London’s NO2 Readings - What Do the Figures Reveal?

March 26, 2018

The recently released Mercer 2018 Quality of Living City Rankings listed London only in the 67th place for sanitation. The sanitation rankings are based on multiple criteria including the city’s air pollution, sewage, waste removal, water quality and availability, and infectious disease. Despite that, the Mercer says London is ranked so low mainly due to “persistent air pollution and traffic congestion”. London Cleaning System company therefore decided to investigate whether London’s air is really so bad.

Official Figures for Air Pollution Encouraging but NO2 Remains a Major Concern

Looking at official data on air pollution in London, the company researchers found that air quality in the UK capital has improved significantly over the recent years, with the city authorities reassuring the residents that most of the most dangerous pollutants are not "at levels that affect human health”. On the other hand, the city authorities also admit that some air pollutants remain a concern including nitrogen dioxide (NO2) which, according to the 2015 study by King’s College London, was responsible for an estimated 5,900 premature deaths in London in 2010. The levels of the harmful gas dropped significantly since then but in 2018, the UK capital exceeded the EU yearly maximum for NO2 as early as the end of January.

Monthly NO2 Averages Within “Low” Index but Levels Vary Greatly by Time of Day

To find out more about NO2 pollution, London Cleaning System company decided to further analyse the official data, looking back as far as 2010 when longterm exposure to the harmful gas was blamed for nearly 6,000 premature deaths. The company’s researchers noticed that while NO2 monthly average levels at roadside were considerably higher than in background, they didn’t exceed the “low” index level not even once by January 2018. But time of day charts revealed that NO2 levels vary greatly during the day and most importantly, always peak at the same time of the day.

NO2 Levels Always Highest During Morning and Afternoon Rush Hours

Charts presenting NO2 concentrations in London at different time of day in January 2018 show a very predictable pattern. The levels begin to rise just before the morning and afternoon rush hours, and peak around 8 to 9am and 5 to 6pm. Just like the monthly averages, the NO2 concentrations are higher at roadside than in background at all times of the day. Despite that, they remained within “low" index level, reaching a maximum of 60.3 ug/m3.

This is considerable improvement since January 2016 when NO2 levels reached 75 ug/m3 or more during both morning and afternoon rush hours. Decrease of NO2 levels was also observed in London background, dropping from 50.9 ug/m3 that was a maximum measured in January 2016 to slightly above 40 ug/m3 as much was the maximum mean reading in January 2018.

Why are the Results of NO2 Readings During Rush Hours Important?

Readings of NO2 concentrations during morning and afternoon hours are important for two reasons. First, they provide strong evidence that traffic is the main source of NO2 pollution. This means that cutting the number of dirty vehicles, which is the main strategy of the city authorities to tackle the problem, will bring further improvement in NO2 pollution levels - of course, if successful. And second, it means that Londoners who are living at roadside, especially those living along the most congested roads, should keep their windows closed during the morning and afternoon rush hours to minimise the risk of respiratory diseases and other health problems associated with NO2 pollution.