Investigation and Health Risk Assessment of Indoor and Outdoor Nitrogen Dioxide at Preschools in Haze Areas of Lampang Province and Industrial Areas of Rayong Province, Thailand

Nitrogen dioxide (NO2) is a major indoor air pollutant and a significant ambient air contaminant associated with health effects, especially for students and teachers who attend schools in the areas of traffic, roads and industry. This study aims to assess the impacts of NO2 exposure on the health of students in haze and industrial areas from November 2023 to March 2024. Researchers utilized tube-type passive samplers to collect indoor and outdoor NO2 samples, which were subsequently analyzed via spectrophotometry. The results revealed that the weekly mean indoor and outdoor NO2 concentrations in the haze areas (HA1–HA5) ranged between 4.4–29.0 and 4.0–37.9 µg m-3, respectively. The ranges of indoor and outdoor NO2 in industrial areas (ID1–ID5) were 4.9–34.7 and 5.0–37.9 µg m-3, respectively. The indoor levels of NO2 were lower than the World Health Organization (WHO) standard of 40 µg m-3, whereas the outdoor levels were above the WHO recommended limit of 10 µg m-3, approximately 84–89%. The highest levels of NO2 in haze and industrial areas were influenced by the haze episode in Thailand. NO2 and PM2.5 levels in haze (r = 0.441–0.475) and industrial areas (r = 0.667–0.734) were significantly correlated. The noncarcinogenic risk for chronic exposure to NO2, both indoors and outdoors (HQ>1.0), indicates that exposure significantly affects children and that long-term exposure could result in the accumulation of effects in adults, especially in industrial areas.