A Comparison Between a Semi-Continuous Analyzer and Filter-Based Method for Measuring Anion and Cation Concentrations in PM₁₀at an Urban Background Site in London

Abstract

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 PM 10 . 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 PM 10 in urban sites.

Field and laboratory evaluation of a high time resolution x-ray fluorescence instrument for determining the elemental composition of ambient aerosols

“…The slopes were similar for the SO 4 (1.65) and Cl (1.68) and slightly higher for Ca (1.89). Deming regression for K resulted in a very high slope (4.55) but this 15 was likely the result of concentrations being close to the LOD for the URG, result was consistent with the findings presented by Beccaceci et al (2015). The R 2 for Ca, Cl, K and SO 4 was 0.86, 0.93, 0.36 and 0.95, respectively.…”

“…The higher concentrations measured by the XACT relative to the URG was likely caused by the low watersolubility of Cl, K, Ca and S containing minerals as well as the penetration efficiency of larger aerosols through 20 the URG annular denuder (Beccaceci et al 2015). The range of sources of these ions/elements resulted in variations in particle size and solubility and hence the relative response of the two instruments.…”

“…The URG-900B Ambient Ion Monitor continuously measured water-soluble anion and cation concentrations ) in PM 10 and is described in (Beccaceci et al, 2015). Briefly, the sample was drawn at a flow rate of 1 m 3 h -1 through a size selective inlet (PM10); the sample was then split isokinetically through a flow splitter to allow a 0.18 m 3 h -1 flow into a liquid diffusion denuder containing H 2 O 2 10 to remove interfering acidic and basic gases.…”

“…These include aerosol mass spectrometers such as the ACSM (Aerodyne Research Inc.) (Ng et al, 2011); ion chromatography approaches such as the MARGA (Metrohm) (Rumsey et al, 2014), PILS (Brechtel) (Weber et al, 2001) and URG's 9000 ambient ion monitor (Beccaceci et al, 2015); and x-ray fluorescence (XRF) such as the XACT instrument (Cooper Environmental Services) (Park et al, 2014). However, these high time resolution 20 instruments only measure a subset of chemical components each, depending on their collection, extraction and analysis methodology.…”

“…For the ACSM, the sulphate measurement uncertainty was estimated as 14% (k=2) for sulphate at a 30 min resolution by Crenn et al. (2015) and the LOD was determined using HEPA field blank measurements as 34.9 ng m -3.For the URG, the chloride and sulphate LODs were reported by the manufacturer as 100 ng m -3 and verified by Beccaceci et al (2015). The uncertainty of the species measured by ion chromatography was estimated at 4.5% (k=2) by 15 Yardley et al (2007) and combined with the additional 97% extraction efficiency of a particle-to-liquid sampler system estimated by Orsini et al (2003).…”