AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Sources of Ultrafine Particles in the Atmosphere over the Eastern United States
LAURA POSNER, Spyros Pandis, Carnegie Mellon University
Abstract Number: 680 Working Group: Source Apportionment
Abstract Ultrafine particles can grow to become cloud condensation nuclei (CCN), playing a major role in the formation of clouds and climate change. Additionally, exposure to ultrafine particles has been linked to cardiovascular disease. Most chemical transport models (CTMs) explicitly simulate the mass concentrations of particles; ultrafine particles represent a minor fraction of this mass yet dominate number concentration. In this study, updated size distributions were introduced to the 3-D CTM PMCAMx-UF, which simultaneously simulates both mass and number size distributions of particles from 0.8 nanometers to 40 micrometers in diameter. The performance of the model in reproducing observed number concentrations in the Eastern U.S. is encouraging.
Source contribution simulations were completed by zeroing out approximately 90% of number emissions below a cutoff diameter specific to each source, which maintains larger particles and the corresponding surface and mass concentrations. The source contributions of gasoline, on- and off-road diesel, biomass, dust, and other emissions to particle number in the Eastern United States were quantified for a typical summertime period by running and analyzing a separate simulation for each source. Contributions of boundary conditions, initial conditions, and nucleation were also quantified in separate sensitivity tests. For Pittsburgh, PA, approximately 60% of the number of particles less than 50 nanometers in diameter were found to come from nucleation, while other sources contributed 13%, gasoline 12%, off-road diesel 7%, and on-road diesel 4%. Source contribution to particle number concentrations was found to vary greatly in space in time.