Development and laboratory evaluation of a do-it-yourself (DIY) filtration solution for residential evaporative coolers to reduce indoor wildfire smoke exposure

• Residential evaporative coolers (ECs) can introduce outdoor wildfire pollutants indoors. • We develop and lab-test a do-it-yourself (DIY) filtration solution for residential ECs. • DIY solution involves direct attachment of filters to EC intakes. • Deep-bed impregnated carbon MERV 13 met particle removal and airflow goals. • Future work will evaluate the DIY solution in real field settings. This work describes the development and laboratory evaluation of a do-it-yourself (DIY) filtration solution for residential evaporative coolers (ECs), which bring in large amounts of outside air during their operation, to reduce the infiltration of ambient pollutants during wildfire smoke events. We sought to identify an air filtration solution that could fit most residential ECs in the field; be relatively low-cost (under $100 USD); meet prevailing recommendations for wildfire smoke particle removal while not excessively restricting airflow; potentially remove gas-phase compounds in wildfire smoke; and be deployed for typical wildfire durations of a few days to weeks. We characterized the baseline performance of three common residential ECs in a laboratory setting and tested over 15 filters and media with different combinations and attachments. Our testing identified a simple DIY solution that involves direct attachment of filters to the exterior intakes of ECs using bungee straps. Our recommended DIY filtration solution that met performance goals uses 10-cm thick carbon-impregnated filters with a minimum efficiency reporting value (MERV) of 13, but cost goals are exceeded. Our recommended DIY solution that met goals for costs, particle removal, and airflow resistance, but not for volatile organic compound (VOC) removal, uses 10-cm thick MERV 13 filters without carbon-impregnation. Other alternative solutions include locally available lower-efficiency media or flat sheet media, albeit each with some drawbacks. Future work will evaluate the DIY solution in field settings to better understand in-situ performance and impacts on indoor particulate matter concentrations.