AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Sources of Ultrafine Particles in the Atmosphere over the Eastern United States
LAURA POSNER, Spyros Pandis, Carnegie Mellon University
Abstract Number: 493 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 US is encouraging.
Source contribution simulations were completed by zeroing out the emitted particles smaller than 150 nm, for only one source per simulation, but maintaining larger particles and the corresponding surface and mass concentrations. Contributions of boundary conditions, initial conditions, and nucleation were also quantified in separate sensitivity tests. The source contributions of gasoline, on- and off-road diesel, natural gas, wood, biomass, dust, and other emissions to particle number in the Eastern United States were quantified for a typical summertime period. For Pittsburgh, PA, approximately 51% of the total number of particles is due to nucleation, while 29% comes from traffic emissions, 2% from power plants, and 18% from other sources, such as long-range transport. The results are consistent with observation-based estimates of the sources of ultrafine particles in Pittsburgh, though the contributions of the various sources and processes are highly variable in space and time.