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

• Published in: Atmospheric chemistry and physics Vol. 18; no. 14; pp. 10237 - 10254
• Main Authors: Mungall, Emma L, Abbatt, Jonathan P. D, Wentzell, Jeremy J. B, Wentworth, Gregory R, Murphy, Jennifer G, Kunkel, Daniel, Gute, Ellen, Tarasick, David W, Sharma, Sangeeta, Cox, Christopher J, Uttal, Taneil, Liggio, John
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 18-07-2018; Copernicus Publications
• Subjects: Acetic acid; Acidity; Acids; Analysis; Atmospheric models; Chemical properties; Chemical transport; Cloud water; Clouds; Earth; Earth atmosphere; Environmental aspects; Formic acid; Geochemical cycles; Ground-based observation; Iodides; Ionization; Latitude; Mass spectrometry; Mixing ratio; Organic chemistry; Photochemicals; Photochemistry; Reagents; Remote regions; Temporal variability; Temporal variations; Arctic; Arctic region
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-18-10237-2018

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.