1C: Whiteface Mountain Coordinated Cloud Chemistry Investigation

In September 2016, over 40 scientists from Canada, Germany, and the United States developed a plan at the Whiteface Mountain Cloud Chemistry Workshop (https://www2.acom.ucar.edu/cloud-chemistry/whiteface-mountain-cloud-chemistry-study) for a coordinated effort in investigating cloud chemistry at the Whiteface Mountain Observatory in upstate New York. A three-prong strategy is being pursued, conducting a small-scale pilot study, analyzing cloud water samples, and conducting a model intercomparison of cloud chemistry.

The small-scale pilot study, Chemical Processing of Organics within Clouds (CPOC), was conducted August 11-25, 2017 by ASRC, U. Albany at Whiteface Mountain to characterize typical cloud properties, and trace gas and aerosol composition, and to inform planning of future field intensive operations. More information can be found at https://www.asrc-research.com/cpoc

After the September 2016 workshop, cloud water samples from three cloud events in 2016 were distributed to several laboratories to perform a comprehensive chemical and biological analysis of the cloud water composition. The analyses are currently being performed and results are being collected at the Whiteface Mountain Cloud Chemistry website (https://www2.acom.ucar.edu/cloud-chemistry).

Modeling studies of the cloud chemistry at Whiteface Mountain include regional-scale models (e.g. WRF-Chem and WRF-CMAQ) and box modeling. Most of the effort has been focused on the box model intercomparison.  This intercomparison uses liquid water content, temperature, pressure, and water vapor measurements from one of the 2016 Whiteface Mountain cloud events being analyzed. Four simulations have thus far been performed, including a clear sky simulation, and cloudy simulations with set liquid water content and pH, and with variable liquid water content and pH. Five groups (TROPOS in Leipzig, Germany, LaMP in Clermont-Ferrand, France, Columbia University, NOAA/ESRL/CSD, and NCAR/ACOM) are participating in the intercomparison. Early results (Figure 1) show substantial variation among models for the key oxidants OH and HO2. In the aqueous phase, reactions involving the OH radical are the primary production pathway of organic acids that can form secondary organic aerosols when cloud drops evaporate. Because of the wide variation in OH predictions, the different models also predict a wide variation in organic acid formation (Figure 1). Currently the results are being analyzed to determine causes of the model diversity.

Ultimately the Whiteface Mountain Coordinated Cloud Chemistry Investigation hopes to conduct an intensive, community-wide field study at the mountaintop. The current activities (pilot study, comprehensive cloud water chemical analysis, and model studies) will provide guidance to designing the field study. It is anticipated that the intensive field study will occur in summer 2019 or 2020.

Figure 1. Box model results from five different models
Figure 1. Box model results from five different models for aqueous-phase concentrations of hydroxyl radical (OH), hydroperoxy radical (HO2), formic acid (HCOOH), acetic acid (CH3COOH), glycolic acid, and glyoxylic acid. Blue lines are from box model by Barth (NCAR/ACOM), red lines from McNeill (Columbia Univ.), gold lines from CLEPS model (LaMP, Clermont-Ferrand, France), green lines from TROPOS model (Leipzig, Germany), and magenta lines from Ervens (NOAA/ESRL/CSD). Cloud occurred from 1800 LT to 1400 LT (hour 38). Daytime and nighttime are marked with the blue and black boxes, respectively.

Reference:

Mary Barth (ACOM/MMM), Annmarie Carlton (University California – Irvine), Sara Lance (Atmospheric Sciences Research Center, University at Albany, SUNY), Hartmut Herrmann and Andreas Tilgner (TROPOS, Leipzig, Germany), V. Faye McNeill (Columbia University), Barbara Ervens (NOAA/ESRL/CSD, Boulder, CO), and Laurent Deguillaume (LaMP/OPGC, University Blaise Pascal, Clermont-Ferrand, France)