Observed below-cloud and cloud interstitial submicron aerosol chemical and physical properties at Whiteface Mountain, New York during August 2017

A pilot study took place at Whiteface Mountain (WFM) in the Adirondacks of upstate New York during the summer of 2017 to evaluate the chemical processing of aerosol within clouds. Below-cloud and cloud interstitial submicron aerosols were characterized in real-time using an Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and other instruments deployed via the Atmospheric Sciences Research Center (ASRC) sprinter van mobile laboratory. The primary observation is a dominance of organic aerosol mass, averaging 66%–78% of PM2.5 during urban-influenced periods and 83–93% during biogenic-influenced periods, in stark contrast to observations in the northeastern U.S. in past decades when sulfate dominated the aerosol mass. The observations also show chemical differences between the below-cloud layer, the transition layer (just below-cloud), and the in-cloud layer. Comparison between these layers revealed enhanced inorganic nitrate in interstitial aerosol sampled in the transition and...