Organic acids are numerous and pervasive in Earth’s lower atmosphere. They contribute to ozone formation chemistry as well as the production of secondary organic aerosols, thus impacting both human and ecosystem health. Despite their relevance, organic acid budgets in the atmosphere remain poorly understood. Models underestimate measured ambient concentrations of many organic acids, suggesting an underestimation of sources, an overestimation of sinks, or a combination of both. The limited available measurements of organic acid sources and sinks is a likely cause of model-measurement discrepancies, coupled to a bias towards summer field campaigns.
My research seeks to improve atmospheric models by directly measuring gaseous organic acid sources and sinks over a Colorado ponderosa pine forest. To this end, we deployed a Chemical Ionization Mass Spectrometer and a 3-dimensional sonic anemometer to make fast, sensitive measurements of organic acid vertical fluxes during five, seasonally representative campaigns as part of the Seasonal Particles in Forests Flux studY (SPiFFY). We observed seasonality in both mixing ratios and fluxes for formic, propionic, methacrylic, butyric, and valeric acids. Large upward fluxes of formic acid occurred during summer 2015, summer 2016, and fall 2016. Air temperature correlated exponentially with acid fluxes during each season. We aim to use these data to develop parameterizations that will improve models of organic acid biosphere-atmosphere exchange and subsequently improve our understanding of ozone and secondary organic aerosol budgets.