Trial Outcomes & Findings for Effect of Air Pollution on the Cognitive Function of Adolescents (NCT NCT03762239)

Results Overview

This is a measure related to attentiveness that is calculated as hit reaction time standard error for correct responses (HRT-SE). A higher HRT-SE indicates highly variable reactions during the ANT test that is related to inattentiveness. A lower HRT-SE indicates indicates consistent reaction times and thus, a better attention performance.

Recruitment status

COMPLETED

Study phase

NA

Target enrollment

2123 participants

Primary outcome timeframe

Obtained from a test administered approximately 90 minutes after entering the classroom

Results posted on

2025-06-12

Participant Flow

To recruit participants (students), the objectives and design of the study were presented during teacher training sessions opened to all science teachers from all high schools of Barcelona metropolitan area. Teachers interested in participating signed up in an online form. Teachers from 33 high schools reached out to the research team to participate.

Based on 33 participating high schools, 2670 students were estimated eligible. As the total number of eligible students was not retrieved at the onset of the study, this estimation was based on the maximum number of students per class (n = 30), and thus it was likely to be overestimated. Of these, 547 individuals were excluded prior to randomization (parents or legal guardians who did not sign the consent form or students who declined to participate).

Participant milestones

Participant milestones
Measure	Purified Air Purifying the air with a Pure Airbox device (Zonair 3D). Use of air purifier (Pure Airbox, Zonair 3D) in the classroom 30 minutes before the participants enter the room and during the 2 hours of the experiment. Purifying the air with a Pure Airbox device (Zonair 3D): Purifying the air of the classroom where the experiment is conducted using a Pure Airbox device (Zonair 3D)	Normal Air Using a sham air purifier (same device without filters). Use of the same air purifier but without filters, so that it only recirculates the air without purifying it. Used for the same time period than the other arm. Using a sham air purifier (same device without filters): Use the air purifier (Pure Airbox, Zonair 3D) without filters in the classroom where the experiment is conducted
Overall Study STARTED	1068	1055
Overall Study COMPLETED	1067	1054
Overall Study NOT COMPLETED	1	1

Reasons for withdrawal

Reasons for withdrawal
Measure	Purified Air Purifying the air with a Pure Airbox device (Zonair 3D). Use of air purifier (Pure Airbox, Zonair 3D) in the classroom 30 minutes before the participants enter the room and during the 2 hours of the experiment. Purifying the air with a Pure Airbox device (Zonair 3D): Purifying the air of the classroom where the experiment is conducted using a Pure Airbox device (Zonair 3D)	Normal Air Using a sham air purifier (same device without filters). Use of the same air purifier but without filters, so that it only recirculates the air without purifying it. Used for the same time period than the other arm. Using a sham air purifier (same device without filters): Use the air purifier (Pure Airbox, Zonair 3D) without filters in the classroom where the experiment is conducted
Overall Study Appointment to the doctor	1	1

Baseline Characteristics

Race and Ethnicity were not collected from any participant.

Baseline characteristics by cohort

Baseline characteristics by cohort
Measure	Purified Air n=999 Participants Purifying the air with a Pure Airbox device (Zonair 3D). Use of air purifier (Pure Airbox, Zonair 3D) in the classroom 30 minutes before the participants enter the room and during the 2 hours of the experiment. Purifying the air with a Pure Airbox device (Zonair 3D): Purifying the air of the classroom where the experiment is conducted using a Pure Airbox device (Zonair 3D)	Normal Air n=994 Participants Using a sham air purifier (same device without filters). Use of the same air purifier but without filters, so that it only recirculates the air without purifying it. Used for the same time period than the other arm. Using a sham air purifier (same device without filters): Use the air purifier (Pure Airbox, Zonair 3D) without filters in the classroom where the experiment is conducted	Total n=1993 Participants Total of all reporting groups
Age, Continuous	14.7 years n=999 Participants	14.7 years n=994 Participants	14.7 years n=1993 Participants
Sex/Gender, Customized Sex · Female	514 Participants n=999 Participants	483 Participants n=994 Participants	997 Participants n=1993 Participants
Sex/Gender, Customized Sex · Male	481 Participants n=999 Participants	507 Participants n=994 Participants	988 Participants n=1993 Participants
Sex/Gender, Customized Sex · Other	4 Participants n=999 Participants	4 Participants n=994 Participants	8 Participants n=1993 Participants
Race and Ethnicity Not Collected	—	—	0 Participants Race and Ethnicity were not collected from any participant.
PMA-R, Primary Mental Aptitudes - Reasoning	17 score n=999 Participants	16 score n=994 Participants	16 score n=1993 Participants
HRT-SE, hit reaction time standard error	164.1 ms n=999 Participants	158.6 ms n=994 Participants	161.7 ms n=1993 Participants
Impulsivity	2 total score n=999 Participants	2 total score n=994 Participants	2 total score n=1993 Participants
Selective attention	0 total score n=999 Participants	0 total score n=994 Participants	0 total score n=1993 Participants
Alerting	34.5 ms n=999 Participants	35.5 ms n=994 Participants	34.5 ms n=1993 Participants
Orienting	14 ms n=999 Participants	14.8 ms n=994 Participants	14 ms n=1993 Participants
Conflict	78 ms n=999 Participants	76.5 ms n=994 Participants	77 ms n=1993 Participants

