Londoners breathe significantly cleaner air when exercising at weekends, according to new research showing nitrogen dioxide (NO₂) exposure falling by almost 25% compared with weekdays.
The study, based on over 50,000 outdoor runs, rides and walks logged across the capital between March 2024 and August 2025 – appears to reveal that median NO₂ exposure drops from 32 µg/m³ on weekdays to 24 µg/m³ on weekends.
The data has been provided by technology firm Air Aware Labs.
Whilst this weekend reduction sits just beneath the World Health Organization’s short-term air pollution guideline of 25 µg/m³ for a 24-hour period, it’s still dangerously close to the recommended healthy air values – which are increasingly subject to individual behaviour, as well as variations due to changes in traffic volumes, hotter temperatures and meteorological factors like wind direction.
Key findings:
- Clean-air weekends: 19 of London’s boroughs fall beneath the WHO NO₂ reference value at weekends, compared with just four on weekdays
- Borough contrasts: Camden records the largest improvement (-31%), while Lambeth saw the worst weekday levels (38.1 µg/m³). Merton offered the cleanest weekend air (17.0 µg/m³).
- Borough outliers: Hounslow (+11%) and Havering (+9%) buck the trend, with higher weekend NO₂ likely linked to airport and corridor traffic.
- When you exercise matters: The workouts with the lowest exposure are around 5am (18 µg/m³), while pollution exposure peaks close to 11pm (40 µg/m³).
- Traffic-linked impact: Data suggests underlying traffic-linked NO₂ is the dominant driver of exposure between weekdays vs weekends in the capital.
Air pollution costs the UK £500m a week in ill health, and across 2024 in London alone, 114,000 children were admitted to A&E with serious breathing problems – the equivalent of every seat in Wembley Stadium filled one and a half times over.
Unlike ambient monitoring, AirTrack analysis reflects real-world personal exposure from the more than 50,000 logged activities that have been undertaken in the capital as part of this study.
Dr Will Hicks, co-founder, Air Aware Labs, said:
“Air pollution remains the biggest environmental health risk of our time, and this evidence shows it’s not just background air quality but individual behaviour that results in dangerous weekday commuter exposure.
“These findings strengthen the case for targeted measures like clean-air zones during peak commuting hours and borough-level interventions where the health returns are greatest. But we need to move beyond generic advice to real-time, personalised action if we’re serious about protecting Londoners’ health.
WHO guidelines are designed to safeguard health. Think of exposure like bad credit card debt: even small amounts come at a cost, but the bigger the balance, the steeper the penalty. The safest balance is zero. And just as financial debt takes discipline to reduce, cutting air pollution demands determination from both individuals and government.”
The findings coincide with the capital being put on a high air pollution alert during the recent hot temperatures and land just as London debates clean-air corridors, ULEZ expansion and peak-hour interventions.
It has also been announced that Oxford Street is to go car-free for a day on Sunday 21 September – the day before World Car Free Day – to demonstrate how pedestrianisation could work, if the Mayor of London’s plans go ahead.
