Many of us think of spray cans when we hear the word aerosol, but we think of aerosol as particles suspended in air. Aerosol is a system that includes both particles and the air in which they are suspended; we treat this as a system because typically molecules move constantly from the air into particles and vice versa. We need to understand the behavior of both gases and particles in order to understand atmospheric aerosol, so in the Ultrafine Aerosol Research Group (“UA Group”) we focus on measuring both. Why do we care about atmospheric aerosol? Particles suspended in the air are the main constituent of the haze that we perceive as smog. They can impact human health through afflictions like asthma, bronchitis, as well as climate by directly scattering sunlight and modifying cloud properties.


The main goals of the UA Group are to understand the chemical species and mechanisms by which ultrafine aerosol particles form and grow in the atmosphere. Specific questions include:

  • What possible roles do organic compounds play in the formation of the stable clusters and for the growth of these clusters into “new particles”?
  • Are the compounds responsible for the birth and growth of aerosol particles formed in the atmosphere or within the particles themselves?

Another interest that we have is in the impacts of ultrafine aerosol. Particles of this size form the inner “seed” upon which water may condense to form cloud and fog droplets. When we change the composition of ultrafine aerosols through the pollutants we emit, we may be impacting cloud droplet formation, which in turn could affect the amount of sunlight we receive as well as precipitation.

To study these phenomena, the UA Group has teamed with university investigators to develop a unique set of instruments. Among these is the Thermal Desorption Chemical Ionization Mass Spectrometer, or TDCIMS, which can characterize the chemical composition of particles as small as 5 nm.