PRIMARY outcome

Timeframe: Obtained from a test administered approximately 90 minutes after entering the classroom

This is a measure related to attentiveness that is calculated as hit reaction time standard error for correct responses (HRT-SE). A higher HRT-SE indicates highly variable reactions during the ANT test that is related to inattentiveness. A lower HRT-SE indicates indicates consistent reaction times and thus, a better attention performance.

Outcome measures

Outcome measures
Measure	Purified Air n=999 Participants Purifying the air with a Pure Airbox device (Zonair 3D). Use of air purifier (Pure Airbox, Zonair 3D) in the classroom 30 minutes before the participants enter the room and during the 2 hours of the experiment. Purifying the air with a Pure Airbox device (Zonair 3D): Purifying the air of the classroom where the experiment is conducted using a Pure Airbox device (Zonair 3D)	Normal Air n=994 Participants Using a sham air purifier (same device without filters). Use of the same air purifier but without filters, so that it only recirculates the air without purifying it. Used for the same time period than the other arm. Using a sham air purifier (same device without filters): Use the air purifier (Pure Airbox, Zonair 3D) without filters in the classroom where the experiment is conducted
Response Speed Consistency Throughout the Attention Network Task-Flanker Task (Post ANT)	161.3 ms Interval 112.7 to 232.4	160.2 ms Interval 112.4 to 234.7

PRIMARY outcome

Timeframe: Obtained from a test administered approximately 100 minutes after entering the classroom

The "Combined risk taking score" measures how willing the person is to take risks and is calculated as 0.4729985 × "Risk preference score" + 0.5270015 × "Willingness to take risks", as defined in Falk et al (2018). The "Combined risk taking score" is a weighted average of two z-scores ("risk preference score" and "willingness to take risks" score), and therefore it can be interpreted as a z-score. The central value of "Combined risk taking score" is 0 and represents the population mean. The higher the values of the "Combined risk taking score", the more willing is the person to take risks. The "Risk preference score" is the final node in the risk tree (see the online appendix of Falk et al (2018)), which is a value between 1 and 32, ranked by the level of risk aversion, which was then transformed to a z-score. The "Willingness to take risks" refers to the answer to the question on one's willingness to take risks, with values from 0 to 10), which was then transformed to a z-score.

Outcome measures

Outcome measures
Measure	Purified Air n=1068 Participants Purifying the air with a Pure Airbox device (Zonair 3D). Use of air purifier (Pure Airbox, Zonair 3D) in the classroom 30 minutes before the participants enter the room and during the 2 hours of the experiment. Purifying the air with a Pure Airbox device (Zonair 3D): Purifying the air of the classroom where the experiment is conducted using a Pure Airbox device (Zonair 3D)	Normal Air n=1054 Participants Using a sham air purifier (same device without filters). Use of the same air purifier but without filters, so that it only recirculates the air without purifying it. Used for the same time period than the other arm. Using a sham air purifier (same device without filters): Use the air purifier (Pure Airbox, Zonair 3D) without filters in the classroom where the experiment is conducted
Combined Risk Taking Score	-0.0210 Z-score Interval -0.473 to 0.4552	-0.0121 Z-score Interval -0.458 to 0.4738

PRIMARY outcome

Timeframe: Obtained from a test administered approximately 100 minutes after entering the classroom

The "Combined patience score" measures the patience of the person and is calculated as 0.7115185 × "Time preference score" + 0.2884815 × "Self assessment of patience", as defined in Falk et al (2018). The "Combined patience score" is a weighted average of two z-scores ("time preference score" and "self assessment of patience" score), and therefore it can be interpreted as a z-score. The central value of "Combined patience score" is 0 and represents the population mean. The higher the values of the "Combined patience score" the more patience the person has. The "Time preference score" was obtained from the final node in the time tree (see the online appendix of Falk et al (2018)), which is a value between 1 and 32, ranked by the level of patience, which was then transformed to a z-score. The "Self assessment of patience" score refers to the answer to the question on the self-assessment of patience, with values from 0 to 10, which was then transformed to a z-score.

