Indoor air quality and student welfare: The Effect of Indoor Air Purifiers in Schools

Last registered on December 15, 2023


Trial Information

General Information

Indoor air quality and student welfare: The Effect of Indoor Air Purifiers in Schools
Initial registration date
August 21, 2023

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
August 24, 2023, 6:25 AM EDT

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

Last updated
December 15, 2023, 4:31 AM EST

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


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Primary Investigator

Politecnico di Milano

Other Primary Investigator(s)

PI Affiliation
RFF‐CMCC: European Institute on Economics and the Environment (EIEE), Centro Euro‐Mediterraneo sui Cambiamenti Climatici (CMCC)
PI Affiliation
RFF‐CMCC: European Institute on Economics and the Environment (EIEE), Centro Euro‐Mediterraneo sui Cambiamenti Climatici (CMCC)
PI Affiliation
Politecnico di Milano

Additional Trial Information

In development
Start date
End date
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
Bad air quality is a significant problem for children, as it can cause various clinical and subclinical problems, including respiratory infections, asthma, allergies, absenteeism, and cognitive impairment. In this registered report, we present the design of a \textit{cluster randomized control trial} on the potential benefits (and cost-effectiveness) of installing air purifiers in schools to reduce children's exposure to poor air quality conditions. We randomly assign 95 classes in three schools to receive or not air purifiers and estimate their effects on indoor air pollution, absenteeism, achievement, cognitive ability, and behavioral outcomes related to mood and aggression. We expect to find a relevant increase in school attendance, learning, cognitive outcomes, and the general well-being of children. The results of this study would allow policymakers to understand the benefits of a scalable defensive strategy to mitigate the exposure of vulnerable groups to a relevant environmental stressor.
External Link(s)

Registration Citation

Bonan, Jacopo et al. 2023. "Indoor air quality and student welfare: The Effect of Indoor Air Purifiers in Schools." AEA RCT Registry. December 15.
Experimental Details


Our intervention involves installing 43 consumer-grade air purifiers in randomly selected classes in three schools. The purifiers contain a ULPA-U15 filter that filters up to 99.99% of particles larger than 0.026 microns. The purifier passes polluted air through the ULPA filter, which is made of layers of ultrafine materials capable of blocking fine particles, and an activated carbon filter that purifies the air before it is returned to the environment.
Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
Students' absences
Indoor air pollution (PM2.5)
Cognitive ability
Standardized test scores
Mood and aggressive behavior
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Subjective health status
Students' intermediate and final grades
Other indoor pollutants (CO, VOC)
Behavioral response: n. of times windows are opened
Students' environmental concerns and awareness
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
We randomly assign about half of the classes to treatment or control, while stratifying them by school and grade. The intervention is not accompanied by specific information campaigns or communications to teachers or parents. All purifiers operate continuously throughout the study period between October 2023 and June 2024. In addition to the purifiers, we randomly install 38 indoor air quality monitors in a random subsample of classes. We stratify by school, treatment status, and class characteristics such as floor and orientation, that is, whether the class faces the street or the internal courtyard. The monitors measure the concentration of CO2, VOC, PM2.5, CO, temperature, humidity, and atmospheric pressure at sub-hour intervals.
Experimental Design Details
Not available
Randomization Method
Randomization is performed by researchers in the presence of each school's director using a random number generator.
Randomization Unit
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
95 classes
Sample size: planned number of observations
2090 students
Sample size (or number of clusters) by treatment arms
43 treated classes with air purifiers, 52 control classes without purifiers
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)

Institutional Review Boards (IRBs)

IRB Name
Politecnico di Milano
IRB Approval Date
IRB Approval Number
Analysis Plan

Analysis Plan Documents

Pre-analyis plan

MD5: 1348b750359b17a655ea0a11d8693294

SHA1: 5f65dce5fc942fa37be067ed1270f8e2dc1a270a

Uploaded At: August 21, 2023