Elemental composition of ambient aerosols measured with high temporal resolution using an online XRF spectrometer

Abstract

Abstract. An Xact 625 ambient metals monitor was tested during a three-week field campaign at the rural, traffic-influenced site Härkingen in Switzerland during summer of 2015. The objective was to characterize the handling and operation of the instrument, evaluate the data quality by intercomparison with other independent measurements, and test its applicability for aerosol source quantification. The Xact was configured to measure 24 elements in PM10 with 1-h time resolution. Hourly element concentrations ranged from a few ng m−3 for trace elements in background conditions to tens of µg m−3 for major elements during a high-emission event (fireworks). The total Xact element mass comprised approximately 20 % of the total PM10 mass. The six major elements Si, S, Cl, K, Ca, and Fe contributed 95 % to the Xact PM10 mass, the remaining 5 % were attributed to the trace elements. Data quality was evaluated by intercomparison with 24-h PM10 filter data analysed with ICP-OES for major elements, ICP-MS for trace elements, and gold amalgamation atomic absorption spectrometry for Hg. 10 elements (S, K, Ca, Ti, Mn, Fe, Cu, Zn, Ba, Pb) showed an excellent correlation between the compared methods, with r2 values ≥ 0.95, even though the Xact 625 yielded approximately 28 % higher elemental concentrations than ICP for these elements. These elements demonstrate the high precision of the Xact instrument. An average 28 percent difference to ICP analyses might in part be attributed to the differences in the sampling systems (inlets), the geographic distance between the inlets and between the inlets and the freeway, and to uncertainties in the different analysis methods. 10 additional elements (Cr, V, Co, Ni, As, Se, Cd, Sn, Hg, Bi) could not be compared to a reference, because their concentrations were close to or below the minimum detection limits of at least one of the analysis methods. Sb revealed a calibration issue with the Xact, which requires correction. Si, Cl and Pt were not analysed with ICP, and thus could not be evaluated. The well-quantified elements were further used for a simple investigation of sources. The field campaign encompassed the Swiss National Day fireworks event, providing increased concentrations and unique chemical signatures compared to non-fireworks (or background) periods. Fireworks and traffic or rural background emissions could clearly be identified with their element mixture. The results demonstrate that multi-metal characterization at high-time resolution capability of Xact is a valuable and practical tool for ambient monitoring, exhibiting significant advantages compared to traditional elemental analysis methods.

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

“…For the XACT, the standards used in calibrations were much higher than ambient concentrations and the calibration matrix differed 35 from sample matrix (Indresand et al, 2013). Nevertheless, the results of the XACT comparison with ICP-MS in this study are comparable to those reported in other studies (Furger et al, 2017 …”

“…Nevertheless the analysis is still performed in the laboratory and thus does not improve the time delay of the analysis. Despite these limitations, the XACT is unique in measuring elements automatically using energy dispersive 30 XRF (ED-XRF) and has been successfully evaluated in a number of field studies (Furger et al, 2017;Park et al, 2014). Park et al (2014) found a good agreement between the XACT and 24 hour filter based measurement collected in South Korea (filters analysed using ED-XRF).…”

“…Furthermore, the high time resolution instruments tend to sample a narrower range of components with a higher Limit of Detection (LOD) than equivalent laboratory based methods, generally because less material is collected on each sample. For example, the synchrotron radiation-induced XRF (SR-XRF) used by 25 Visser et al (2015b) measured elements with atomic numbers greater than 11 while the XACT measures elements with atomic numbers greater than 14 thereby missing important contributors to PM mass such as Na, Mg and Al; the LODs reported for the SR-XRF analysis (Visser et al, 2015b) are generally lower than those for the XACT (Furger et al, 2017;Park et al, 2014).…”

“…Park et al (2014) found a good agreement between the XACT and 24 hour filter based measurement collected in South Korea (filters analysed using ED-XRF). Furger et al (2017) tested the XACT during a summer campaign in Switzerland in 2015 and compared the XACT data with measurements made using ICP-MS on filters sampled for 24 hours (both PM 10 ) as well as ACSM measurements (PM 1 ). They found an excellent 35 correlation, with R 2 values ≥ 0.95, between the XACT and ICP-MS data for ten elements (S, K, Ca, Ti, Mn, Fe, Cu, Zn, Ba, Pb).…”

First long-term and near real-time measurement of trace elements in China's urban atmosphere: temporal variability, source apportionment and precipitation effect

“…More recently, Aerosol Time-Of-Flight Mass Spectrometry (ATOFMS) (Murphy et al, 1998;Gross et al, 2000;DeCarlo et al, 2006), the National Institute for Standards and Technology (NIST)-traceable reference aerosol generating method (QAG) (Yanca et al, 2006), distance-based detection in a multi-layered device (Cate et al, 2015), environmental magnetic properties coupled with support vector machine , and the Xact 625 automated multi-metals analyzer (Fang et al, 2015;Jeong et al, 2016;Phillips-Smith et al, 2017;Cooper et al, 2010) have been developed for more precise, accurate and frequent measurement of ambient elemental species. The Xact method is based on nondestructive XRF analysis of aerosol deposits on a moving filter tape, which has been validated by the US Environmental Technology Verification testing and several other field campaigns (Fang et al, 2015;Phillips-Smith et al, 2017;Jeong et al, 2016;Yanca et al, 2006;Cooper et al, 2010;Park et al, 2014;Furger et al, 2017).…”