Since Enfield’s first low traffic neighbourhood went in we have been following the air quality monitoring station at Bowes school. Some people were concerned that air quality would deteriorate due to more traffic on the A406 – this was a worry as the monitoring station is in the school grounds. We were confident this wouldn’t happen, but it seemed sensible to wait for the trial to progress before drawing any conclusions. However, in the recent opposition report, there was some ‘cherry-picked’ data to show that the LTNs had caused air pollution to go up. ‘Cherry-picked’ data because air pollution always goes up in the winter for various reasons* – so a month by month comparison isn’t particularly useful or valid.

Thanks to Viola Rondeboom‘s description and her husband Hado’s clever graphs we can illustrate what really happened to air quality since the LTN went fully operational (12th September 2020)

Viola writes:

With a primary school situated on Bowes Road, A406 North Circular, which is one of the boundary A-roads of our LTN, we’ve kept a watchful eye on the Bowes pollution monitor. Here’s what we found. The first graph shows the monthly averages of NO2 from August-December 2020 compared to previous years.

There are three things worth noting, let’s start with the first two: 1. Every year pollution gets worse in winter. This is a normal seasonal trend. 2. Pollution after the LTN was introduced (12 Sept) was less than usual. However, in November something unusual happened: on the first Wednesday (4/11), tens of thousands of people got into their cars to flee London before a second national lockdown, announced four days before, came into force. The result: carnage on London roads everywhere…

Which leads to our last observation: 3. This terrible traffic caused a large spike in pollution levels, which also increased the monthly average for November. This is visible when looking at the data in more detail. Here are weekly averages of the same period: Graph 2.

The subsequent week pollution levels went back to pre-lockdown levels, which shows the spike cannot be attributed to the LTN.Conclusion: There is no evidence in the data for a detrimental effect of the LTN on pollution levels. However, with the LTN only implemented four and half months ago, we think it’s important to continue to carefully monitor this data.

Plots are our own, we used data from Londonair

For the final point and for the avoidance of doubt, I have included an extra graph which shows a comparison of another Enfield school for the same period over November (Prince of Wales School). It shows the same spike caused by the start of lockdown. Actually, both monitoring stations track each other reasonably well, but the Prince of Wales School is impacted by the M25 rather than the A406.

Not such a pretty graph but this one drawn by the Londonair website

All the information on the Londonair website is public and allows you to play around with graphs, download data etc. – so anyone can check what is going on with pollution levels around London.

Hal Haines

†*For those interested in air monitoring further information can be found here.