2024 Yes Ultrafine and Fine Particulate Matter Inside andOutside of Mechanically Ventilated Buildings https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5334682/ Miller, Shelly North America Review Elementary (K-5) Ventilation rates Temperature Carbon Dioxide (CO2) Nitrogen Dioxide (NO2) Aerosols Ultrafine particles Particle number count Infiltration Nitrate Ultrafine and fine PM were measured in four mechanically ventilated buildings. Indoor PM tracked outdoor levels, with significant nighttime infiltration. Findings highlight the need for enhanced filtration, especially for ultrafine particles in schools. 2017