Characterization of Organics in Cloud Water: Measurements from the Present Day and from Decades Past

An emerging trend of increasing water soluble organic carbon (WSOC) has been observed in cloud water over the past decade at Whiteface Mountain (WFM) in Upstate New York. This trend is correlated with a growing inorganic ion imbalance and a growing fraction of ammonium, which in recent years has begun to surpass sulfate and nitrate combined. Altogether, these independent observations suggest that uncharacterized anions, which now make up a significant fraction of the cloud water composition in the northeastern U.S., are comprised of organic compounds. The driving factors behind such a striking increase in cloud water WSOC and potential impacts on secondary organic aerosol mass loadings are not clear, highlighting a need to better characterize the chemical makeup of the organic constituents in cloud water. Low molecular weight organic acids have now been added to the routine suite of cloud water chemical measurements at WFM, and we report on our first year of organic acid observations. While including eight organic acids that are typically found to be most abundant does significantly improve the anion deficiency, on average 28% of the anions remain uncharacterized. The organic component is further characterized using a high resolution time-of-flight aerosol mass spectrometer. Comparisons of recent and historical organic observations at WFM are presented. Lastly, cloud water samples of interest were analyzed for carbohydrates, often used as tracers for biomass burning events.