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.
A new and improved strategy combining a dispersive-solid phase extraction-based multiclass method with ultra high pressure liquid chromatography for analysis of low molecular weight polyphenols in vegetables
