Pilot Study on the Physical, Chemical, and Biological Determinants of Indoor Air Quality in University Classrooms
Authors: Edelmers Edgars , Kauce Rūta , Konopecka Vita , Veignere Elizabete , Sprūdža Klinta Luīze , Neļķe Valters , Citskovska Elizabete , Šipilova Viktorija , Čikuts Matīss , Skrebele Elizabete , Skadiņš Ingus , Martinsone Žanna , Borodinecs Anatolijs 
Published: November 2023

Abstract
In the context of an escalating energy crisis, the burgeoning prevalence of remote work, and challenging climatic conditions, ensuring optimal indoor air quality (IAQ) has emerged as a pressing concern. This pilot study rigorously investigates the complex interplay between biological, chemical, and physical parameters that characterize IAQ, focusing specifically on university classrooms during active teaching sessions. Employing a comprehensive array of instrumentation – such as SAS SUPER ISO 100 for microbiological sampling, Aranet4 for monitoring relative humidity, temperature, and CO2 concentration, and PCE-PCO 1 and PCE-RSCM 16 for particulate matter (PM2.5 and PM10) quantification—the study spanned a duration of three days in November 2022 and covered classrooms of varying dimensions, both reliant on natural ventilation. An extensive collection of 52 microbiological samples were obtained and cultured on specialized growth media to differentiate between various classes of airborne microorganisms. Concurrently, the pilot study meticulously recorded students’ activity patterns, along with the temporal dynamics of window openings and closures. The colony-forming units per cubic meter (CFU/m3) fluctuated between 174 and 934 CFU/m3, with fungi constituting the majority. Furthermore, the CFU/m3 for fungi cultivated on Sabouraud Dextrose Agar ranged from 24 to 610 CFU/m3, whereas bacteria cultured on Trypticase Soy Agar and Mannitol Salt Agar exhibited ranges of 42–476 CFU/m3 and 42–254 CFU/m3, respectively. Contrasting these findings with extant guidelines that recommend microbiological contamination not exceeding 500 CFU/m3 highlights significant IAQ concerns. Thermal assessments revealed that the smaller classroom surpassed the acceptable indoor temperature threshold of 25 °C within an average duration of 50 minutes, while the larger classroom remained compliant. Notably, the highest CO2 concentrations recorded over the three-day period were alarmingly high: 2689 ppm, 1970 ppm, and 2131 ppm on the first, second, and third days, respectively. A 25-minute ventilation intervention was sufficient to reduce CO2 levels to 499 ppm, although existing literature stipulates that CO2 concentrations should not surpass 1000 ppm. Importantly, the pilot study highlighted the rapid increasing of PM2.5 and PM10 concentrations in crowded instructional settings, averaging 400 μg/m3 and 35 μg/m3, respectively. This underscores the necessity for a continuous air ventilation and purification mechanism during classroom activities. Despite these pivotal findings, the study identifies a glaring absence of standardized regulations or guidelines pertaining to maximum acceptable concentrations of particulate matter and microbial CFU in public indoor environments, indicating a critical area requiring immediate policy intervention.