Outcome measures

Outcome measures
Measure	Purified Air n=1068 Participants Purifying the air with a Pure Airbox device (Zonair 3D). Use of air purifier (Pure Airbox, Zonair 3D) in the classroom 30 minutes before the participants enter the room and during the 2 hours of the experiment. Purifying the air with a Pure Airbox device (Zonair 3D): Purifying the air of the classroom where the experiment is conducted using a Pure Airbox device (Zonair 3D)	Normal Air n=1054 Participants Using a sham air purifier (same device without filters). Use of the same air purifier but without filters, so that it only recirculates the air without purifying it. Used for the same time period than the other arm. Using a sham air purifier (same device without filters): Use the air purifier (Pure Airbox, Zonair 3D) without filters in the classroom where the experiment is conducted
Combined Patience Score	-0.1453 Z-score Interval -0.6474 to 0.633	-0.0732 Z-score Interval -0.6516 to 0.6575

PRIMARY outcome

Timeframe: Obtained from a test administered approximately 100 minutes after entering the classroom

The "Positive reciprocity score" measures positive reciprocity. A person with high reciprocity agrees with the statement "When someone does me a favor, I am willing to return it". The score is calculated as 0.4847038 × "Willingness to return favor" + 0.5152962 × "Size of gift", as defined in Falk et al (2018). The "Positive reciprocity score" is a weighted average of two z-scores ("willingness to return a favor" score and "size of gift" score), and therefore it can be interpreted as a z-score, with the central value of 0 representing the population mean. Higher values of the score imply more positive reciprocity. "Willingness to return favor" refers to the answer to the question on the willingness to return a favor, ranked from 0 to 10 and then transformed to a z-score. "Size of gift" refers to the answer to the question on the reported size of the gift that would return to a stranger, from a list of 7 possible values (from 0 to 30€, by 5€ steps), then transformed to a z-score.

Outcome measures

Outcome measures
Measure	Purified Air n=1068 Participants Purifying the air with a Pure Airbox device (Zonair 3D). Use of air purifier (Pure Airbox, Zonair 3D) in the classroom 30 minutes before the participants enter the room and during the 2 hours of the experiment. Purifying the air with a Pure Airbox device (Zonair 3D): Purifying the air of the classroom where the experiment is conducted using a Pure Airbox device (Zonair 3D)	Normal Air n=1054 Participants Using a sham air purifier (same device without filters). Use of the same air purifier but without filters, so that it only recirculates the air without purifying it. Used for the same time period than the other arm. Using a sham air purifier (same device without filters): Use the air purifier (Pure Airbox, Zonair 3D) without filters in the classroom where the experiment is conducted
Positive Reciprocity Score	-0.0186 Z-score Interval -0.3644 to 0.5352	-0.0359 Z-score Interval -0.5999 to 0.5372

PRIMARY outcome

Timeframe: Obtained from a test administered approximately 100 minutes after entering the classroom

The "Altruism score" measures the altruism of a person and is calculated as 0.6350048 × "Willingness to give to good causes" + 0.3649952 × "Hypothetical donation", as defined in Falk et al (2018). The "Altruism score" is a weighted average of two z-scores ("willingness to give to good causes" score and "hypothetical donation" score), and therefore it can be interpreted as a z-score, with the central value of 0 representing the population mean. Higher values of the score imply more altruism. "Willingness to give to good causes" refers to the answer to the question on the willingness to give to good causes, ranked from 0 to 10 and then transformed to a z-score. "Hypothetical donation" refers to the answer to the question on the size of the hypothetical donation one would be willing to make, transformed to a z-score.

Outcome measures

Outcome measures
Measure	Purified Air n=1068 Participants Purifying the air with a Pure Airbox device (Zonair 3D). Use of air purifier (Pure Airbox, Zonair 3D) in the classroom 30 minutes before the participants enter the room and during the 2 hours of the experiment. Purifying the air with a Pure Airbox device (Zonair 3D): Purifying the air of the classroom where the experiment is conducted using a Pure Airbox device (Zonair 3D)	Normal Air n=1054 Participants Using a sham air purifier (same device without filters). Use of the same air purifier but without filters, so that it only recirculates the air without purifying it. Used for the same time period than the other arm. Using a sham air purifier (same device without filters): Use the air purifier (Pure Airbox, Zonair 3D) without filters in the classroom where the experiment is conducted
Altruism Score	0.1118 Z-score Interval -0.5652 to 0.6197	0.0597 Z-score Interval -0.6023 to 0.6754

PRIMARY outcome

Timeframe: Obtained from a test administered approximately 100 minutes after entering the classroom

Answer to the question "I assume that people have only the best intentions", which is ranked from 0 to 10. Higher values imply more trust.

