Levels of nitrogen dioxide (NO₂) exceeding World Health Organization (WHO) guidelines have been found in hotspots across Dublin city, according to a new study.

Data collected by University College Dublin and Dublin City University (DCU) researchers shows high levels of NO₂ and fine particulate matter (PM_2.5) across Dublin’s inner city.

Areas of particularly high concentrations included Cork Street, O’Connell Street, along the Quays, and in the area around Temple Bar.

The data showed that during the sampling period, 49.4% of days exceeded WHO guidelines for NO₂ levels, with peaks during rush hours, especially in winter. The findings are published in the journal Environmental Science and Pollution Research.

Collected as part of the Google Air View project over a period of 16 months, using electric Google Street View cars equipped with air sensors, the data showed that during the sampling period, almost 50% of days exceeded WHO guidelines for NO₂ levels, with peaks during rush hours, especially in winter.

Carried out by Dr. Jiayao Chen, Dr. Anna Mölter, Dr. José Pablo Gómez-Barrón and Professor Francesco Pilla, UCD’s School of Architecture, Planning and Environmental Policy, and Dr. David O’Connor from DCU’s School of Chemical Sciences, the study suggests the potential of a mobile monitoring approach to investigating hyperlocal air pollutants across cities.

“Traffic pollution is a critical issue in urban cities, often contributing to or exacerbating environmental or social-economic inequalities,” said Dr. Chen.

“Our finding represents a unique case for Dublin—on highly polluted days, domestic heating emerged as the dominant contributor to PM_2.5 at street level. Our research emphasizes the need for detailed temporal guidance, especially for vulnerable populations, to help guide safe indoor and outdoor activities.

“With the EU recently introducing stricter air quality guidelines, our findings underscore the need for long-term, localized monitoring to inform strategic mitigation plans tailored to both local and regional scales.”

Dr. O’Connor added, “As more cities adopt hyperlocal sensing, the potential to create healthier urban environments grows. Localized air quality data provides the foundation for tailored, evidence-based policy solutions that can tackle pollution at its source, particularly in high-risk and vulnerable areas.”

Study pinpoints ‘hotspots’ of harmful air pollutant in Dublin