Photochemistry of Aerosol Particles

Aerosol particles are increasingly recognized as important components of the lower atmosphere because of their effect on atmospheric chemistry, climate, and air quality.  As a part of the AirUCI research program, we are investigating photochemistry that occurs inside and at the surface of aerosol particles.  These include both organic and inorganic particles.

In the Nizkorodov group, a key question is the significance of surface vs. bulk reactions in the chemistry and photochemistry of organic aerosols.  We have recently constructed a powerful aerosol particle mass spectrometer that relies on laser heating of particles and chemical ionization detection of the vaporized molecules.

In a typical application of this technique, the mass spectrometer is used to analyze the surface products of a laboratory-generated organic aerosol after its reaction with typical atmospheric oxidizers and/or UV radiation.

Schematic diagram of the aerosol particle chemical ionization mass spectrometer.

AirUCI postdoctoral researcher Ao Lin (left) and graduate students Xiang Pan (right)
and Anthony Gomez (back) align the aerosol particle mass-spectrometer.

The Nizkorodov group also carries out infrared cavity ring down spectroscopy studies of gas phase oxidation products of organic films on surfaces.  For example, they measured HCHO from the ozone oxidation of alkene-terminated SAMs on silica surfaces and were able to put an upper limit on the production of HCOOH in this reaction.

Schematic diagram of the infrared cavity ring down apparatus.

In the Phillips laboratory at the University of Canterbury in Christchurch, New Zealand, aerosol photochemistry is studied using a custom-built chamber designed for studies of photochemical and photocatalytic reactions in aerosols.  Aerosol size is monitored using an aerodynamic particle sizer, gas phase species are followed using mass spectrometry, and the liquid phase is analyzed using FTIR.