Characterizing particle number size distributions and source contribution for public elementary school classrooms in bangkok

This study characterizes particle number size distributions (PNSD) and source contributions for public elementary school classrooms in Bangkok. Using Scanning Mobility Particle Sizers (SMPS) and Optical Particle Sizers (OPS), measurements covered particle sizes from 10 nm to 10 µm during regular school hours on weekdays and under various experimental conditions on weekends. The particle number concentrations (PNC) showed significant fluctuations for all four schools with peak levels observed during morning rush hours coinciding with students' arrival and indoor activities. The findings revealed predominant Aitken mode particles both indoors and outdoors. During weekdays, the PNSD was significantly unimodal, with sigma (σ) values for indoor environments ranging from 1.2 to 2.4, geometric mean diameters (Dpgi) from 23 to 115 nm, and total particle number concentrations (N) between 2300 and 32000 particles/cm³. For outdoor environments, σ ranged from 1.7 to 2.6, with diameters between 25 to 110 nm, and N ranging from 3000 to 27000 particles/cm³. On weekends, PNSD at the four school sites displayed significant a single mode. Indoor measurements showed (Dpgi) ranging from 17 to 125 nm, (N) varying between 2000 and 87500 particles/cm³, and sigma (σ) values spanning from 1.3 to 2.5, with the highest concentrations observed during cleaning times and sudden changes from window open to closed conditions. The weekday indoor/outdoor (I/O) ratio at four school sites varied significantly, ranging from 0.7 to 3.9, reflecting the impact of indoor activities and outdoor air quality. The highest I/O ratio of 3.9 was observed at Site S2 during which lunch was eaten in the classroom. This highlights the influence of lunch and cleaning activities and some effect of infiltrated outdoor air influenced high-traffic areas on indoor air quality. The weekend I/O ratios varied from 0.4 to 6.8, with the highest observed during closed-window conditions (C5), highlighting the significant impact of ventilation and cleaning activities on indoor air quality. For weekdays, the indoor source rates for ultrafine particles (10 -100 nm) ranged from 2.1 × 1010 to 34.2 × 1010 #/s, for fine particles (100-1000 nm) from 0.2 × 1010 to 50 × 1010 #/s, and for larger particles (1000-10000 nm) from 1.9 × 106 to 11.2 × 1010 #/s. For weekends, the indoor source rates for ultrafine particles (10-100 nm) ranged from 0.3 × 1010 to 58.0 × 1010 #/s, for fine particles (100-1000nm) from 0.3 × 10^10 to 19.7 × 1010 #/s, and for larger particles (1000-10000 nm) from 0.7 × 107 to 53.9 × 107 #/s. These findings highlight the critical influence of nearby traffic, classroom activities, and cleaning activities on indoor air quality, emphasizing the need for improved ventilation strategies and controlled indoor practices. Recommendations include enhancing filtration systems, improving ventilation strategies, and implementing regular maintenance protocols to reduce the impact of both outdoor and indoor pollution sources, ensuring a healthier learning environment. The study underscores the importance of targeted interventions to create healthier educational environments for children, aligning with WHO guidelines and supporting sustainable development goals for good health, quality education, and sustainable cities.