HR: 15:10h
AN: A43E-07    [Abstracts]
TI: Aerosol Nucleation Frequency and Hygroscopicity at a Forested Site in the Southeastern United States
AU: * O'Halloran, T L
EM: ohalloran@virginia.edu
AF: Department of Environmental Sciences, University of Virginia, Clark Hall, UVA, Charlottesiville, VA 22904, United States
AU: Fuentes, J D
EM: jf6s@virginia.edu
AF: Department of Environmental Sciences, University of Virginia, Clark Hall, UVA, Charlottesiville, VA 22904, United States
AU: Collins, D R
EM: dcollins@tamu.edu
AF: Department of Atmospheric Sciences, Texas A&M University, 3150 TAMU, College Station, TX 77843, United States
AU: Cleveland, M J
EM: mjc4v@virginia.edu
AF: Department of Earth Sciences, University of New Hampsire, 121 James Hall, Durham, NH 03824, United States
AB: This paper examines how aerosol hygroscopicity and nucleation frequency, measured with a tandem differential mobility analyzer (TDMA) at a rural site in the southeastern United States, vary with air mass source regions and transport pathways. We also examine an observed enhancement in aerosol hygroscopicity during nucleation events. During October through December, 2006, a TDMA was used to measure submicron aerosol size distributions and size-resolved hygroscopicity at a forested site in the southeastern U.S. Measurements were conducted above a mixed deciduous forest at the Virginia Forest Research Facility, a newly operational permanent micrometeorological facility located approximately 20 km east of the foothills of the Blue Ridge Mountains. The site features a 40-m walkup scaffolding tower above a 20-m mixed deciduous forest with excellent fetch, and a climate controlled lab for housing instruments and data acquisition systems. Hygroscopic growth factor distributions were measured for eight dry diameters between 0.013 and 0.400 μm. Cluster analysis of back trajectories was applied to identify characteristic source regions and air mass pathways during the study period. Significant differences were found in the frequency of aerosol nucleation events and hygroscopicity amongst the five distinct pathways identified by the cluster analysis. Nucleation occurred most frequently when fast moving air masses originated from the northern central U.S. and lower central Canada. In these cases existing aerosol surface area was low, and the majority of trajectories passed directly over the Ohio River valley. Hygroscopicity generally increased with increasing dry diameter, except for the largest size bin, which had a slightly lower hygroscopicity than the next smallest size. Two clusters with short, stagnant trajectories contained aerosols with enhanced hygroscopicity at dry diameters less than 0.100 μm. Aerosol hygroscopicity was significantly enhanced, especially at small diameters, during new particle formation events.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting