Construction and Characterization of an Indoor Smog Chamber for the Measurement of the Optical and Physicochemical Properties of Aging Biomass Burning Aerosols Native to sub-Saharan Africa

Abstract. We describe here the construction and characterization of a new smog chamber facility (NCAT chamber) for studying the chemical and optical properties of biomass burning (BB) aerosols from biomass fuels native to sub-Saharan Africa. This facility is comprised of a ~9 m³ fluorinated ethylene propylene film (FEP) reactor placed in a temperature-controlled room and coupled with a cavity ring-down spectrometer, nephelometer, condensation particle counter, differential mobility analyzer and other analytical instruments, such as NO_X and O₃ analyzers, a GC, a filter sampler, and an impinger for collecting particles in water. Construction details and characterization experiments are described, including measurements of BB particulate size distribution and deposition rate, gas wall loss rates, dilution rate, light intensity, mixing speed, temperature and humidity variations, and air purification method. The wall loss rates for NO, NO₂, and O₃ were found to be (7.40 ± 0.01) × 10⁻⁴, (3.47 ± 0.01) × 10⁻⁴, and (5.90 ± 0.08) × 10⁻⁴ min⁻¹ respectively. The NO₂ photolysis rate constant was 0.165 ±0.005 min⁻⁴, which corresponds to a flux of (7.72 ± 0.25) × 1017 photons•nm•cm⁻²•s⁻¹ from 296.0−516.8 nm. Particle deposition rate was found to be (2.46 ± 0.11) × 10⁻³ min⁻¹ for pine at D_p = 100 nm. After initial mixing in the chamber, with the ultraviolet (UV) light off, the particle size distribution for BB samples used for the initial work did not stabilize until ~7.5 hours after injection peaking near a mobility diameter of ~340 nm. The chamber demonstrated gas and particle loss rates, and other properties comparable to other similar indoor smog chambers.