The UBC ATMOX chamber: An 8 m ³ LED-powered modular environmental chamber for indoor and outdoor atmospheric chemistry

Abstract. Environmental chambers are controlled reaction vessels used to investigate atmospheric processes such as photochemical smog, atmospheric fate of molecules and secondary organic aerosol formation. Environmental chambers are typically equipped with UV-A fluorescent lights with wavelengths between 350 and 410 nm or xenon lamps with wavelengths between 300 and 800 nm. However, these types of lights increase the temperature of the chamber, are energy intensive and are not tunable to specific wavelengths. Fluorescent lights are also becoming redundant in the light industry. To address these issues, we prototyped the use of light-emitting diode (LED) lights from Violumas on our 8 m3 environmental chamber for photochemical experiments to enable stratospheric, tropospheric and indoor light conditions. The University of British Columbia (UBC)'s Advanced Techniques for Mechanisms of OXidation (ATMOX) chamber was assembled with custom-made wide-angle LEDs of six different wavelengths from Violumas: 275, 310, 325, 340, 365, 385 nm. We also added LED grow plant lights (Feit Electric) for irradiance between 450 and 630 nm. The LEDs were wired to a potentiometer control panel to modulate their output on a per wavelength basis. We used a total of 1440 custom LEDs and 1320 commercial grow plant LEDs, costing USD$ 44,951 and USD$ 1,300, respectively. We demonstrate their energy efficiency, their ability to generate less heat, and their ability to generate wavelength-specific photochemical processes. Furthermore, chemical actinometry using NO2 enabled us to calculate a photolysis rate constant (JNOx) ranging from 2.28 × 10-4 to 4.93 × 10-3 s-1, which is nicely comparable to 4.50 × 10-3 s-1 in Vancouver, Canada during the summer solstice. In addition to the lights, the UBC ATMOX chamber was designed to be particularly modular. The chamber frame has 12 aluminum T-slot rails (2.66 × 2.66 × 3 m, 80/20 Rocky Mountain Motion Control), and a pulley system to enable the 8 m3 bag to collapse and inflate, to perform batch or continuous mode experiments. The Teflon chamber bag has sealable openings at each corner to allow access to the interior of the bad for regular thorough cleaning. Overall, our chamber is allowing us to study topics of current interest in atmospheric chemistry: from the fate of indoor air fragrances to cannabis emissions and from wildfire aerosol photochemical changes to the biogeochemical cycling of selenium.