Abstract. A method is presented to quantify the low-molecular weight organic acids formic, acetic, propionic, butyric, pyruvic, glycolic, oxalic, malonic, succinic, malic, glutaric, and methanesulfonic acid in the atmospheric gas and particle phase in a two-hourly time resolution, based on a combination of the Monitor for AeRosols and Gases in ambient Air (MARGA) and an additional ion chromatography (IC) instrument. 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 both for isocratic and for 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 7.1 ng m−3 for methanesulfonate and 150.3 ng m−3 for pyruvate. 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 organic acid IC systems 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 553 ng m−3 for acetic acid, followed by formic (286 ng m−3), pyruvic acid (182 ng m−3), propionic (179 ng m−3), butyric (98 ng m−3) and glycolic (71 ng m−3). Particulate glycolate, oxalate and methanesulfonate were quantified with mean concentrations of 63 ng m−3, 74 ng m−3 and 35 ng m−3, respectively. Elevated concentrations in the late afternoon of gas phase formic acid and particulate oxalate indicate a photochemical formation.
Development of an online-coupled MARGA upgrade for the two-hourly quantification of low-molecular weight organic acids in the gas and particle-phase
