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Little information is available about air quality in early childhood education (ECE) facilities. We collected single-day air samples in 2010-2011 from 40 ECE facilities serving children ≤6 years old in California and applied new methods to evaluate cancer risk in young children. Formaldehyde and acetaldehyde were detected in 100% of samples. The median (max) indoor formaldehyde and acetaldehyde levels (μg/m ) were 17.8 (48.8) and 7.5 (23.3), respectively, and were comparable to other California schools and homes. Formaldehyde and acetaldehyde concentrations were inversely associated with air exchange rates (Pearson r = -0.54 and -0.63, respectively; P < 0.001). The buildings and furnishings were generally >5 years old, suggesting other indoor sources. Formaldehyde levels exceeded California 8-h and chronic Reference Exposure Levels (both 9 μg/m ) for non-cancer effects in 87.5% of facilities. Acetaldehyde levels exceeded the U.S. EPA Reference Concentration in 30% of facilities. If reflective of long-term averages, estimated exposures would exceed age-adjusted 'safe harbor levels' based on California's Proposition 65 guidelines (10 lifetime cancer risk). Additional research is needed to identify sources of formaldehyde and acetaldehyde and strategies to reduce indoor air levels. The impact of recent California and proposed U.S. EPA regulations to reduce formaldehyde levels in future construction should be assessed.

Although many U.S. children spend time in child care, little information exists on exposures to airborne particulate matter (PM) in this environment, even though PM may be associated with asthma and other respiratory illness, which is a key concern for young children. To address this data gap, we measured ultrafine particles (UFP), PM 2.5 , PM 10 , and black carbon in 40 California child-care facilities and examined associations with potential determinants. We also tested a low-cost optical particle measuring device (Dylos monitor). Median (interquartile range) concentrations for indoor UFP, gravimetric PM 2.5 , real-time PM 2.5 , gravimetric PM 10 , and black carbon over the course of a child-care day were 14 000 (11 000-29 000) particles/cm Dylos may be a valid low-cost alternative to monitor PM levels indoors in future studies. Overall, results indicate the need for additional studies examining particle levels, potential health risks, and mitigation strategies in child-care facilities. K E Y W O R D Sdaycare, early childhood education, indoor air, predictors matter (PM) in child-care facilities, despite children being more susceptible than adults to the health effects of PM exposures. | INTRODUCTION 9-11Particulate matter is a complex mixture of small particles and liquid droplets. Constituents include inorganic compounds (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles.Exposures of young children to PM 2.5 (particles with an aerodynamic diameter ≤2.5 μm) and PM 10 (aerodynamic diameter ≤10 μm) have been shown to increase allergen sensitization, decrease lung function, and exacerbate pre-existing respiratory conditions like asthma. 12-15Ultrafine particle (UFP, aerodynamic diameter <0.1 μm) exposure to young children has been associated with decreased lung function 16 and increased risk of respiratory hospital admissions. [12][13][14][15]17,18 In children, black carbon exposure has been associated with lung oxidative stress, 19-21 decreased lung function, 22 and respiratory symptoms. 23-25

One‐hundred seventy‐two households were recruited from regions with high outdoor air pollution (Fresno and Riverside, CA) to participate in a randomized, sham‐controlled, cross‐over study to determine the effectiveness of high‐efficiency air filtration to reduce indoor particle exposures. In 129 households, stand‐alone HEPA air cleaners were placed in a bedroom and in the main living area. In 43 households, high‐efficiency MERV 16 filters were installed in central forced‐air heating and cooling systems and the participating households were asked to run the system on a clean‐air cycle for 15 min per hour. Participating households that completed the study received true air filtration for a year and sham air filtration for a year. Air pollution samples were collected at approximately 6‐month intervals, with two measurements in each of the sham and true filtration periods. One week indoor and outdoor time‐integrated samples were collected for measurement of PM2.5, PM10, and ultrafine particulate matter (UFP) measured as PM0.2. Reflectance measurements were also made on the PM2.5 filters to estimate black carbon. True filtration significantly improved indoor air quality, with a 48% reduction in the geometric mean indoor PM0.2 and PM2.5 concentrations, and a 31% reduction in PM10. Geometric mean concentrations of indoor/outdoor reflectance values, indicating fraction of particles of outdoor origin remaining indoors, decreased by 77%. Improvements in particle concentrations were greater with continuously operating stand‐alone air cleaners than with intermittent central system filtration. Keeping windows closed and increased utilization of the filtration systems further improved indoor air quality.

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