A global view of aerosol in the remote atmosphere from in-situ measurements on the NASA Atmospheric Tomography Mission - ICAS external seminar

Institute for Climate and Atmospheric Science. Speaker Christina Willamson, NOAA

Abstract: Aerosols nucleated in the free troposphere may account for 35% of cloud condensation nuclei (CCN) in global low-level clouds, yet the relative importance of different particle formation mechanisms remains poorly understood . The spatial distribution, concentration and fate of newly formed particles is controlled by nucleation mechanisms, availability of condensable vapors, and coagulation and condensation sinks. Constraining these factors in models is particularly important for pre-industrial aerosol-climate interactions, where the effect of newly formed particles on climate is amplified compared with the present day.

We present in-situ measurements of the global distribution of newly formed particles and coagulation and condensation sinks from the NASA Atmospheric Tomography Mission (ATom). Flights covered the Pacific and Atlantic basins from ~80°N to ~86°S latitude, constantly profiling between 0.2 and ~13km altitude over different seasons. The DC-8 aircraft was equipped with instrumentation for measuring various aerosol properties as well as greenhouse, reactive and trace gases. We compare these measurements with output from several global models with online aerosol microphysics.

Our measurements reveal a pattern of high nucleation mode aerosol concentrations at altitudes > 9 km over the tropics, coincident with convective influence and low coagulation sinks. Size distributions over this region show a continuous increase in modal diameter with decreasing altitude between the upper troposphere and top of the boundary layer, demonstrating that these particles grow to CCN sizes and can influence planetary albedo and radiation balance in the remote atmosphere. This process spans from ~30°S to ~30°N, representing half of the Earth's global oceanic surface area, and persists through seasonal changes.

We assess how this process is represented in each of the models, and use the models’ output to examine the roles of sinks, nucleation mechanisms and availability of condensable vapors in the formation and growth of these particles.

Christina Williamson1,2, Agnieszka Kupc1,2,3, Jack Kodros4, Anna L. Hodshire4, Jeffrey R. Pierce4, Pengfei Yu1,2, Fangqun Yu5, Gan Luo5, Eric Ray1,2, Bernadett Weinzierl3, Maximilian Dollner3, T. Paul Bui6, Karl Froyd1,2, Frank Erdesz1,2, Mathews Richardson1,2, and Charles A. Brock1

1NOAA Earth System Research Laboratory, Boulder, CO, USA

2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA

3Faculty of Physics, University of Vienna, Austria

4Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA

5Atmospheric Sciences Research Center, State University of New York, Albany, NY, USA

6NASA Ames Research Center, Moffett Field, CA, USA

Biography: Christina Williamson is a Research Scientist with CU Boulder’s Cooperative Institute for Research in Environmental Science in NOAA ESRL’s Chemical Sciences Division. Her research focuses on in-situ measurements of the microphysical properties of atmospheric aerosol, with special focus on new particle formation and its influence on the pre-industrial atmosphere. Christina has an undergraduate masters’ in Physics from Oxford University and completed her PhD at the Goethe University of Frankfurt am Main. Her doctoral work focused on understanding aerosol formation in the highly controlled environment of the CLOUD chamber at CERN, where she studied how different precursor gases and charge states affect how fast particles can form and grow. At NOAA she has been measuring aerosol microphysical properties on the NASA Atmospheric Tomography Mission. She is looking at how spatiotemporal variations of nano-aerosol size distributions inform our understanding of the global importance of new particle formation in affecting cloud properties, and uses these measurements to constrain formation, processing and transportation of aerosol in chemistry-climate models.

The seminar will be followed by cake and coffee in the School foyer.