Comparison of Indoor Air Quality Concentrations in Childcare Centers across Metropolitan Cities and Provinces

We measured and compared indoor air quality (PM_2.5, PM₁₀, CO₂, CO, HCHO, and TCM) in 1,338 childcare centers, including 386 in Gyeongsangnam-do, 238 in Gyeongsangbuk-do, 499 in Busan, 101 in Ulsan, and 114 in Daegu. The measurements were conducted over a period of four years, from 2020 to 2023, primarily between July and December. The ratio of fine particulate matter (PM_2.5) to particulate matter (PM₁₀) was generally between 0.3 and 0.4, which is lower compared to the external air ratio of 0.4 to 0.6. Both PM_2.5 and PM₁₀ concentrations were below the levels of the indoor air quality maintenance standards of 35 μg/m³ and 75 μg/m³, respectively. Carbon dioxide (CO₂) levels ranged from 51.25% to 62.50%, which was higher than the external air CO₂ concentration of 400 ppm, but none of the childcare centers exceeded the standard concentration of 1,000 ppm. Carbon monoxide (CO) levels were also significantly higher than the external air level of 0.4 ppm, with some locations recording 10 times higher than the external air level. Formaldehyde (HCHO) levels showed similar trends across regions and years, with Gyeongsangbuk-do having the highest concentration at 18.5 μg/m³, but still far below the indoor air quality management standard of 80 μg/m³. Total airborne bacteria levels were highest in Daegu, with the average value of 60.3 CFU/m³ over the four years, while other regions ranged from 50.4 CFU/m³ to 58.1 CFU/m³, showing similar trends.