Peter McMurry
Particle Technology Laboratory
Department of Mechanical Engineering
University of Minnesota
111 Church St. SE
Minneapolis, MN 55455
612-624-2817
fax 612-626-1854
McMurry@me.umn.edu

F. L. Eisele
National Center for Atmospheric Research

R. Weber
Georgia Institute of Technology

This project involves research on the nucleation and growth of atmospheric aerosols. The proposed research involves the development and refinement of two techniques for measuring the composition and properties of freshly nucleated sub-10 nm particles including: (1) the selected ion chemical ionization mass spectrometer (SICIMS) method for measuring the composition of sub-10 nm particles, and (2) the nano-tandem differential mobility analyzer (nano-TDMA) for measuring size-dependent water uptake and volatility of 3-10 nm particles. We are using the SICIMS and nano-TDMA methods for 3 to 10 nm particles, along with measurements of H₂SO₄, OH, SO₂, NH₃, 3 nm to 2 µm size distributions, and semicontinuous (3 minute time resolution) measurements of fine particle sulfate and nitrate concentrations to study nucleation in the Atlanta atmosphere during August 2002.

The goal is to be able to predict rates at which particles are produced and subsequently grow. Our measurements will enable us to quantitatively test the validity of our hypothesis that nucleation in Atlanta is a collision-controlled process. Collision-controlled nucleation occurs when a condensable species produced by a gas phase reaction (the "monomer") collides with and sticks to other condensable molecules or molecular clusters much faster than it evaporates. Nucleation in any chemical system can occur at the collision-controlled limit if the rate of monomer production by gas phase reactions is sufficiently high (or its vapor pressure sufficiently low). We hypothesize that production of H₂SO₄ by the SO2-OH reaction is the rate limiting step for nucleation in Atlanta, and our measurements will enable us to test these hypotheses and to measure the properties and behavior of the freshly nucleated aerosols.

Some further information can be found in the viewgraphs from a presentation at the Atmospheric Sciences Program Annual Meeting held in February 2001.