Indoor air quality in primary school classrooms in Sweden, Slovakia, and the United Arab Emirates

The indoor environment was investigated in 75 primary school classrooms in three countries with different climate zones, building types and cultural and social aspects. Temperature, relative humidity and concentrations of CO₂, formaldehyde, TVOC, NO₂, ozone and particulate matter (PM) were measured over a one-week period in 45 schools in Sweden (winter), 15 schools in the United Arab Emirates (UAE; mild winter & hot summer) and in 15 schools in Slovakia (winter). The schools in the UAE were newer (average age 13 years vs. 70 in Sweden, 93 in Slovakia) and smaller (average volume 149 m³ vs. 174 m³ and 213 m³, respectively) with similar or higher occupancy. Schools in Sweden, mostly ventilated with mechanical ventilation operating with outdoor air, demonstrated the highest ventilation rates (median 3.2 h⁻¹ vs. 0.47 h⁻¹ in Slovakia and 0.57 h⁻¹ in UAE in winter) and lowest concentrations of most pollutants. Natural ventilation in Slovakia and mechanical ventilation with air recirculation in the UAE resulted in elevated concentrations of some of the pollutants. Median levels of CO₂ (1550 ppm in Slovakia, 1550 in UAE in winter), TVOC (434, 485 μg/m³, respectively) and NO₂ (12.2, 34.2 μg/m³, respectively) exceeded recommended guideline values. Lower median air change rates, ozone and NO₂ concentrations and higher CO₂, formaldehyde and TVOC concentrations were measured in the UAE in the summer than in the winter. Indoor environmental control strategies should take into account local environmental and building conditions and cultural factors in order to promote children's health, comfort, and learning.