Abstract. 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 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.
Supplementary material to "Tropospheric sources and sinks of gas-phase acids in the Colorado Front Range"
