Chemical Processing of Organics within Clouds (CPOC): 2017 Pilot Study at Whiteface Mountain

Aqueous chemical processing within cloud and fog water has been identified as a key process in the formation of secondary organic aerosol mass, which is found abundantly throughout the troposphere. Yet, significant uncertainty remains regarding the organic chemical reactions taking place within clouds and the conditions under which those reactions occur. Routine longterm measurements from the Whiteface Mountain (WFM) Research Observatory in upstate NY provide a unique and broad view of regional air quality relevant to the formation of particulate matter within clouds, largely due to the fact that the summit of WFM is within non-precipitating clouds 30-50% in summertime and the site is unperturbed by local sources. This talk will highlight the experimental design and preliminary observations from an NSF-funded pilot study that took place at WFM in August 2017 targeting the Chemical Processing of Organics within Clouds (CPOC). During the CPOC study, upwind below-cloud measurements of aerosol CCN activation efficiency, size distribution and chemical composition measured with a high resolution time of flight aerosol mass spectrometer are compared with a subset of the same measurements made at the summit. Under certain conditions, aerosols measured at the summit “between clouds” have been detrained from shallow cumulus recently intercepting the summit and therefore may be considered “cloud processed”. Wind LIDAR and radiosonde observations are used to link the below-cloud and summit observations. These pre- and post- “cloud processed” aerosols are compared with the chemical composition of cloud water samples to evaluate changes to the organic partitioning in the aqueous and aerosol phases.