Pollution and Cognitive Performance: A Field Experiment in High Schools

Last registered on November 11, 2025
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Pre-Trial

Trial Information

General Information

Title
Pollution and Cognitive Performance: A Field Experiment in High Schools
RCT ID
AEARCTR-0016324
Initial registration date
July 03, 2025

Initial registration date is when the trial was registered.

It corresponds to when the registration was submitted to the Registry to be reviewed for publication.

First published
July 03, 2025, 3:56 PM EDT

First published corresponds to when the trial was first made public on the Registry after being reviewed.

Last updated
November 11, 2025, 10:55 AM EST

Last updated is the most recent time when changes to the trial's registration were published.

Locations

Country
Netherlands
Region
Limburg

Primary Investigator

Name
Juan Palacios
Affiliation
Maastricht University
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Other Primary Investigator(s)

PI Name
Nils Kok
PI Affiliation
Maastricht University
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PI Name
Mariët Bogaard
PI Affiliation
Maastricht University
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Additional Trial Information

Status
In development
Start date
2025-06-08
End date
2028-01-01
Keywords
Education, Environment & Energy
Additional Keywords
PM2.5, high schools, pollution, learning, educational performance, air filters, purifiers, field experiment
JEL code(s)
Q53, I21, C93
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
Abstract
Poor indoor air quality has been increasingly linked to adverse health outcomes and diminished cognitive performance, yet evidence on effective and scalable interventions remains limited. This study investigates the causal impact of indoor air pollution removal on academic performance among high school students in a region historically exposed to elevated pollution levels. Leveraging a randomized controlled trial across secondary schools, we deploy high-efficiency air filtration devices and real-time air quality sensors during standardized exam weeks. Treatment classrooms receive active air filtration prior to and during testing, while control classrooms remain untreated, with some assigned to a placebo condition involving inactive devices. Treatment is randomly assigned within parallel class pairs (same school, year, track), ensuring internal validity and minimizing contamination. Environmental data collected from both treatment and control classrooms will be used to quantify differences in particulate matter concentrations (PM₂.₅ and PM₁₀), while student test scores will serve as the primary outcome of interest. By combining high-frequency environmental monitoring with administrative academic performance data, this project provides policy-relevant evidence on the role of indoor environmental interventions in improving educational outcomes and human capital formation.
External Link(s)

Registration Citation

Citation
Bogaard, Mariët, Nils Kok and Juan Palacios. 2025. "Pollution and Cognitive Performance: A Field Experiment in High Schools." AEA RCT Registry. November 11. https://doi.org/10.1257/rct.16324-2.0
Sponsors & Partners

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Experimental Details

Interventions

Intervention(s)
The core intervention in this study consists of the deployment of high-efficiency particulate air (HEPA) filtration units in middle school classrooms. The primary objective is to remove fine particulate matter (PM) from the indoor environment in a controlled and replicable manner, thereby isolating the causal effect of improved air quality on student academic performance.
Intervention Start Date
2025-09-01
Intervention End Date
2026-06-30

Primary Outcomes

Primary Outcomes (end points)
The primary outcomes of interest in this study are student academic performance in standardized exams and indoor air pollution levels PM2.5.
Primary Outcomes (explanation)
Primary Outcomes (Explanation)
The primary outcomes of interest in this study are student academic performance in standardized exams and indoor air pollution levels PM2.5. These outcomes align with the main research objective: estimating the causal effect of improved indoor air quality—achieved via HEPA filtration—on cognitive performance in middle school students.

1. Academic Performance

The main educational outcome is exam score at the student-test level. Each student is expected to take three written tests (Dutch, English, and Mathematics) during two different testing periods (e.g., winter and spring). The raw outcome is the numerical grade assigned to each test by the teacher, obtained from the central digital platform SomToday. The primary academic outcome variable will be Standardized exam score (z-score) by subject and test period.

PM readings are taken every minute by air quality sensors and aggregated into 5-minute averages. The primary environmental outcome variable will be measures of PM concentration in classroom during exam hours (e.g., average, mean, average during mid exam time, late exam time).


Secondary Outcomes

Secondary Outcomes (end points)
The secondary outcomes in this study are designed to assess whether the air filtration intervention had unintended consequences on other indoor environmental conditions that may affect student well-being, test-taking experience, or the validity of the academic performance measure. These outcomes include:

Indoor noise levels (dB)
Carbon dioxide concentrations (CO₂, ppm)
Temperature (°C)
Relative humidity (%)
PM\textsubscript{10} concentrations (μg/m³)
TVOCs (Total Volatile Organic Compounds, ppb)
Secondary Outcomes (explanation)
Each of these secondary outcomes will be analyzed using the same empirical strategy as for the primary environmental outcomes, including:

Aggregated means by classroom and exam hour,
OLS regression models with classroom and time fixed effects.

Experimental Design

Experimental Design
The full-scale study employs a randomized controlled trial (RCT) design to estimate the causal impact of improved indoor air quality on student academic performance. The intervention consists of the deployment of 20 HEPA air filtration machines across a sample of 40 classrooms in five Dutch secondary schools during two scheduled exam periods in the 2025/2026 academic year. Randomization is conducted at the classroom–grade–track level, ensuring that for every treated classroom, there exists a parallel control classroom within the same school whose students follow the same curriculum and take the same exams during the testing period. This design allows for precise within-school comparisons and strengthens the internal validity of the estimated treatment effects.

Experimental Design Details
Not available
Randomization Method
Randomization done by a computer
Randomization Unit
Classroom
Was the treatment clustered?
Yes

Experiment Characteristics

Sample size: planned number of clusters
There will be 40 classrooms in the final experiment.
Sample size: planned number of observations
The study targets approximately 5,000 students, each completing three standardized tests in two separate exam rounds, yielding a total of 30,000 student-test observations.
Sample size (or number of clusters) by treatment arms
There will be 20 classrooms in the treatment and 20 classrooms in the control.
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
TBD
Supporting Documents and Materials

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IRB

Institutional Review Boards (IRBs)

IRB Name
Ethical Review Committee Inner City faculties (ERCIC) Maastricht
IRB Approval Date
2025-06-06
IRB Approval Number
ERCIC_707_22_04_2025_Kok
Analysis Plan

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