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Widespread North American wildfires in 2023 led to exposure to ambient wildfire smoke outside of traditionally wildfire-prone regions. The objective was to evaluate levels of indoor air pollutants in relation to ambient wildfire smoke exposure in eastern Massachusetts. Using a real-time multipollutant sensor system in five Boston area households, this study assessed indoor fine particulate matter (PM 2.5 ), nitrogen dioxide (NO 2 ), and total volatile organic compound concentrations (TVOC) two days before and during days of hazardous wildfire smoke exposure (smoke days). The relationship between ambient PM 2.5 from regulatory monitors and indoor PM 2.5 before and during smoke days was investigated by mixed effects linear regression. During smoke days and the preceding non-smoke days, median indoor PM 2.5 was 9.9 µg/m 3 and 3.5 µg/m 3 ( p  < 0.001), respectively; median NO 2 was 20.5 ppb and 18.4 ppb ( p  = 0.11); median TVOC was 6,715 µg/m 3 and 5,361 µg/m 3 ( p  = 0.35). A 1% increase in ambient PM 2.5 was associated with a 0.93% increase in indoor PM 2.5 on smoke days (95% CI, 0.54%-1.32%) and a 0.34% increase on non-smoke days (95% CI, 0.17%-0.66%), though interaction testing of smoke day status was not statistically significant ( p  = 0.14). In Northeastern US homes, indoor PM 2.5 increased significantly during ambient wildfire smoke exposure, which may reflect increased infiltration and increased indoor particle-generating activities during smoke days. Implications : This study reports on household exposure to wildfire smoke in eastern Massachusetts, finding that indoor PM 2.5 more than doubled compared to preceding non-smoke days, while indoor NO 2 and TVOC did not significantly rise. Though the generalizability of this study is limited by the small number of homes studied, the findings suggest that more investigation is needed to understand indoor air pollution during future wildfire smoke exposure in regions not traditionally wildfire-prone and to inform mitigation efforts.

Background: Endotoxins are stimulators of the immune system and, despite their potential to protect against allergy, have been associated with early wheezing and asthma morbidity., Objective: To compare inner-city school endotoxin exposure with home endotoxin exposure in children with asthma., Methods: Students with asthma were recruited from 12 urban elementary schools. Settled and airborne dust samples, linked to enrolled students, were collected from school classrooms, gymnasiums, and cafeterias twice during the academic year. For comparison, settled dust was collected once from the bedrooms of students with asthma., Results: Two hundred twenty-nine school settled dust samples and 118 bedroom settled dust samples were collected and analyzed for endotoxin. The median endotoxin concentration for school samples was 13.4 EU/mg (range, 0.7-360.7 EU/mg) and for home samples was 7.0 EU/mg (range = LLOD-843.0 EU/mg). The median concentration within each individual school varied from 6.6 EU/mg to 24.0 EU/mg. One hundred four students with asthma had matched classroom and bedroom endotoxin exposure measurements performed in the same season and demonstrated significantly higher concentrations of endotoxin in the students' classrooms (mean log value, 1.13 vs 0.99, P = .04). The median of the classrooms was 12.5 EU/mg compared with their bedrooms, with a median of 7.0 EU/mg. Within the school environment, no significant difference was seen between the fall and spring samples (mean log value 1.14 vs 1.09; P = .35)., Conclusion: Inner-city children with asthma were exposed to higher concentrations of endotoxin in their classrooms as compared with their bedrooms. Further studies are needed to evaluate school endotoxin exposure as a factor in asthma morbidity., (Copyright © 2012 American College of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.)