Aqueous chemical processing within cloud and fog water is thought to be a key process in the production and transformation of secondary organic aerosol mass, found abundantly and ubiquitously throughout the troposphere. Yet, significant uncertainty remains regarding the organic chemical reactions taking place within clouds and the conditions under which those reactions occur, owing to the wide variety of organic compounds and their evolution under highly variable conditions when cycled through clouds. Continuous observations from a fixed remote site like Whiteface Mountain (WFM) in New York State and other mountaintop sites have been used to unravel complex multi-phase interactions in the past, particularly the conversion of gas-phase emissions of SO2 to sulfuric acid within cloud droplets in the presence of sunlight. These scientific insights led to successful control strategies that reduced aerosol sulfate and cloud water acidity substantially over the following decades. This paper provides an overview of observations obtained during a pilot study that took place at WFM in August 2017 aimed at obtaining a better understanding of Chemical Processing of Organic compounds within Clouds (CPOC). During the CPOC pilot study, aerosol cloud activation efficiency, particle size distribution and chemical composition measurements were obtained below-cloud for comparison to routine observations at WFM including cloud water composition and reactive trace gases. Additional instruments deployed for the CPOC pilot study included a doppler LiDAR, sun photometer and radiosondes, to assist in evaluating the meteorological context for the below-cloud and summit observations.

This content is only available as a PDF.


Current affiliation: Center for Environmental Studies, National Central University, Taiyuan, Taiwan.

Current affiliation: New York State Department of Environmental Conservation, Albany, NY.


Current affiliation: National Center for Atmospheric Research, Boulder, CO.

Current affiliation: San Jóse State University, San Jóse, CA.

Current affiliation: New York City Department of Environmental Protection, New York, NY.