Kinetic measurements of heterogeneous reactions involving mineral dust can also be made using an environmental aerosol reaction chamber. A schematic of the chamber is shown below. All of the interior surfaces are coated with a layer of Teflon to minimize wall reactions. In these studies, a powder sample is suspended in a chamber and mixed with the reactive gas of interest in a humidity controlled, atmospheric pressure environment. Subsequent chemistry is monitored by FT-IR and UV/Vis absorption spectroscopy, and/or a fast-sampling quadrupole mass spectrometer. More sensitive laser-based probe techniques can also be developed and applied, when appropriate. The aerosol and gas concentration will be adjusted to yield a time scale for reaction that is compatible with the sensitivity and time resolution of the probe method. Recent FT-IR experiments have shown that this chamber is well suited for competition studies where the gas phase has multiple components (e.g. H₂O, CO₂, SO₂ and HNO₃)via automated spectral subtraction of water and CO₂ bands and the loss of SO₂ or HNO₃ can be followed. The chamber is also being used to measure the optical constants of mineral dust aerosol in the IR and UV/Vis portions of the electromagnetic spectrum. Most importantly, the chamber can be used to measure changes in the optical constants as the mineral dust is being chemically processed (similar what happens as the particles are “aged” in the atmosphere). An aerodynamic particle sizer is used in conjunction with the environmental aerosol chamber for sizing measurements.

 

 

Schematic of the 151 liter environmental aerosol reaction chamber used to measure heterogeneous reaction kinetics and optical constants of mineral dust aerosol.