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

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 m 3 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 O 3 20 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, NO 2 , and O 3 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 NO 2 photolysis rate constant was 0.165 ±0.005 min -1 , 25 which corresponds to a flux of (7.72 ± 0.25) × 10 17 photons•nm•cm −2 •s −1 from 296.0−516.8 nm. Particle deposition rate was found to be (2.46 ± 0.11) x 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 30

Refractive Indices of Biomass Burning Aerosols Obtained from African Biomass Fuels Using RDG Approximation

“…Details of the experimental approach and the error analysis are described in our earlier work [49,50]. Details of the smog chamber and the production of BB aerosol are described in [51], and we only provide a brief description here.…”

“…For laboratory samples, BB aerosols were generated by combusting each wood sample in a tube furnace. The furnace (Carbolite Gero, HST120300-120SN) holds an 85 mm outer diameter (OD), 80 mm inner diameter (ID, and 750 mm long quartz working tube, and has a heated region of 300 mm as described in Smith et al [51]. Stainless steel mounts and insulation plugs on either end enable the introduction and sampling of gasses.…”

“…The smoke and gasses produced from combustion were sent directly to the chamber via a heated (200 • C), 1 4 -inch OD stainless steel transfer tube. The characteristics of the smog chamber used in this work are described in Smith et al [51]. BB particles were taken from the smog chamber via graphite impregnated silicone tubing before entering a 710 nm impactor inlet (3.8 µm diameter cut point), neutralizer, and long differential mobility analyzer (DMA, TSI, Model 3080), where the aerosol was size selected.…”