New Particle Formation Observed Under the Sulfur Plume Influence in the North American Forests During the CABINEX-2009 Campaign

Vijay Kanawade(1), Mark Erupe(1), Shan-Hu Lee(1),Barry Lefer(2),Xianliang Zhou(3),Thomas Jobson(4)

(1)Department of Chemistry, Kent State University, Ohio, (2)University of Houston, (3)State University of New York, Albany, (4)Washington State University

     Abstract Number: 570
     Last modified: May 13, 2010

Abstract
New particles produced over forests may affect climate by acting as CCN, but the chemical species involved in new particle formation (NPF) in forests remain an open question. This is in part due to the limited number of studies that simultaneously measure aerosol sizes and gas-phase precursors, such as H2SO4, NH3 and organic compounds. Simultaneous measurements of H2SO4, NH3, SO2, NOx, VOCs and particle size distributions were performed at the University of Michigan Biological Station (UMBS) to investigate particle nucleation and growth processes during the Program for Research on Oxidants: PHotochemistry, Emissions, and Transport (PROPHET) Community Atmosphere-Biosphere INteractions (CABINEX)-2009 campaign.

There were two strong NPF events (July 16th and August 2nd) during the 5 weeks of measurement period. Our analysis shows that NPF in the remote Michigan forests is closely tied to the sulfur plume, originated from power plants. Because of low pre-existing aerosol densities, formation of H2SO4 from SO2 oxidation by OH rapidly initiates particle nucleation. A good correlation between SO2 and NOx was also observed. The measured rates were proportional to [H2SO4] with a power of 1.86, suggesting the critical clusters for nucleation contain two H2SO4 molecules, although it is possible that other condensable species are also involved in the formation and subsequent growth of the critical clusters. There was a fairly good correlation between new particles and NH3. But, it is unclear how biogenically emitted VOCs (e.g, isoprene and its oxidation products) contribute to the aerosol formation and growth. Such infrequent NPF events seen in the Michigan forests during the summer with abundant VOCs led us to a novel question: why does NPF not occur in these remote forests?