (2016) for Aerosol Chemical Speciation Monitors (ACSM): Calibration protocols and instrument performance evaluations

This work describes results obtained from the 2016 Aerosol Chemical Speciation Monitor (ACSM) intercomparison exercise performed at the Aerosol Chemical Monitor Calibration Center (ACMCC, France). Fifteen quadrupole ACSMs (Q_ACSM) from the European Research Infrastructure for the observation of Aerosols, Clouds and Trace gases (ACTRIS) network were calibrated using a new procedure that acquires calibration data under the same operating conditions as those used during sampling and hence gets information representative of instrument performance. The new calibration procedure notably resulted in a decrease in the spread of the measured sulfate mass concentrations, improving the reproducibility of inorganic species measurements between ACSMs as well as the consistency with co-located independent instruments. Tested calibration procedures also allowed for the investigation of artifacts in individual instruments, such as the overestimation of <i>m</i>/<i>z</i> 44 from organic aerosol. This effect was quantified by the <i>m</i>/<i>z</i> (mass-to-charge) 44 to nitrate ratio measured during ammonium nitrate calibrations, with values ranging from 0.03 to 0.26, showing that it can be significant for some instruments. The fragmentation table correction previously proposed to account for this artifact was applied to the measurements acquired during this study. For some instruments (those with high artifacts), this fragmentation table adjustment led to an “overcorrection” of the <i>f44</i> (<i>m</i>/<i>z</i> 44/Org) signal. This correction based on measurements made with pure NH₄NO₃, assumes that the magnitude of the artifact is independent of chemical composition. Using data acquired at different NH₄NO₃ mixing ratios (from solutions of NH₄NO₃ and (NH₄)₂SO₄) we observe that the magnitude of the artifact varies as a function of composition. Here we applied an updated correction, dependent on the ambient NO₃ mass fraction, which resulted in an improved agreement in organic signal among instruments. This work illustrates the benefits of integrating new calibration procedures and artifact corrections, but also highlights the benefits of these intercomparison exercises to continue to improve our knowledge of how these instruments operate, and assist us in interpreting atmospheric chemistry.

本研究阐述了2016年于法国气溶胶监测校准中心（Aerosol Chemical Monitor Calibration Center, ACMCC）开展的气溶胶化学组分监测仪（Aerosol Chemical Speciation Monitor, ACSM）比对实验所得结果。来自欧洲气溶胶、云与痕量气体观测研究基础设施（European Research Infrastructure for the observation of Aerosols, Clouds and Trace gases, ACTRIS）网络的15台四极杆型气溶胶化学组分监测仪（quadrupole ACSMs, Q_ACSM），采用全新校准流程完成校准：该流程在与采样工况完全一致的条件下采集校准数据，因此可获取能够表征仪器实际性能的有效信息。该新型校准流程显著缩小了硫酸盐质量浓度测量值的离散程度，既提升了不同ACSM之间无机组分测量的重现性，也增强了其与同期部署的独立观测仪器测量结果的一致性。本次测试的校准流程还可用于探究单台仪器存在的测量伪迹，例如有机气溶胶对质荷比（mass-to-charge ratio, m/z）44信号的高估现象。该效应可通过硝酸铵校准过程中测得的m/z44与硝酸盐的比值进行量化，其取值范围为0.03至0.26，表明该效应对部分仪器而言影响较为显著。此前为修正该测量伪迹提出的裂解表校正法，被应用于本研究的全部测量数据。对于部分存在较严重伪迹的仪器，该裂解表调整会对f44（即m/z44与有机组分的比值）信号产生“过度校正”。该基于纯硝酸铵测量所建立的校正方法，假设测量伪迹的幅值与化学组分无关。通过使用不同硝酸铵混合比（由硝酸铵与硫酸铵溶液配制）下获取的实验数据，我们发现该测量伪迹的幅值会随组分组成变化而改变。本次研究采用了一种更新后的校正方法，该方法依赖于环境大气中硝酸盐的质量分数，最终实现了不同仪器间有机组分信号一致性的显著提升。本研究既验证了整合新型校准流程与测量伪迹校正方法的应用价值，同时也凸显了此类仪器比对实验的重要意义：它们有助于持续深化我们对这类仪器运行机制的认知，并辅助我们更准确地解读大气化学相关观测数据。