High gas-phase mixing ratios of formic and acetic acid in the High Arctic

Abstract

Abstract. Formic and acetic acid are ubiquitous and abundant in the Earth's atmosphere and are important contributors to cloud water acidity, especially in remote regions. Their global sources are not well understood, as evidenced by the inability of models to reproduce the magnitude of measured mixing ratios, particularly at high northern latitudes. The scarcity of measurements at those latitudes is also a hindrance to understanding these acids and their sources. Here, we present ground-based gas-phase measurements of formic acid (FA) and acetic acid (AA) in the Canadian Arctic collected at 0.5 Hz with a high-resolution chemical ionization time-of-flight mass spectrometer using the iodide reagent ion (iodide HR-ToF-CIMS, Aerodyne). This study was conducted at Alert, Nunavut, in the early summer of 2016. FA and AA mixing ratios for this period show high temporal variability and occasional excursions to very high values (up to 11 and 40 ppbv respectively). High levels of FA and AA were observed under two very different conditions: under overcast, cold conditions during which physical equilibrium partitioning should not favor their emission, and during warm and sunny periods. During the latter, sunny periods, the FA and AA mixing ratios also displayed diurnal cycles in keeping with a photochemical source near the ground. These observations highlight the complexity of the sources of FA and AA, and suggest that current chemical transport model implementations of the sources of FA and AA in the Arctic may be incomplete.

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

“…amount of formic and acetic acid measured at the semiurban site Bondville, United States, is around 0.6 and 1 µg m −3 , respectively (Ullah et al, 2006). Nah et al (2018a) detected averaged concentrations of formic and acetic acid of 2.2 and 1.9 µg m −3 , respectively, at the rural Yorkville, Georgia, site.…”

“…For the three highest HONO concentrations during the measurement campaign (on average 5.1 µg m −3 ) only 66.2 ng m −3 of particle-phase NO − 2 was observed, resulting in a maximum HONO breakthrough of 1.3 %. The same calculation was performed for formic and acetic acid, which are most abundant in the gas phase (Nah et al, 2018a), resulting in a potential maximal breakthrough of 0.7 % and 0.1 %, respectively. Thus, the calculated denuder efficiencies are in same range with the experimental derived ones reported in the literature.…”

“…As a comparison, Parworth et al (2017) detected average glycolate concentrations of 26.7 ng m −3 with a nighttime maximum of around 60 ng m −3 in Fresno during winter. Mean concentrations of particulate oxalate, acetate and formate of 0.07, 0.06 and 0.05 µg m −3 , respectively, were measured by Nah et al (2018a). Van Pinxteren et al (2014) presented oxalate concentrations measured by impactors in Melpitz during autumn.…”

“…Gas-phase concentrations on the ground were monitored with a chemical ionization mass spectrometer (CIMS) (Veres et al, 2011;J. M. Liu et al, 2012;Crisp et al, 2014;Mungall et al, 2018). This instrument also enabled airborne measurements of formic acid (Jones et al, 2014).…”

“…Recently, Nah et al (2018a) presented measurements of low-molecular-weight organic acids within the gas and particle phases with the use of a CIMS and a particle-intoliquid sampler (PILS) coupled with capillary high-pressure ion chromatography (HPIC). They received hourly concentrations of these compounds at a rural southeastern United States site for 1 month and were able to investigate the gasparticle partitioning.…”