Gas-Phase Carboxylic Acids in a University Classroom: Abundance, Variability, and Sources

Abstract

Gas-phase carboxylic acids are ubiquitous in ambient air, yet their indoor occurrence and abundance are poorly characterized. To fill this gap, we measured gas-phase carboxylic acids in real-time inside and outside of a university classroom using a high-resolution time-of-flight chemical ionization mass spectrometer (HRToF-CIMS) equipped with an acetate ion source. A wide variety of carboxylic acids were identified indoors and outdoors, including monoacids, diacids, hydroxy acids, carbonyl acids, and aromatic acids. An empirical parametrization was derived to estimate the sensitivity (ion counts per ppt of the analytes) of the HRToF-CIMS to the acids. The campaign-average concentration of carboxylic acids measured outdoors was 1.0 ppb, with the peak concentration occurring in daytime. The average indoor concentration of carboxylic acids was 6.8 ppb, of which 87% was contributed by formic and lactic acid. While carboxylic acids measured outdoors displayed a single daytime peak, those measured indoors displayed a daytime and a nighttime peak. Besides indoor sources such as off-gassing of building materials, evidence for acid production from indoor chemical reactions with ozone was found. In addition, some carboxylic acids measured indoors correlated to CO in daytime, suggesting that human occupants may contribute to their abundance either through direct emissions or surface reactions.

Tropospheric sources and sinks of gas-phase acids in the Colorado Front Range

“…We hypothesize that reactions between O 3 and organic surfaces (i.e., soil, organic films) could be one non-photochemical surface-level source of alkanoic acids near the site, though unlikely to account for the entire source. Reactions of O 3 on organic surfaces such as organic films (Donaldson et al, 2005), plant surfaces (Cape et al, 2009;Jud et al, 2016), and human skin (Liu et al, 2016(Liu et al, , 2017 have been reported previously. Soil organic matter and organic films are often rich in alkenes (Vancampenhout et al, 2009;Donaldson et al, 2005;Simpson et al, 2006), which undergo ozonolysis reactions in the presence of O 3 (Criegee, 1975;Wolff et al, 1997).…”

Tropospheric sources and sinks of gas-phase acids in the Colorado Front Range

“…soil, organic films) could be one non-photochemical surface-level source of alkanoic acids near the site. Reactions of O3 on organic surfaces such as organic films (Donaldson et al, 2005), plant surfaces (Cape et al, 2009;Jud et al, 2016), and human skin (Liu et al, 2016;Liu et al, 2017) have been reported previously. Soil organic matter and organic films are often rich in alkenes (Vancampenhout et al, 2009;Donaldson et al, 2005;Simpson et al, 2006), 35 which undergo ozonolysis reactions in the presence of O3 (Criegee, 1975;Wolff et al, 1997).…”

Characterizing sources and emissions of volatile organic compounds in a northern California residence using space‐ and time‐resolved measurements

“…This analytical approach can measure speciated VOCs in real time, with second to minute resolution. Time‐resolved observations of speciated VOCs have been made in classrooms, cinemas, and football stadiums under normal occupancy, using proton transfer reaction time‐of‐flight mass spectrometry (PTR‐ToF‐MS), as well as other types of CIMS instruments . The high time resolution of this approach allows for exploring short–time‐scale processes, which are difficult to investigate using time‐integrated sampling.…”