Not all boxes are equal: Investigation of parameters affecting PM2.5 particle removal by the Corsi-Rosenthal box

The Corsi-Rosenthal (C-R) box has gained widespread popularity as an affordable, do-it-yourself air cleaner designed to improve indoor air quality. Despite its rapid adoption, limited studies have evaluated how different operational and experimental variables affect the C-R box's efficiency. This study investigated the Clean Air Delivery Rate (CADR) of the C-R box as a function of filter rating, its electret enhancement, measurement interval, location, and type of measurement devices, and additional air mixing when removing PM 2.5 sodium chloride (NaCl) or Arizona Road Dust (ARD) particles in a 3024 ft 3 (∼86 m 3 ) room. Based on measurements by a research-grade MiniWRAS (1371, DURAG Group, Hamburg, Germany), the C-R box with four 2-inch MERV-13 filters achieved a CADR of 358.56 ± 10.58 cubic feet per minute (cfm) at its highest fan speed, outperforming MERV-8 filters (209.93 ± 9.30 cfm) by 71 % despite only a 41 % increase in filter cost. MERV-13 filters with an electret designation did not improve CADR compared to plain MERV-13 filters. When challenged with ARD particles, the C-R box achieved a CADR of 416.60 ± 8.31 cfm: 15 % higher compared to NaCl particles. We also observed that moving the C-R box farther away from the measurement devices (140 inches vs 65 inches) led to a decrease in CADR by ∼8 %. However, using additional mixing fans helped improve CADR in the room's corners by up to 21 %. Comparison of CADR determined by an out-of-the-box consumer-grade AirVisual monitor with MiniWRAS showed that the AirVisual yielded the same trends, albeit at a ∼14 % higher CADR. Our investigation of variables affecting the measured C-R box's CADR will help optimize its performance and improve data comparison across studies. We also demonstrate that consumer-grade monitors are a viable option in investigating the performance of air cleaners, especially their localized performance. • - • Higher filter MERV ratings and higher C-R box's fan speeds yield higher CADR. • Use of mixing fans increases CADR in stagnant air pockets, e.g., room corners. • Low-cost monitor AirVisual could be used to measure the performance of air cleaners. • A larger distance between the measurement device and the C-R Box lowers CADR. • Test particle type affects observed CADR of the C-R box.