(682f) Boundary Layer Interactions with Ultrafine Aerosol | AIChE

(682f) Boundary Layer Interactions with Ultrafine Aerosol


Pettibone, A. - Presenter, University of Iowa
Eichinger, W. - Presenter, University of Iowa
Stanier, C. - Presenter, University of Iowa

Field measurements and collocated balloon and LIDAR measurements show pronounced diurnal patterns where new particle formation and growth is often seen at the time of ventilation of the stable nocturnal surface layer. For example, in the March 2006 MILAGRO campaign in Mexico City, observations at the T0 location could often be characterized by morning conditions with high particle mass concentrations, low mixing heights, and good correlation between particle number and carbon dioxide, indicative that particle number is controlled by primary emissions. In the afternoon, the CO2 level drops during ventilation of the daily polluted layer, and the coupling between CO2 and particle number breaks down, with particle number sometimes increasing as CO2 decreases. New particle formation events were observed both simultaneous to and separately from the afternoon ventilation. Simultaneous particle and mixed layer height measurements from Eastern Iowa also show a tight correlation in time between new particle formation events and boundary layer mixing. The use of rapid afternoon ventilation of the polluted layer to infer semivolatility of primary emissions is also discussed. We calculate size-resolved emission factors for Mexico City using a novel analysis method that uses the relative areas of short term elevations in CO2 and particle number to derive emission factors. Using this correlation between particle number and carbon dioxide, an average number based-emission factor of 3.4 x 10^(13) #/vehicle-km has been determined.