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

James M. Mattila, Patrick Brophy, Jeffrey Kirkland, Samuel Hall, Kirk Ullmann, Emily V. Fischer, Steve Brown, Erin McDuffie, Alex Tevlin, Delphine K. Farmer
2018 Atmospheric Chemistry and Physics Discussions  
<p><strong>Abstract.</strong> 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
more » ... ces of HNO<sub>3</sub>, HNCO, formic, propionic, butyric, valeric, and pyruvic acid. Vertical profiles taken on the 300<span class="thinspace"></span>m tower demonstrate net surface-level emissions of alkanoic acids, but net surface deposition of HNO<sub>3</sub> and pyruvic acid. The surface-level alkanoic acid source persists through both day and night, and is thus not solely photochemical. Reactions between O<sub>3</sub> 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 acid, and likely contribute photochemical precursors to HNO<sub>3</sub> 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>
doi:10.5194/acp-2018-326 fatcat:bl6gdjnzarcrbckwt7fie6jzgm