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

• Published in: Atmospheric Chemistry and Physics
• Main Authors: J. M. Mattila, P. Brophy, J. Kirkland, S. Hall, K. Ullmann, E. V. Fischer, S. Brown, E. McDuffie, A. Tevlin, D. K. Farmer
• Format: Article
• Language: English
• Published: Copernicus Publications 2018-08-01
• Online Access: https://www.atmos-chem-phys.net/18/12315/2018/acp-18-12315-2018.pdf
• ISSN: 1680-7316; 1680-7324

<p>We measured organic and inorganic gas-phase acids in the Front Range of Colorado to better understand their tropospheric sources and sinks using a high-resolution time-of-flight chemical ionization mass spectrometer. Measurements were conducted from 4 to 13 August 2014 at the Boulder Atmospheric Observatory during the Front Range Air Pollution and Photochemistry Éxperiment. Diurnal increases in mixing ratios are consistent with photochemical sources of HNO₃, HNCO, formic, propionic, butyric, valeric, and pyruvic acid. Vertical profiles taken on the 300&thinsp;m tower demonstrate net surface-level emissions of alkanoic acids, but net surface deposition of HNO₃ and pyruvic acid. The surface-level alkanoic acid source persists through both day and night, and is thus not solely photochemical. Reactions between O₃ and organic surfaces may contribute to the surface-level alkanoic acid source. Nearby traffic emissions and agricultural activity are a primary source of propionic, butyric, and valeric acids, and likely contribute photochemical precursors to HNO₃ and HNCO. The combined diel and vertical profiles of the alkanoic acids and HNCO are inconsistent with dry deposition and photochemical losses being the only sinks, suggesting additional loss mechanisms.</p>