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Fall 2001

Formation and Growth of Nanoparticles in the Atmosphere

by

Peter H. McMurry
Professor and Head
Mechanical Engineering Department

University of Minnesota, Minneapolis, MN 55455

Wednesday, September 12, 2001
3:30-4:30 p.m.
Room 108 ME
Broadcast on UNITE Channel A
Coffee and cookies will be available in 152 ME following the seminar

The formation of new atmospheric particles by gas-to-particle conversion leads to enhanced concentrations of very small atmospheric particles. Such particles can serve as cloud condensation nuclei and thereby affect the earth's radiation balance, so understanding the physical-chemical processes that regulate particle formation rates is important for climate modeling. We have studied the formation and growth of new particles in the remote troposphere and in the urban Atlanta atmosphere. Key to this work are the development of instrumentation for measuring the size distributions of freshly formed 3 to 10 nm particles and our collaboration with Fred Eisele and coworkers at NCAR who measure gas phase precursors including sulfuric acid vapor and OH. We have found that at locations close to the surface particles tend to be formed at rates that greatly exceed those predicted by existing theories. Nucleation in the Atlanta troposphere is consistent with a collision-controlled process, in which the production of sulfuric acid vapor by reaction of SO2 with OH is the rate-controlling step. The enhanced particle production rates near the surface suggest that sulfuric acid nucleation rates are enhanced by the participation of additional species that reduce the nucleation barrier; ammonia is one likely candidate. This seminar will provide a summary of our atmospheric observations over the past decade and the implications of these observations for nucleation mechanisms. Measurements of nanoparticle composition that are planned for Atlanta in August 2002 will be discussed.

Peter H. McMurry has been on the faculty of the Mechanical Engineering Department since 1977 when he completed his doctoral research at Caltech. He has been Head of the Department of Mechanical Engineering Department since 1997. His research focuses on the chemistry and physics of gas borne particles, including the formation of contaminant particles in semiconductor processing equipment, the synthesis of nanophase materials in aerosol reactors, and properties and formation of atmospheric aerosols.

Informal Faculty Luncheon: Wednesday, September 12, 2001, 12:00 noon.

A table has been reserved at McCormick's Restaurant in the Radisson. Prof. McMurrry will be able to attend.