Associations between indoor air exposures and cognitive test scores among university students in classrooms with increased ventilation rates for COVID-19 risk management.

Background: Past work demonstrating an association between indoor air quality and cognitive performance brought attention to the benefits of increasing outdoor air ventilation rates beyond code minimums. These code minimums were scrutinized during the COVID-19 pandemic for insufficient ventilation and filtration specifications. As higher outdoor air ventilation was recommended in response, questions arose about potential benefits of enhanced ventilation beyond infection risk reduction.

Objective: This was investigated by examining associations between indoor carbon dioxide concentrations, reflective of ventilation and building occupancy, and cognitive test scores among graduate students attending lectures in university classrooms with infection risk management strategies, namely increased ventilation.

Methods: Post-class cognitive performance tests (Stroop, assessing inhibitory control and selective attention; Arithmetic, assessing cognitive speed and working memory) were administered through a smartphone application to participating students (54 included in analysis) over the 2022-2023 academic year in classrooms equipped with continuous indoor environmental quality monitors that provided real-time measurements of classroom carbon dioxide concentrations. Temporally and spatially paired exposure and outcome data was used to construct mixed effects statistical models that examined different carbon dioxide exposure metrics and cognitive test scores.

Results: Model estimates show directionally consistent evidence that higher central and peak classroom carbon dioxide concentrations, indicative of ventilation and occupancy, are associated with lower cognitive test scores over the measured range included in analysis ( ~ 440-1630 ppm). The effect estimates are strongest for 95th percentile class carbon dioxide concentrations, representing peak class carbon dioxide exposures.

Impact statement: As the COVID-19 pandemic eased, questions emerged on the benefits of increased outdoor air ventilation beyond infection reduction. This work assesses associations between carbon dioxide concentrations, indicative of ventilation and occupancy, and cognitive test scores among students in university classrooms with increased outdoor air ventilation. Although not causal, models show statistically significant evidence of associations between lower carbon dioxide concentrations and higher cognitive test scores over the low range of carbon dioxide exposures in these classrooms. While the underlying mechanisms remain unknown, higher outdoor air ventilation appears to provide additional benefits by reducing indoor air exposure and supporting student performance.