Environmental Aerosol Chamber

 

Environmental Aerosol Chamber

        Schematic of the environmental aerosol chamber used to measure optical properties and heterogeneous reaction kinetics under dark and solar simulator conditions of mineral dust aerosol. The instrumentation associated with the environmental chamber includes a solar simulator (SS), water filter (WF), borofloat 33 glass window (UVT), water bubbler (V), flow meters (B), relative humidity sensors (RH), sampling mass spectrometer (QMS), pressure transducers (PT), pressure readout (P), thermocouples (TC), temperature readout (T), FT-IR spectrophotometer (FT-IR), mirrors for the external beam path (M), midband HgCdTe IR detector (MCT) , purge boxes for the external beam path (PB), UV/visible lamp source (L), fiber optic connector (FO), fiber optic collimators (C), spectrograph (S), and aerosol inlet valve and antechamber (A).

Solar simulator spectral irradiance at the bottom of the environmental aerosol chamber. The insert shows the solar constant profile in the environmental aerosol chamber.

The environmental aerosol chamber has been designed to be used for kinetic measurements of heterogeneous reactions involving mineral dust aerosol. The chamber has a total volume of 151 L and a surface-to-volume ratio 10.7 m-1. A schematic of the chamber is shown in A. All of the interior surfaces are coated with a layer of Teflon to minimize wall reactions. A solar simulator has been cooperated to the chamber for studies of heterogeneous photochemical reactions that occur during “daytime” mineral dust aerosol chemistry. The spectral irradiance of the solar simulator is shown in B with insert showing the solar constant profile. 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. Aerosol and gas-phase concentrations are typically adjusted to yield a time scale for reaction that is compatible with the sensitivity and time resolution of the probe method. We have successfully applied the chamber for studies under both dark and irradiated conditions at various relative humidities to simulate the humid environments found in the atmosphere. Recently for reactions of ozone decomposition on components of mineral dust aerosol, a kinetic model was also built to simulate reactions in the chamber to extract valuable kinetic data. 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, in future studies, the environmental aerosol chamber will 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.