Articles | Volume 11, issue 4
Research article
05 Apr 2018
Research article |  | 05 Apr 2018

Measurement of formic acid, acetic acid and hydroxyacetaldehyde, hydrogen peroxide, and methyl peroxide in air by chemical ionization mass spectrometry: airborne method development

Victoria Treadaway, Brian G. Heikes, Ashley S. McNeill, Indira K. C. Silwal, and Daniel W. O'Sullivan

Abstract. A chemical ionization mass spectrometry (CIMS) method utilizing a reagent gas mixture of O2, CO2, and CH3I in N2 is described and optimized for quantitative gas-phase measurements of hydrogen peroxide (H2O2), methyl peroxide (CH3OOH), formic acid (HCOOH), and the sum of acetic acid (CH3COOH) and hydroxyacetaldehyde (HOCH2CHO; also known as glycolaldehyde). The instrumentation and methodology were designed for airborne in situ field measurements. The CIMS quantification of formic acid, acetic acid, and hydroxyacetaldehyde used I cluster formation to produce and detect the ion clusters I(HCOOH), I(CH3COOH), and I(HOCH2CHO), respectively. The CIMS also produced and detected I clusters with hydrogen peroxide and methyl peroxide, I(H2O2) and I(CH3OOH), though the sensitivity was lower than with the O2 (CO2) and O2 ion clusters, respectively. For that reason, while the I peroxide clusters are presented, the focus is on the organic acids. Acetic acid and hydroxyacetaldehyde were found to yield equivalent CIMS responses. They are exact isobaric compounds and indistinguishable in the CIMS used. Consequently, their combined signal is referred to as the acetic acid equivalent sum. Within the resolution of the quadrupole used in the CIMS (1 mz), ethanol and 1- and 2-propanol were potential isobaric interferences to the measurement of formic acid and the acetic acid equivalent sum, respectively. The CIMS response to ethanol was 3.3 % that of formic acid and the response to either 1- or 2-propanol was 1 % of the acetic acid response; therefore, the alcohols were not considered to be significant interferences to formic acid or the acetic acid equivalent sum. The multi-reagent ion system was successfully deployed during the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) in 2014. The combination of FRAPPÉ and laboratory calibrations allowed for the post-mission quantification of formic acid and the acetic acid equivalent sum observed during the Deep Convective Clouds and Chemistry Experiment in 2012.

Short summary
A multi-reagent ion chemical ionization mass spectrometer was developed to quantify formic acid, acetic acid and hydroxyacetaldehyde (referred to as acetic acid equivalent sum, AAES), hydrogen peroxide and methyl peroxide. This set-up was successfully deployed in the field during the 2014 Front Range Air Pollution and Photochemistry Exp. Laboratory and field work allowed the post-mission quantification of both formic acid and AAES sum during the 2012 Deep Convective Clouds and Chem. Exp.