An assessment of the performance of the Monitor for AeRosols and GAses in ambient air (MARGA): a semi-continuous method for soluble compounds

Abstract

Abstract. Ambient air monitoring as part of the US Environmental Protection Agency's (US EPA's) Clean Air Status and Trends Network (CASTNet) currently uses filter packs to measure weekly integrated concentrations. The US EPA is interested in supplementing CASTNet with semi-continuous monitoring systems at select sites to characterize atmospheric chemistry and deposition of nitrogen and sulfur compounds at higher time resolution than the filter pack. The Monitor for AeRosols and GAses in ambient air (MARGA) measures water-soluble gases and aerosols at an hourly temporal resolution. The performance of the MARGA was assessed under the US EPA Environmental Technology Verification (ETV) program. The assessment was conducted in Research Triangle Park, North Carolina, from 8 September to 8 October 2010 and focused on gaseous SO2, HNO3, and NH3 and aerosol SO42-, NO3-, and NH4+. Precision of the MARGA was evaluated by calculating the median absolute relative percent difference (MARPD) between paired hourly results from duplicate MARGA units (MUs), with a performance goal of ≤ 25%. The accuracy of the MARGA was evaluated by calculating the MARPD for each MU relative to the average of the duplicate denuder/filter pack concentrations, with a performance goal of ≤ 40%. Accuracy was also evaluated by using linear regression, where MU concentrations were plotted against the average of the duplicate denuder/filter pack concentrations. From this, a linear least squares line of best fit was applied. The goal was for the slope of the line of best fit to be between 0.8 and 1.2. The MARGA performed well in comparison to the denuder/filter pack for SO2, SO42−, and NH4+, with all three compounds passing the accuracy and precision goals by a significant margin. The performance of the MARGA in measuring NO3- could not be evaluated due to the different sampling efficiency of coarse NO3- by the MUs and the filter pack. Estimates of "fine" NO3- were calculated for the MUs and the filter pack. Using this and results from a previous study, it is concluded that if the MUs and the filter pack were sampling the same particle size, the MUs would have good agreement in terms of precision and accuracy. The MARGA performed moderately well in measuring HNO3 and NH3, though neither met the linear regression slope goals. However, recommendations for improving the measurement of HNO3 and NH3 are discussed. It is concluded that SO42-, SO2, NO3-, HNO3, NH4+, and NH3 concentrations can be measured with acceptable accuracy and precision when the MARGA is operated in conjunction with the recommendations outlined in the manuscript.

Persistent sulfate formation from London Fog to Chinese haze

“…The sampling site in Beijing (from 21 January to 4 February 2015) was located on the campus of Peking University in northwestern Beijing (21). Gaseous species and PM properties were monitored by a suite of instrumentations and methods (54)(55)(56)(57)(58)(59)(60)(61)(62)(63)(64). Laboratory experiments were performed to evaluate SO 2 oxidation by NO 2 on bulk solutions and aerosols under dark conditions (see also SI Appendix).…”

Water soluble aerosols and gases at a UK background site – Part 1: Controls of PM<sub>2.5</sub> and PM<sub>10</sub> aerosol composition

“…The performance of the MARGA has been further discussed by Rumsey et al (2014), Makkonen et al (2012), and Cowen et al (2011. The deployment of pre-concentration columns sets our MARGA instrument aside from the others, with the exception of Makkonen et al (2014), allowing quantitative detection of the low concentrations encountered at this clean Scottish site.…”

“…In particular, the wet chemistry MARGA instrument (Measurement of Aerosols and Reactive Gases Analyser, Metrohm Applikon B.V., NL) provides hourly measurements of water-soluble nitrate, chloride, sulfate, sodium, ammonium, potassium, magnesium and calcium (hereafter NO and Ca 2+ , respectively) in addition to the gas-phase basic and acid gases: ammonia, nitric acid, nitrous acid, hydrochloric acid and sulfur dioxide (hereafter NH 3 , HNO 3 , HONO, HCl, SO 2 , respectively) Rumsey et al, 2014;, based on aerosol collection via a steam-jet aerosol collector (SJAC; Khlystov et al, 1995). Other similar IC (ion chromatography) based systems are available, including the Ambient Ion Monitor-Ion Chromatograph system (AIM-IC, URG Corp. and Dionex Inc.) (Markovic et al, 2012) as well as the Particle into Liquid Sampler with Ion Chromatography (PILS-IC, Metrohm AG, Herisau, Switzerland), and a range of custom-built wetchemistry instruments based on the Particle Into Liquid Sampler (Weber et al, 2001).…”

Metrology for ammonia in ambient air – concept and first results of the EMRP project MetNH3

“…For applications requiring higher time resolution and on-line measurement, a series of wet chemical analyzers have been developed led by the Netherlands since the 1990s [17,18,19]. The most important advantages of these instruments are practically artefact-free gas handling, and the possibility of reliable and accurate calibration using liquid ammonium-solutions.…”