Development of an online-coupled MARGA upgrade for the 2 h interval quantification of low-molecular-weight organic acids in the gas and particle phases

Abstract

Abstract. A method is presented to quantify the low-molecular-weight organic acids such as formic, acetic, propionic, butyric, pyruvic, glycolic, oxalic, malonic, succinic, malic, glutaric, and methanesulfonic acid in the atmospheric gas and particle phases, based on a combination of the Monitor for AeRosols and Gases in ambient Air (MARGA) and an additional ion chromatography (Compact IC) instrument. Therefore, every second hourly integrated MARGA gas and particle samples were collected and analyzed by the Compact IC, resulting in 12 values per day for each phase. A proper separation of the organic target acids was initially tackled by a laboratory IC optimization study, testing different separation columns, eluent compositions and eluent flow rates for both isocratic and gradient elution. Satisfactory resolution of all compounds was achieved using a gradient system with two coupled anion-exchange separation columns. Online pre-concentration with an enrichment factor of approximately 400 was achieved by solid-phase extraction consisting of a methacrylate-polymer-based sorbent with quaternary ammonium groups. The limits of detection of the method range between 0.5 ng m−3 for malonate and 17.4 ng m−3 for glutarate. Precisions are below 1.0 %, except for glycolate (2.9 %) and succinate (1.0 %). Comparisons of inorganic anions measured at the TROPOS research site in Melpitz, Germany, by the original MARGA and the additional Compact IC are in agreement with each other (R2 = 0.95–0.99). Organic acid concentrations from May 2017 as an example period are presented. Monocarboxylic acids were dominant in the gas phase with mean concentrations of 306 ng m−3 for acetic acid, followed by formic (199 ng m−3), propionic (83 ng m−3), pyruvic (76 ng m−3), butyric (34 ng m−3) and glycolic acid (32 ng m−3). Particulate glycolate, oxalate and methanesulfonate were quantified with mean concentrations of 26, 31 and 30 ng m−3, respectively. Elevated concentrations of gas-phase formic acid and particulate oxalate in the late afternoon indicate photochemical formation as a source.

Strong Deviations from Thermodynamically Expected Phase Partitioning of Low-Molecular-Weight Organic Acids during One Year of Rural Measurements

“…One-hour gas-and particle-phase samples were collected in parallel every second hour, pumped to an external autosampler, and successively transported to a specialized ion chromatography system (Compact IC, Metrohm, Switzerland) for the quantification of low-molecular-weight carboxylic acids (CA) and MSA with low risks of interferences, good repeatabilities below 3%, and detection limits in the range of 0.5 to 17.4 ng m −3 . 70 This setup allowed for determining hourly mean concentrations every other hour within a 2 h analysis run cycle. Compounds analyzed included formic, acetic, propionic, butyric, pyruvic, glycolic, oxalic, malonic, succinic, malic, glutaric, and methanesulfonic acid in addition to inorganic fluoride (F − ), chloride (Cl − ), nitrite (NO 2 − ), nitrate (NO 3 − ), and sulfate (SO 4 2− ).…”

“…The operating time of the system and the data availability of each compound during the campaign are presented in the Supporting Information (section S1 with Table S1 and Figure S1). Collection efficiencies and potential sampling artifacts of the WRD were discussed in detail by Stieger et al 70 Negligible interferences from a potential breakthrough of gases or a collection of particles within the WRD were reported.…”

“…The mean H emp value of MSA was approximately four orders of magnitude lower than H lit (Table 3) with all individual data points below the 1:1 line during the complete measurement campaign (Figure 2f). Instrumental losses by the MARGA system could be excluded in Stieger et al 70 A strong bias from the 0.5 × LOD approach for gas-phase concentrations below the LOD can also be excluded, as only 13.6% of gas-phase MSA data were below the LOD.…”

A Sampler for Collecting Fine Particles into Liquid Suspensions

“…In PILS, the grown droplets are collected by a single-nozzle impactor, and the liquid sample collected on the impactor surface is removed by a small, constant flow of purified water that also contains an internal standard. Both SJAC and PILS have been adopted for online measurements of ionic components of PM in combination of ion chromatograph (IC) (Perrino et al, 2015;Stieger et al, 2019). A similar aerosol sampler was introduced by Wubulihairen et al (2015a, b), in which a condensed water splitter is included to prevent sample dilution.…”

Development, characterization and application of an improved online reactive oxygen species analyzer based on MARGA

“…instrument. And it is not only used in many research institutes for long-term ion observation but also used to transform the observation of low-molecular-weight organic acids in the gas and particle phases (Stieger et al, 2019). MARGA is used to collect particulate matter and is connected to the optimized DTTV detection part to observe the oxidation potential hour by hour.…”