Assessment of CO2 and aerosol (PM2.5, PM10, UFP) concentrations during the reopening of schools in the COVID-19 pandemic: The case of a metropolitan area in Central-Southern Spain

Abstract

Public health authorities have been paramount in guaranteeing that adequate fresh air ventilation is promoted in classrooms to avoid SARS-CoV-2 transmission in educational environments. In this work it was aimed to assess ventilation conditions (carbon dioxide, CO 2 ) and suspended particulate matter (PM 2.5 , PM 10 and UFP) levels in 19 classrooms – including preschool, primary and secondary education – located in the metropolitan area of Ciudad Real, Central-Southern Spain, during the school’ reopening (from September 30th until October 27th, 2020) after about 7 months of lockdown due to COVID-19 pandemic. The classrooms that presented the worst indoor environmental conditions, according to the highest peak of concentration obtained, were particularly explored to identify the possible influencing factors and respective opportunities for improvement. Briefly, findings suggested that although ventilation promoted through opening windows and doors according to official recommendations is guaranteeing adequate ventilation conditions in most of the studied classrooms, thus minimizing the risk of SARS-CoV-2 airborne transmission, a total of 5 (26%) surveyed classrooms were found to exceed the recommended CO 2 concentration limit value (700 ppm). In general, preschool rooms were the educational environments that registered better ventilation conditions, while secondary classrooms exhibited the highest peak and average CO 2 concentrations. In turn, for PM 2.5 , PM 10 and UFP, the concentrations assessed in preschools were, on average about 2-fold greater than the levels obtained in both primary and secondary classrooms. In fact, the indoor PM 2.5 and PM 10 concentrations substantially exceeded the recommended limits of 8hr-exposure, established by WHO, in 63% and 32% of the surveyed classrooms, respectively. Overall, it is expected that the findings presented in this study will assist the establishment of evidence-based measures (mainly based on ensuring proper ventilation rates and air filtration) to mitigate preventable environmental harm in public school buildings, mainly at local and national levels.

CO2 concentration monitoring inside educational buildings as a strategic tool to reduce the risk of Sars-CoV-2 airborne transmission

“…Similarly, the CO 2 mean levels observed in this study revealed to be lower than those documented for the European educational buildings in the cross-sectional European Union-funded HESE (Health Effects of School Environment) study and, more specifically, up to half of the mean values determined in 16 classrooms of 8 schools in Italy (Simoni et al, 2006, 2010 ); even if similar maximum values were found. On the other hand, according to Villanueva et al (2021) , the pre-school (classroom 2) was the educational environment showing the lowest mean and maximum values of CO 2 concentration probably due to the presence of seven transom windows always open (as reported in the questionnaires).…”

“…It's important to underline that during the first day, inside the classroom 6, 20 students and 1 teacher were present while inside the classroom 5, the total number of bystanders was 12 (11 students and 1 teacher). Anyway, other classrooms characterized by a high number of persons, for instance the classroom 4 (21) and 9 (19), showed CO 2 levels lower than those monitored in classroom 6 probably due to a more efficient ventilation strategy in terms of frequency and duration of windows and door opening as well as to hourly cross-ventilation ( Villanueva et al, 2021 ) ( Fig. 2 and Table 2 ).…”

“…This evidence can be explained by the absence of windows in the hallway facing the classroom that limited the effectiveness of the cross-ventilation. This is the case when structural limits of the educational building play a crucial role negatively affecting the indoor air quality and potentially promoting the airborne viral transmission ( Villanueva et al, 2021 ).

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“…The provided recommendations are in line with the ventilation strategies inside indoor environments promoted by building environments-related international organizations such as REHVA ( Federation of European Heating, Ventilation and Air Conditioning Associations ) and ASHRAE (American Society of Heating, Ventilating and Air Conditioning Engineers) to primarily improve air quality ( ASHRAE, 2020 ; REHVA, 2020). The achievement of adequate ventilation indoors through the implementation of similar recommendations has been also recognized in the recent scientific literature as the necessary condition to reduce airborne viral transmission (Morawska, 2021; Villanueva, 2021 ).…”

Dynamic Evaluation of the Effects of Climate Change on the Energy Renovation of a School in a Mediterranean Climate

“…A large part of energy consumption in Italy is caused by poor maintenance and renovation of school buildings [22]. In addition, the current pandemic of SARS-CoV-2 has highlighted numerous deficits in buildings and the need has emerged to adequately ventilate indoor spaces [23,24], especially schools that, unlike other non-residential buildings, had to remain open even at crucial times of the spread of the virus, despite their worst indoor environmental conditions [25]. Here, to the problem of overheating and, therefore, the need to increase the capacity of the cooling system, is added the need to further increase the loads through the installation of forced ventilation systems, worsening electricity demands.…”