Airborne metals and particulate matter measured inside and outside farmworker homes with evaporative coolers and air filtration interventions

Evaporative ("swamp") coolers (ECs) are used for cooling of homes in hot and arid climates. Because ECs draw in large volumes of outdoor air, they can introduce substantial amounts of ambient airborne particulate matter (PM) and other pollutants indoors, which is especially exacerbated during wildfire smoke events. We measured airborne metals and PM inside and outside farmworkers' homes with ECs in the California San Joaquin Valley, U.S.A. Sampling was conducted as part of a larger study (FRESSCA, Filtration for Respiratory Exposure to wildfire Smoke from Swamp Cooler Air) to develop and evaluate an affordable EC filtration solution. All homes received portable air cleaners (PACs), and approximately half the homes received filters on their EC air intakes. Indoor and outdoor airborne metals were actively measured using 24-hr air sampling. Airborne metals were dominated by Fe, with some detections of Cu, Mn, Zn, and Se. Indoor/outdoor (I/O) ratios for Fe were mostly <1 and were lower for homes with EC filters. Metals analyses of the EC filters themselves revealed additional metals, likely due to the longer sampling time. These metals were partially removed from the air entering participants' homes by EC filters. Passive PM samplers were deployed for 70 days and analyzed using electron microscopy. PM samples revealed crustal, carbonaceous, and agriculture-related particle types, including Cu-rich fungicides. PM levels were lower indoors compared to outdoors in all homes (30%-70%). Some evidence of greater PM reductions in homes with EC filters was observed, with 25% reductions in coarse PM_10-2.5 in homes with EC filters that used their ECs more frequently (<i>p</i> < 0.05). Few smoke events during the study limited our ability to detect differences in PM from wildfires. However, the measured reductions in coarse PM are important for communities heavily impacted by dust, both for home cleanliness and for protection from upper-airway health impacts.<i>Implications</i>: Do-it-yourself evaporative cooler filters are a promising and affordable method of reducing dust infiltration in homes burdened by heat stress and poor outdoor air quality. Further evaluation during wildfire smoke events and optimization of evaporative cooler filter interventions could eventually reduce respiratory-related health impacts in communities affected by a changing climate.