Overview of the CPOC Pilot Study at Whiteface Mountain, NY: Cloud Processing of Organics within Clouds (CPOC)

Abstract

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.

Investigating the evolution of water-soluble organic carbon in evaporating cloud water

“…47 As discussed previously, airmasses at WFM are expected to be predominantly inuenced by biogenic emissions. 20 In addition, a number of studies have also established that WSOC is efficiently produced from biogenic sources, at least in summertime in the eastern United States, when the cloud water samples were collected. [50][51][52] These results demonstrate that a small but signicant fraction of WSOC in clouds derives from organic gases reversibly partitioned to water.…”

“…Even when the site conducting aerosol sampling is downwind of the summit, there can be difficulties directly connecting the CW and the aerosol composition measurements due to droplet deposition. 15,20 Thus, the values of the blue crosses in Fig. 5 have a high level of uncertainty and would be biased low if deposition removed organics during transport from the summit to the downwind site.…”

“…16 WFM is mostly affected by airmasses transported from the western and central Unites States, Great Lakes region and Canada, suggesting the organics (gas and aerosol) are aged and oen dominated by contributions derived from precursor biogenic species. [17][18][19][20] Aged biomass burning smoke intercepts the summit of WFM and episodically inuences cloud water composition. 20,21 The Atmospheric Sciences Research Center (ASRC) at the University at Albany, Albany, NY, operates a research observatory at the summit, where cloud water sampling has been conducted regularly since 1994, historically focusing on acid deposition.…”

“…[17][18][19][20] Aged biomass burning smoke intercepts the summit of WFM and episodically inuences cloud water composition. 20,21 The Atmospheric Sciences Research Center (ASRC) at the University at Albany, Albany, NY, operates a research observatory at the summit, where cloud water sampling has been conducted regularly since 1994, historically focusing on acid deposition. 17 The cloud water sampling is usually conducted in summertime (June-September) due to prohibitive wintertime weather, while gas phase measurements are performed year round.…”

Insights into tropical cloud chemistry in Réunion (Indian Ocean): results from the BIO-MAÏDO campaign

“…Some well-established measurement observatories located at high altitudes have been carried out in numerous studies on cloud chemical composition, such as the Puy de Dôme (PUY) observatory in France (Bianco et al, 2017;Deguillaume et al, 2014;Renard et al, 2020;Vaïtilingom et al, 2013;Wang et al, 2020), the Schmücke Mountain in Germany (Brüggemann et al, 2005;Herrmann et al, 2005;Roth et al, 2016;Whalley et al, 2015), East Peak in Puerto Rico (Gioda et al, 2013), Mount Tai in China (Li et al, 2017;X. H. Liu et al, 2012;Shen et al, 2012), Whiteface Mountain in New York (Aleksic et al, 2009;Dukett et al, 2011;Lance et al, 2020), Great Dun Fell in England (Choularton et al, 1997), Kleiner Feldberg in Germany (Fuzzi et al, 1994;Wobrock et al, 1994), the Po Valley (Brege et al, 2018;Gilardoni et al, 2014), and Tai Mo Shan in Hong Kong SAR (Li et al, 2020). Nevertheless, most of the aforementioned observatories are located in the mid-northern latitudes with significant influence of continental emissions from natural and anthropogenic origins.…”