Markovic Milos Z, VandenBoer Trevor C, Murphy Jennifer G
Department of Chemistry, University of Toronto, Toronto, ON, Canada.
J Environ Monit. 2012 Jul;14(7):1872-84. doi: 10.1039/c2em00004k. Epub 2012 Apr 26.
In this work we present the results of extensive characterization and optimization of the Ambient Ion Monitor-Ion Chromatograph (AIM-IC) system, an instrument developed by URG Corp. and Dionex Inc. for simultaneous hourly measurements of the water-soluble chemical composition of atmospheric fine particulate matter (PM(2.5)) and associated precursor gases. The sampling assembly of the AIM-IC consists of an inertial particle size-selection assembly, a parallel-plate wet denuder (PPWD) for the collection of soluble gases, and a particle supersaturation chamber (PSSC) for collection of particles, in series. The analytical assembly of the AIM-IC consists of anion and cation IC units. The system detection limits were determined to be 41 ppt, 5 ppt, and 65 ppt for gas phase NH(3(g)), SO(2(g)), and HNO(3(g)) and 29 ng m(-3), 3 ng m(-3), and 45 ng m(-3) for particle phase NH(4)(+), SO(4)(2-), and NO(3)(-) respectively. From external trace gas calibrations with permeation sources, we determined that the AIM-IC is biased low for NH(3(g)) (11%), SO(2(g)) (19%), and HNO(3(g)) (12%). The collection efficiency of SO(2(g)) was found to strongly depend on the composition of the denuder solution and was found to be the most quantitative with 5 mM H(2)O(2) solution for mixing ratios as high as 107 ppb. Using a cellulose membrane in the PPWD, the system responded to changes in SO(2(g)) and HNO(3(g)) within an hour, however for NH(3(g)), the timescale can be closer to 20 h. With a nylon membrane, the instrument response time for NH(3(g)) was significantly improved, becoming comparable to the responses for SO(2(g)) and HNO(3(g)). Performance of the AIM-IC for collection and analysis of PM(2.5) was evaluated by generating known number concentrations of ammonium sulfate and ammonium nitrate particles (with an aerodynamic diameter of 300 nm) under laboratory conditions and by comparing AIM-IC measurements to measurements from a collocated Aerosol Mass Spectrometer (AMS) during a field-sampling campaign. On average, the AIM-IC and AMS measurements agreed well and captured rapid ambient concentration changes at the same time. In this work we also present a novel inlet configuration and plumbing for the AIM-IC which minimizes sampling inlet losses, reduces peak smearing due to sample carryover, and allows for tower-height sampling from the base of a research tower.
在本研究中，我们展示了对环境离子监测仪 - 离子色谱仪（AIM - IC）系统进行广泛表征和优化的结果。该仪器由URG公司和戴安公司联合开发，用于每小时同时测量大气细颗粒物（PM(2.5)）的水溶性化学成分及其相关前驱气体。AIM - IC的采样组件由一个惯性粒度选择组件、一个用于收集可溶性气体的平行板湿式洗涤器（PPWD）和一个用于收集颗粒的颗粒过饱和室（PSSC）串联组成。AIM - IC的分析组件由阴离子和阳离子离子色谱单元组成。该系统对气相NH(3(g))、SO(2(g))和HNO(3(g))的检测限分别确定为41 ppt、5 ppt和65 ppt，对颗粒相NH(4)(+)、SO(4)(2 -)和NO(3)( -)的检测限分别为29 ng m(-3)、3 ng m(-3)和45 ng m(-3)。通过使用渗透源进行外部痕量气体校准，我们确定AIM - IC对NH(3(g))（偏差11%）、SO(2(g))（偏差19%）和HNO(3(g))（偏差12%）存在偏低偏差。发现SO(2(g))的收集效率强烈依赖于洗涤器溶液的成分，并且发现对于高达107 ppb的混合比，使用5 mM H(2)O(2)溶液时收集效率最高。在PPWD中使用纤维素膜时，系统在一小时内对SO(2(g))和HNO(3(g))的变化做出响应，然而对于NH(3(g))，响应时间可能接近20小时。使用尼龙膜时，仪器对NH(3(g))的响应时间显著改善，变得与对SO(2(g))和HNO(3(g))的响应相当。通过在实验室条件下生成已知数量浓度的硫酸铵和硝酸铵颗粒（空气动力学直径为300 nm），以及在现场采样活动中将AIM - IC的测量结果与并置的气溶胶质谱仪（AMS）的测量结果进行比较，评估了AIM - IC对PM(2.5)的收集和分析性能。平均而言，AIM - IC和AMS的测量结果吻合良好，并且同时捕捉到了快速的环境浓度变化。在本研究中，我们还展示了一种用于AIM - IC的新型进样口配置和管道系统，该配置可将采样进样口损失降至最低，减少因样品残留导致的峰展宽，并允许从研究塔底部进行塔高采样。
