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

Emma L Mungall,Daniel Kunkel,David W Tarasick,Christopher J Cox,Jeremy J B Wentzell,Jennifer G Murphy,Jonathan P D Abbatt,John Liggio,Taneil Uttal,Sangeeta Sharma,Gregory R Wentworth,Ellen Gute

doi:10.5194/acp-18-10237-2018

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.

Highlights

Formic acid (FA) and acetic acid (AA) are ubiquitous and abundant in the troposphere and are major contributors to cloud water acidity in remote regions (Paulot et al, 2011)
FA and AA have many different sources, the relative contributions of those sources depend on the location, and not every source will be relevant in every location
Enhanced wet deposition in the Arctic boundary layer in summer tends to reduce the atmospheric lifetime of scavengeable species such as FA and AA, making long-range transport less likely (Croft et al, 2016)

Summary

Introduction

Formic acid (FA) and acetic acid (AA) are ubiquitous and abundant in the troposphere and are major contributors to cloud water acidity in remote regions (Paulot et al, 2011). Cloud water serves as an important atmospheric chemical reactor (Lelieveld and Crutzen, 1991). As many chemical reactions depend strongly on pH, cloud water acidity is relevant to the formation of secondary organic aerosol as well as to the processing of other forms of atmospheric particulate matter (Ervens et al, 2011). FA and AA have been measured in a wide variety of environments, both urban and remote, from the poles to the Amazon to the largest cities in North America. FA and AA have many different sources, the relative contributions of those sources depend on the location, and not every source will be relevant in every location. The sources of FA and AA include secondary photochemical production from both anthropogenic and biogenic precursors (Yuan et al, 2015; Liggio et al, 2017); direct emissions from plants (Kesselmeier et al, 1998; Kuhn et al, 2002), soils (Sanhueza and Andreae, 1991), and biomass burning (Veres et al, 2010; Ito and Penner, 2004); direct emissions

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Conclusion