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

Abstract

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. Although hydrogen peroxide and methyl peroxide also form cluster ions with I-, the focus here 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 m/z), 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 acetic 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.

Higher measured than modeled ozone production at increased NO<sub><i>x</i></sub> levels in the Colorado Front Range

“…PTR-ToF-MS (Müller et al, 2014) 10 U. Innsbruck methyl ethyl ketone, methanol, methyl vinyl ketone, methacrolein, acetic acid acetaldehyde, acetone formaldehyde DFGAS (Weibring et al, 2006(Weibring et al, , 2007 5 CU-INSTAAR peroxy acetyl nitrate, peroxy propyl nitrate PAN-CIMS (Zheng et al, 2011) 13 NCAR hydrogen peroxide, formic acid, acetic acid PCIMS (Treadaway, 2015) 30 URI ethanol, d-limonene/3-carene, TOGA 30 NCAR camphene a Denotes aircraft measurements. b CL, chemiluminescence; CES, cavity-enhanced spectroscopy; CAPS, cavity-attenuated phase shift spectrometer; WAC, whole-air canister; GC, gas chromatography; GC-MS, gas chromatography mass spectrometer; TD-LIF, thermal dissociation laser-induced fluorescence; PTR-ToF-MS, proton transfer reaction time-of-flight mass spectrometer; DFGAS, difference frequency generation absorption spectrometer; CIMS, chemical ionization mass spectrometer (PAN, peroxyacyl nitrate; P, peroxide); TOGA, trace organic gas analyzer.…”

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

“…In-flight calibrations were done as part of the FRAPPÉ program in the summer of 2014 with the second microfluidic setup. During FRAPPÉ the organic acid aqueous standards were verified by titration (Treadaway, 2015). The percent errors between the theoretical and titrated concentrations were 1.00 and 1.51 % for HFo and HAc, respectively.…”

“…Note that a variable critical orifice sample inlet was unavailable at the time of DC3 and, while available for FRAPPÉ, was not flown then to best evaluate the DC3 post-mission calibrations and their use in DC3 to recover HFo and HAc in that program. Consequently, instrument response in this work varied with sample inlet pressure or sample flow rate and was quantified in the laboratory and during FRAPPÉ (Treadaway, 2015;Heikes et al, 2017).…”

“…Liquid CH 3 I (SigmaAldrich, St. Louis, MO) was first evaporated into a gas cylinder and diluted with N 2 gas (Scott-Marrin). This CH 3 I mixture was further diluted with N 2 to a 5 ppm CH 3 I mixing ratio, which was found to reproduce the field sensitivities of HP, MHP, and H 18 2 O observed in DC3 (Treadaway, 2015 . Dilutions of both were standardized by titration and/or UV absorbance (M. .…”

“…The PCIMS system was originally developed for the DC3 experiment (O'Sullivan et al, 2018) and modified in post-mission calibration work. This modified system was then used in the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) (Treadaway, 2015) and modified again post-mission. The reason behind the post-mission DC3 development involves serendipity and foresight.…”