Impact of African Dust on Cloud Properties During ICE-T Using On-line Single Particle Mass Spectrometry

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This project involves deploying an Airborne Aerosol Time of Flight Mass Spectrometer (A-ATOFMS) aboard the NSF/NCAR C-130 research aircraft during the Ice in Clouds Experiment - Tropical Field Campaign (ICE-T) in the Caribbean region in July 2011. In situ atmospheric ice nucleus (IN) measurements will be made using single particle mass spectral signatures to determine the sources of ice nuclei within these clouds. The composition of aerosols feeding the clouds will be compared with those of cloud condensation nucleus (CCN) and IN residuals within clouds to determine which particle sources are enriched as IN. An additional ATOFMS will perform continuous aerosol measurements in a tropical montane cloud forest in Puerto Rico as part of a large ground-based study coordinated by the University of Puerto Rico. Measurements of aerosol size and composition, as well as of cloud water and precipitation chemistry, will be performed to obtain information on the variability of aerosol-cloud interactions in the region. Finally, controlled lab studies will measure the IN properties of mineral dust and terrestrial and marine-derived bioparticles. A primary goal of ICE-T is to show that under given conditions, direct ice nucleation measurement(s), along with measurements of individual particle chemistry and size, can be used to predict the number of ice particles formed by nucleation mechanisms in select clouds. The ground, aircraft, and lab studies aim to better understand the impacts of different sources on cloud properties and precipitation in the Caribbean region, including long range transported African Dust, biological particles, marine sea spray, and pollution.In-situ measurements of the composition and sources of IN coupled with other measurements of microphysics, meteorology, and thermodynamics will provide unprecedented insight into the cloud impacts from different sources of particles, with a particular focus on the role of dust and bioparticles in ice nucleation processes in warm (-15 degrees C) maritime clouds in a tropical region. The results will lead to a better understanding of how mineralogy and aging of dust from the largest source region in the world impacts clouds and precipitation in the Caribbean region, a highly under-studied region with sensitive ecosystems. Results from the studies will be used to constrain and improve models to better predict ice cloud formation on a global scale. Students will be trained across disciplines of chemistry, physics, modeling, atmospheric chemistry, and instrument development. These students will have the opportunity to interact with a broad range of scientists and students from multiple schools and organizations as part of ICE-T, as well as in the Puerto Rico and Virgin Island area. A web page focusing on these studies will be developed as well as a public exhibit at the Birch Aquarium focusing on ice clouds and how they form in the atmosphere and impact climate and weather. A mobile exhibit will be taken to local elementary schools to teach children about clouds and climate. University of Puerto Rico students will assist with measurements during the campaign as well as with subsequent analysis and integration of the results. Project results will be used to educate the public on how the aerosols chemistry can impact regional and global precipitation patterns and climate.