Air pollution in Crystal Palace

This blog provides data and information about air pollution levels in Crystal Palace, where I live. Like many urban places it suffers from high levels of air pollution, which has a significant impact on our health.

Nitrogen Dioxide pollution is bad for our health. It reduces life expectancy, and makes lung and heart conditions worse. The government’s Committee on the Medical Effects of Air Pollutants (COMEAP) estimates that between 28,000 and 36,000 people die as a result of all forms of air pollution every year in the UK.

There was a lot of local concern about air pollution after Croydon Council introduced its ‘Low Traffic Neighbourhood’ policy. This blog post doesn’t pass any comment on the policy, but I hope helps people to discuss policies armed with the available facts.

There are two sections to this post:

  1. Monitoring conducted by Bromley Council on Anerley Hill. This shows pollution levels on this road in each month of 2020 compared to previous years.
  2. Tables of and maps data from citizen science monitoring. These give an indication of the relative levels of pollution in different locations over three different periods in 2014 and 2021.

Both present information on Nitrogen Dioxide (NO2) levels. This gas is one of the main types of air pollution, alongside tiny particulates (PM10 and PM2.5), ozone and others. It’s the easiest to measure, and all the data in this post comes from diffusion tubes, which you can read about here.

The numbers refer to the concentration of Nitrogen Dioxide (NO2) in the air, measured in micrograms of NO2 per meter cubed (µg/m3).

The figures are averages over a month. So they don’t capture spikes, for example whether there’s a short-term problem at school drop-off and pick-up times.

Anerley Hill

Bromley Council monitors Nitrogen Dioxide levels at the same location on Anerley Hill each month, and publishes the results in its air quality annual status reports. They use three diffusion tubes each time and take an average of the three, to improve accuracy.

This is the only location in Crystal Palace regularly monitored by anyone. None of the four other councils have monitoring sites in the area. There used to be a much more sophisticated live monitoring station on Crystal Palace Parade but it was defunded and closed some years ago.

There is a gap in the results for 2020, as the council suspended monitoring during the first lockdown.

This first chart shows the monthly results for the past six years, including 2020.

Some things you can observe from this:

  • The numbers bump around a lot, but are generally higher over the winter and lower over the summer holidays.
  • Readings often exceed the legal limit of 40 (μg/m3).

This second chart compares 2020 to the five year average over 2015-2019, so you can more clearly see how the year compared to the past five years. Significant dates in that year to bear in mind are:

  • Lockdown 1 – March to late June
  • Lockdown 2 – Nov to early Dec
  • Low Traffic Neighbourhood – August to end of year (and into 2021)

Some things you can take away from this chart:

  • Pollution levels in the latter half of 2020 were not significantly higher or lower than previous years.
  • The red line is a little below the blue line in the last few months, but given how bumpy the results are from one year to the next this doesn’t suggest the end of 2020 was out of the ordinary.
  • The data doesn’t tell us what impact, if at all, the lockdowns and LTN had. But the combined effect was clearly to leave 2020 much like other years – high levels of pollution.

Citizen science

I led three rounds of air pollution measurement using diffusion tubes, in July 2014, March/April 2021 and June/July 2021.

The two rounds in 2021 were funded by 18 wonderful individuals through a crowdfunder, and both the donors and the people who carried out the subsequent monitoring work have a variety of views on the Croydon LTN – pro, anti and neutral.

The results are less reliable than those from Bromley Council, but still valid. We only used one tube per location, and the results are not ratified through the official process. But we followed the same guidelines as councils to locate the tubes, and used accredited labs to analyse the tubes – Kings College London in 2014, and Staffordshire Council in 2021.

This table shows the results for 22 locations. I’ve not included some others in 2014, which can be seen in the map below. The table focuses on the spread across the wider area that we went for in 2021.

There are a few gaps because people stole the tubes! We put a tube up on Milestone Road in spring 2021 but it was nicked; the tube on Harold Road / Vermont Road was taken in summer 2021; a tube I put outside Rockmount School in 2014 was taken. Goodness knows why.

The colour coding in this table helps to understand the meaning of the numbers:

  • Green – below 20 µg/m3 and not really unhealthy
  • Yellow – above a safe level, but below the legal limit of 40 µg/m3
  • Red – above the legal limit of 40 µg/m3
  • Dark red – over 60 µg/m3, far above the legal limit

It’s not really possible to talk of ‘safe’ or ‘healthy’ levels of air pollution – all pollution is bad. But preventable deaths would be far fewer and other health problems would be far less bad if average levels we breathed in, day in and day out, were below 20 µg/m3.

UPDATE, Sept 2021: the World Health Organisation is updating its recommendations, so that 10 µg/m3 will become the new limit. That puts every measurement well over what the WHO considers to be unhealthy levels.

Using the same colour coding, these maps show the pollution as measured each time. You can zoom in and pan around.

2014 – summer

2021 – spring

2021 – summer

What next?

What do we do with this information, as citizens? That’s really up to you.

I firmly believe we need to take action to reduce air pollution, and have campaigned for over a decade to achieve that by reducing traffic and cleaning up TfL’s bus fleet. Less traffic would also make a dent in tackling the climate emergency, improve road safety and generally make Crystal Palace a nicer place to live. I hope you take to social media, or cafe tables, to debate ways to achieve that. The status quo – as you can see above – is seriously unhealthy pollution.


  1. Dave Marshall said:

    Interesting post, Tom. I share your view that low frequency monitoring averaging away spikes makes it hard to understand just how bad rush hours are. There is only one high frequency monitor in Bromley Borough and it is at the cleanest of all the monitoring sites (based on NO2 diffusion tube data).

    One question – what’s your source for the 2020 Anerley Hill NO2 diffusion tube data? The 2020 annual report hasn’t been released yet.

    25th August 2021
    • tomchance said:

      Hi Dave,

      The 2020 Anerley Hill data is from Bromley Council’s report, which they kindly shared with me ahead of publication on their website.


      26th August 2021

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