Impact of Air Conditioning Type on Outdoor Ozone Intrusion into Homes in a Semi-Arid Climate.

Outdoor ozone (O₃) is elevated on hot, sunny days when residential air conditioning is used most. We evaluated the impact of direct evaporative coolers (ECs) and vapor-compression air conditioners (ACs) on indoor O₃ concentrations in homes (N = 31) in Utah County, Utah, United States of America. Indoor and outdoor O₃ concentrations were measured for 24 h at each home using nitrite-impregnated glass-fiber filters. AC homes (n = 16) provided a protective envelope from outdoor O₃ pollution. Only one AC home had O₃ levels above the limit of detection (LOD). Conversely, EC homes (n = 15) provided minimal protection from outdoor O₃. Only one EC home had O₃ levels below the LOD. The average indoor O₃ concentration in EC homes was 23 ppb (95% CI 20, 25). The indoor-to-outdoor (I/O) ratio for O₃ in EC homes was 0.65 (95% CI 0.58, 0.72), while the upper bound for the I/O ratio for AC homes was 0.13 (p < 0.001). Indoor exposure to O₃ for residents in EC homes is approximately five times greater than for residents of AC homes. Although ECs offer energy and cost-saving advantages, public health awareness campaigns in O₃-prone areas are needed, as well as research into O₃ pollution controls for direct ECs such as activated carbon filtration. [ABSTRACT FROM AUTHOR]