Outcome measures

Outcome measures
Measure	Purified Air n=1068 Participants Purifying the air with a Pure Airbox device (Zonair 3D). Use of air purifier (Pure Airbox, Zonair 3D) in the classroom 30 minutes before the participants enter the room and during the 2 hours of the experiment. Purifying the air with a Pure Airbox device (Zonair 3D): Purifying the air of the classroom where the experiment is conducted using a Pure Airbox device (Zonair 3D)	Normal Air n=1054 Participants Using a sham air purifier (same device without filters). Use of the same air purifier but without filters, so that it only recirculates the air without purifying it. Used for the same time period than the other arm. Using a sham air purifier (same device without filters): Use the air purifier (Pure Airbox, Zonair 3D) without filters in the classroom where the experiment is conducted
Trust Score	5 score on a scale Interval 4.0 to 7.0	5 score on a scale Interval 4.0 to 7.0

SECONDARY outcome

Timeframe: Obtained from a test administered approximately 90 minutes after entering the classroom

Number of incorrect responses (responses made in the opposite direction to the direction of the target arrow) Lower score indicates a better attention performance. Total range score: 0-38.

Outcome measures

Outcome measures
Measure	Purified Air n=999 Participants Purifying the air with a Pure Airbox device (Zonair 3D). Use of air purifier (Pure Airbox, Zonair 3D) in the classroom 30 minutes before the participants enter the room and during the 2 hours of the experiment. Purifying the air with a Pure Airbox device (Zonair 3D): Purifying the air of the classroom where the experiment is conducted using a Pure Airbox device (Zonair 3D)	Normal Air n=994 Participants Using a sham air purifier (same device without filters). Use of the same air purifier but without filters, so that it only recirculates the air without purifying it. Used for the same time period than the other arm. Using a sham air purifier (same device without filters): Use the air purifier (Pure Airbox, Zonair 3D) without filters in the classroom where the experiment is conducted
Impulsivity (From ANT)	2 total score Interval 1.0 to 4.0	2 total score Interval 1.0 to 4.0

SECONDARY outcome

Timeframe: Obtained from a test administered approximately 90 minutes after entering the classroom

Number of omission errors (failure to respond) Lower score indicates a better attention performance Total range score: 0-21. Higher values represent a worse outcome

Outcome measures

Outcome measures
Measure	Purified Air n=999 Participants Purifying the air with a Pure Airbox device (Zonair 3D). Use of air purifier (Pure Airbox, Zonair 3D) in the classroom 30 minutes before the participants enter the room and during the 2 hours of the experiment. Purifying the air with a Pure Airbox device (Zonair 3D): Purifying the air of the classroom where the experiment is conducted using a Pure Airbox device (Zonair 3D)	Normal Air n=994 Participants Using a sham air purifier (same device without filters). Use of the same air purifier but without filters, so that it only recirculates the air without purifying it. Used for the same time period than the other arm. Using a sham air purifier (same device without filters): Use the air purifier (Pure Airbox, Zonair 3D) without filters in the classroom where the experiment is conducted
Selective Attention (From ANT)	0 total score Interval 0.0 to 0.0	0 total score Interval 0.0 to 0.0

SECONDARY outcome

Timeframe: Obtained from a test administered approximately 90 minutes after entering the classroom

Alerting represents the ability to maintain a state of high vigilance to incoming stimuli It is calculated by subtracting the median reaction time for double cue from median reaction time for the no cue condition (calculations performed after removing the incongruent trials). A lower score indicates a better attention performance

Outcome measures

Outcome measures
Measure	Purified Air n=999 Participants Purifying the air with a Pure Airbox device (Zonair 3D). Use of air purifier (Pure Airbox, Zonair 3D) in the classroom 30 minutes before the participants enter the room and during the 2 hours of the experiment. Purifying the air with a Pure Airbox device (Zonair 3D): Purifying the air of the classroom where the experiment is conducted using a Pure Airbox device (Zonair 3D)	Normal Air n=994 Participants Using a sham air purifier (same device without filters). Use of the same air purifier but without filters, so that it only recirculates the air without purifying it. Used for the same time period than the other arm. Using a sham air purifier (same device without filters): Use the air purifier (Pure Airbox, Zonair 3D) without filters in the classroom where the experiment is conducted
Alerting Score (From ANT)	42 ms Interval 18.0 to 68.5	44.5 ms Interval 17.0 to 73.0

