Oxalic acid does not have any known gas phase sources, but is there is considerable evidence of its formation within cloud droplets. Using the same gas+aqueous box model, we see considerable cloud production of oxalic acid, with the organic gas glyoxal serving as a key precursor

It is possible that cloud chemistry is one of the missing sources. We then employ a simple gas+aqueous chemistry box model at the summit of WFM to see if aqueous chemistry is a plausible missing source. However, there is no change in CH3COOH concentrations, and HCOOH is actually removed faster!

Isoprene and oxidation products were key sources for both HCOOH and CH3COOH according to the chemical box modeling. However, when comparing model results to gas phase estimates based on WFM cloud water, both organic acids where underestimated by ~10x, suggesting missing chemical sources

The airmass that impacted Whiteface Mountain (WFM) originated from central Missouri, a region of high biogenic VOC emissions like isoprene, and likely experienced influence of anthropogenic NOx emissions from the Chicago Metro area

As these acids grow in importance, it is critical we understand the chemistry that controls them. For this study, we use a combination of WRF-Chem and Lagrangian chemical box modeling to simulate unusually high concentrations of organic acids measured in Whiteface cloud water on July 1-2, 2018

Organic acids like formic (HCOOH), acetic (CH3COOH) or oxalic acid are among the most commonly found organic acids in the atmosphere. They can be an important source of acidity in clouds and rain, especially as many parts of the world reduce their sulfur emissions, but their chemistry is complex