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. A method is presented to quantify the low-molecular-weight organic acids suchasformic, acetic, propionic, butyric, pyruvic, glycolic, oxalic,malonic, succinic, malic, glutaric, and methanesulfonic acid in theatmospheric gas and particle phases, based on a combination of the Monitor forAeRosols and Gases in ambient Air (MARGA) and an additional ionchromatography (Compact IC) instrument. Therefore, every second hourlyintegrated MARGA gas and particle samples were collected and analyzed by theCompact IC, resulting in 12 values per day for each phase. A proper separationof the organic target acids was initially tackled by a laboratory ICoptimization study, testing different separation columns, eluent compositionsand eluent flow rates for both isocratic and gradient elution. Satisfactoryresolution of all compounds was achieved using a gradient system with twocoupled anion-exchange separation columns. Online pre-concentration with anenrichment factor of approximately 400 was achieved by solid-phase extractionconsisting of a methacrylate-polymer-based sorbent with quaternary ammoniumgroups. 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 below1.0 %, except for glycolate (2.9 %) and succinate (1.0 %).Comparisons of inorganic anions measured at the TROPOS research site inMelpitz, Germany, by the original MARGA and the additional Compact IC are inagreement with each other ( R2 =  0.95–0.99). Organic acid concentrationsfrom May 2017 as an example period are presented. Monocarboxylic acids weredominant in the gas phase with mean concentrations of 306 ng m −3 foracetic 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 andmethanesulfonate were quantified with mean concentrations of 26, 31 and30 ng m −3 , respectively. Elevated concentrationsof gas-phase formic acid and particulate oxalate in the late afternoon indicate photochemicalformation as a source.

atmospheric measurement techniques

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