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One of the largest Australian studies of classroom air quality conducted in the state’s public schools has revealed almost a third recorded carbon dioxide levels not considered optimal for students’ learning “most of the time”.
The University of NSW report measured air quality at 59 schools across Sydney, Newcastle and Wollongong and found 17 school classrooms experienced carbon dioxide levels beyond what is recommended by the Commonwealth government’s National Construction Code.
The air quality findings, which were quietly uploaded to a NSW Department of Education website this year, have triggered calls for air quality monitoring in all schools while researchers say the installation of mechanical ventilation systems needs to be prioritised.
While 17 schools had high carbon dioxide levels “most of the time”, the authors said most school classrooms recorded levels which exceeded the guidelines of 850 parts per million. However, those levels were typically short-lived.
Three schools – Condell Park High and Hebersham Public in Sydney and Mayfield East Public in Newcastle – experienced levels above 1000 parts per million for most of the school day, the report said.
“In summary, there is some evidence that indoor CO₂ levels in NSW classrooms we tested are exceeding levels optimal for students’ learning and health,” the report said.
Air quality data was collected over 2024 and 2025 as part of the Clean Air Schools Program. While it was a large study, the authors said it was limited because air quality was measured in a single classroom.
Researchers collected air quality data by installing sensors in one classroom at each of the schools, taking carbon dioxide readings every 30 minutes.
A Department of Education spokesman would not provide a list of the 17 schools with carbon dioxide levels above what was recommended, but said there was no threat to safety.
“Students and their families can be assured that the report did not state that any classrooms in NSW public schools were unsafe,” he said.
“UNSW stated that it did not see the levels of [nitrogen dioxide] that pose a serious risk to children in its data and most classrooms did not exceed the [carbon dioxide] threshold between teaching hours.”
He said the department is now working with independent hygienists to “undertake targeted follow-up assessment and will follow their recommendations”.
The University of NSW report found cross-ventilated classrooms had lower average carbon dioxide levels.
The researchers distinguished between Cooler Classrooms schools, which were part of a large government program which installed ducted air conditioning at hundreds of schools and those schools which had just a split system. Schools with the ducted system typically had lower carbon dioxide levels.
The study also measured levels of particulate matter, which it said was low, noting that when the testing was carried out in 2024 and 2025, there were few extreme weather events such as dust storms or bushfires.
Outside in school playgrounds, sensors measured levels of nitrogen dioxide every 15 minutes.
Five out of 27 schools whose nitrogen dioxide levels were measured in the study were found to have concentrations which breached the NSW hourly threshold of 80 parts per billion.
“While a significant number of schools exceeded the average yearly threshold, concern from NO2 exposure typically comes from short-term exposure to high levels,” it said.
Georges River College Penshurst Girls Campus was singled out for having outdoor nitrogen dioxide levels which were “well above” the yearly threshold, which the report authors said could be due to nearby roads, construction and industrial pollution.
NSW Greens MP Dr Amanda Cohn, who chairs the Clean Indoor Air inquiry, said it was concerning that almost one-third of classrooms tested had unsafe levels of carbon dioxide, a key indicator of poor ventilation.
“How many other classrooms are unsafe, but not even being monitored? Widespread air quality monitoring is clearly required as well as a systematic approach to fixing ventilation in schools,” she said.
She said parents and teachers had the right to know if the air students and staff were breathing in for hours every day was a risk to their health.
“Not only is poor air quality in these classrooms impacting students’ capacity to focus and learn, it poses a dangerous risk to some kids who have existing health conditions,” she said.
She said it was “not good enough” to tell teachers to shut windows. “Noise, weather and outdoor air pollution are all reasons that windows are closed, and why air quality monitoring and mechanical ventilation systems are necessary,” she said.
The department provided updated ventilation advice to schools during the first term of 2026.
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