Performance Evaluation of Particulate Matter and Indoor Microclimate Monitors in University Classrooms under COVID-19 Restrictions

Abstract

Optical monitors have proven their versatility into the studies of air quality in the workplace and indoor environments. The current study aimed to perform a screening of the indoor environment regarding the presence of various fractions of particulate matter (PM) and the specific thermal microclimate in a classroom occupied with students in March 2019 (before COVID-19 pandemic) and in March 2021 (during pandemic) at Valahia University Campus, Targoviste, Romania. The objectives were to assess the potential exposure of students and academic personnel to PM and to observe the performances of various sensors and monitors (particle counter, PM monitors, and indoor microclimate sensors). PM1 ranged between 29 and 41 μg m^-3 and PM10 ranged between 30 and 42 μg m^-3. It was observed that the particles belonged mostly to fine and submicrometric fractions in acceptable thermal environments according to the PPD and PMV indices. The particle counter recorded preponderantly 0.3, 0.5, and 1.0 micron categories. The average acute dose rate was estimated as 6.58 × 10^-4 mg/kg-day (CV = 14.3%) for the 20-40 years range. Wearing masks may influence the indoor microclimate and PM levels but additional experiments should be performed at a finer scale.

Keywords: PM1; PM2.5; acute dose rate (ADR); mask wearing; particle counter; predicted mean vote (PMV); predicted percentage of dissatisfied (PPD); size segregated mass fractions; thermal microclimate.

Figure A1

Instrumentation used in the current study (particle counter, PM monitor, and thermal microclimate equipment).

Figure A2

Screen capture of DeltaLog 10 software showing the data acquisition performed during the practical works of Group D.

Figure A3

Screen capture of DeltaLog 10 software presenting the thermal sensation assessment based on PMV and PPD indices.

Figure A4

Screen capture of ExpoFIRST Version 2.0 application for inhalation dose calculation (EPA’s exposure factors interactive resource for scenarios tool https://cfpub.epa.gov/ncea/risk/recordisplay.cfm?deid=322489#tab-3, accessed on 5 June 2021).

Figure 1

Time series of the concentrations of the size segregated mass fractions of particulate matter (μg m⁻³) recorded in a classroom using a TSI DustTrak^TM DRX 8533 EP during three hours of lectures and the equations of corresponding linear trendlines: (a) Group A: y = −0.0618x + 43.436 (R² = 0.86); (b) Group B: y = −0.0288x + 33.429 (R² = 0.69) ; (c) Group C: y = −0.0002x + 30.3994 (R² = 0.00); (d) Group D: y = 0.0214x + 39.407 (R² = 0.06).

Figure 2

Example of the raw time series recorded by the DeltaOHM indoor microclimate system during the practical works of Group D (Tw—wet bulb temperature with natural ventilation; Tg—globe thermometer temperature; Ta—ambient temperature; Pr—vapor pressure).

Figure 3

Acute dose rates estimated for the groups of students (A, B, D—mixed groups; C—only females); columns order: 20–40 years; 20–30 years; 31–40 years.