AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Chemistry of New Particle Growth Events in Mixed Biogenic and Urban Emissions - Results from the CARES 2010 Campaign
QI ZHANG, Ari Setyan, Maik Merkel, Berk Knighton, Cody Floerchinger, Scott Herndon, Timothy Onasch, Douglas Worsnop, Chen Song, John Shilling, Univeristy of California, Davis
Abstract Number: 565 Working Group: Aerosol Chemistry
Abstract New particle formation and growth events were frequently observed over the Sacramento and western Sierra Foothills area in June 2010 during the Carbonaceous Aerosols and Radiative Effect Study (CARES). Using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) we investigated the evolution of the size-resolved chemical composition of new particles at the T1 site of CARES about 40 km northeast of Sacramento. The new particle events usually occurred in the morning with the appearance of an ultrafine mode centered at 10-15 nm (in mobility diameter, Dm) followed by the growth of this mode to ~ 50 nm in the afternoon. The events were generally associated with southwesterly winds which bring urban plumes from Sacramento and the San Francisco Bay Area to the T1 site. Our results indicate that the growth of new particles was driven primarily by the condensation of oxygenated organic species and, to a lesser extent, ammonium sulfate. The average increase of organic mass in the ultrafine particles during this period was approximately 7.5 times higher than that of sulfate. The chemical composition of organics in ultrafine mode during the growth events was very similar to that of anthropogenically-influenced secondary OA (SOA) identified in urban plumes. In addition, the concentrations of species representative of urban emissions (e.g., black carbon, CO and toluene) were on average 1.5 times higher during the new particle event days than during the non-event days, so were the concentrations of the photo-oxidation products of biogenic VOCs. These results indicate that the frequent new particle formation and growth events over the Sacramento and Sierra-Nevada regions were promoted by the interaction between biogenic emissions and transported urban plumes.