SECONDARY outcome

Timeframe: Obtained from a test administered approximately 90 minutes after entering the classroom

Orienting is the ability to select information and it is calculated by subtracting the median reaction time for spatial cue from the reaction time for central cue (calculations performed after removing the incongruent trials).A lower score indicates a better attention performance

Outcome measures

Outcome measures
Measure	Purified Air n=999 Participants Purifying the air with a Pure Airbox device (Zonair 3D). Use of air purifier (Pure Airbox, Zonair 3D) in the classroom 30 minutes before the participants enter the room and during the 2 hours of the experiment. Purifying the air with a Pure Airbox device (Zonair 3D): Purifying the air of the classroom where the experiment is conducted using a Pure Airbox device (Zonair 3D)	Normal Air n=994 Participants Using a sham air purifier (same device without filters). Use of the same air purifier but without filters, so that it only recirculates the air without purifying it. Used for the same time period than the other arm. Using a sham air purifier (same device without filters): Use the air purifier (Pure Airbox, Zonair 3D) without filters in the classroom where the experiment is conducted
Orienting Score (From ANT)	12.5 ms Interval -11.5 to 39.0	13.5 ms Interval -11.5 to 37.5

SECONDARY outcome

Timeframe: Obtained from a test administered approximately 90 minutes after entering the classroom

Conflict generally refers to the ability to monitor and resolve conflict among responses and in this study it is calculated as the median reaction time for each flanker condition (across cue conditions) and subtracting the congruent from the incongruent reaction times. A lower score indicates a better attention performance

Outcome measures

Outcome measures
Measure	Purified Air n=999 Participants Purifying the air with a Pure Airbox device (Zonair 3D). Use of air purifier (Pure Airbox, Zonair 3D) in the classroom 30 minutes before the participants enter the room and during the 2 hours of the experiment. Purifying the air with a Pure Airbox device (Zonair 3D): Purifying the air of the classroom where the experiment is conducted using a Pure Airbox device (Zonair 3D)	Normal Air n=994 Participants Using a sham air purifier (same device without filters). Use of the same air purifier but without filters, so that it only recirculates the air without purifying it. Used for the same time period than the other arm. Using a sham air purifier (same device without filters): Use the air purifier (Pure Airbox, Zonair 3D) without filters in the classroom where the experiment is conducted
Conflict Score (Executive Attention) (From ANT)	75 ms Interval 57.5 to 93.5	75 ms Interval 58.0 to 95.5

SECONDARY outcome

Timeframe: Obtained from a test administered approximately 100 minutes after entering the classroom

Answer to the question on math skills, ranging from 0 to 10. The higher the score, the better the person feels s/he is doing in math.

Outcome measures

Outcome measures
Measure	Purified Air n=746 Participants Purifying the air with a Pure Airbox device (Zonair 3D). Use of air purifier (Pure Airbox, Zonair 3D) in the classroom 30 minutes before the participants enter the room and during the 2 hours of the experiment. Purifying the air with a Pure Airbox device (Zonair 3D): Purifying the air of the classroom where the experiment is conducted using a Pure Airbox device (Zonair 3D)	Normal Air n=767 Participants Using a sham air purifier (same device without filters). Use of the same air purifier but without filters, so that it only recirculates the air without purifying it. Used for the same time period than the other arm. Using a sham air purifier (same device without filters): Use the air purifier (Pure Airbox, Zonair 3D) without filters in the classroom where the experiment is conducted
Self Assessment of How Good They Are in Math	6 score on a scale Interval 3.0 to 8.0	6 score on a scale Interval 3.0 to 8.0

Adverse Events

Purified Air

Serious events: 0 serious events

Other events: 0 other events

Deaths: 0 deaths

Normal Air

Serious events: 0 serious events

Other events: 0 other events

Deaths: 0 deaths

Serious adverse events

Adverse event data not reported

Other adverse events

Adverse event data not reported

Additional Information

Dr. Xavier Basagaña

Barcelona Institute for Global Health (ISGlobal)

Phone: (+34) 93 214 7306

Email: [email protected]

Results disclosure agreements

Principal investigator is a sponsor employee
Publication restrictions are in place