A Comparison Between a Semi-Continuous Analyzer and Filter-Based Method for Measuring Anion and Cation Concentrations in PM10 at an Urban Background Site in London

A comparison between the filter-based, laboratory ion chromatography technique and a semi-continuous analyzer (URG 9000B Ambient Ion Monitor [AIM]) was conducted to evaluate the performance of the AIM in measuring the concentrations of the main airborne ionic species in PM10. The study was carried out in an urban background area of London (UK) in 2013. The two methods showed an overall good correlation (R-2 > 0.83) for nitrate, sulfate, chloride, ammonium, and magnesium and poor correlation was found for sodium, potassium, and calcium (R-2 < 0.50). The AIM gave consistently higher concentrations for sodium and potassium, possibly due to a positive bias within the sampling unit. During high concentration episodes, both the efficiency of the particle extraction and removal of gases by the denuder may be reduced. A HEPA filter test demonstrated that the denuder was removing gaseous components effectively but that there was some potential for contamination. Overall, the AIM was found to be a good instrument for measuring hourly anion and cation concentrations in PM10 in urban sites.