I've been looking at some air quality monitoring results for ozone and trying to understand why there is such difference between locations. Near busy roads, the sea, near factories?

I am quite confused though!

Salford monitoring - the monitor is situated 20meters next to a motorway (M60) and near some other large roads and junctions. It has a yearly average of 31 (fairly low).

London generally has very low ozone (21, 25, 30, 32, 38, 45, 48) so does Manchester Picadilly (29)

Sibton in Norfolk has high Ozone, it is far away from busy roads, 11km away from the sea and in a very rural area (58).

Birmingham Acocks Green also has high Ozone (51), it is far away from the sea, 134m altitude (fairly high for UK towns!) and in the suburbs, 500m away from a medium A road.

There seems to be a bit of a correlation between the sea but not from traffic even though everyone says it is NO2 from traffic that causes ozone.

Even though London seems fairly low the results are strange too, Kensington has 48 but Marylebone 22 (only 4km away from each other). Tower Hamlets Millwall Park near a park and the thames is 45 but Tower Hamlets Blackwall next to a busy road is 25 (and they are just 2.9km apart).

  • I do wonder how accurate these values actually are. Possibly you just need a combination and just one element, such as NO2 on its own won't do anything. Maybe VOCs disperse more quickly than NO2 so the NO2 has to move towards the VOC emissions and maybe damp air can be blown from far distances. It still doesn't explain Marylebone and Kensington and Hammersmith differences though. Maybe it is just complicated! but then that might mean this monitoring could be a bit pointless!
    – atreeon
    Feb 24, 2020 at 22:37
  • 1
    Can you provide your source for this data, and/or a map of the locations?
    – LShaver
    Feb 25, 2020 at 14:51
  • High ozone in urban situations is usually, I believe, the result of a photochemical smog ... which occurs during prolonged dry and sunny conditions when photochemical reactions (i.e chemical reactions which take place with the help of sunlight) produce a range of chemicals, including ozone. My guess is that your "generally low" ozone levels come from normal days when there is a fresh wind blowing into the city. As LShaver says, you need to give more details about where these numbers come from.
    – M Juckes
    Feb 26, 2020 at 22:48

1 Answer 1


In what type of location is it likely to find larger or smaller amounts of ozone?

Using data from the 2017 Tropospheric Ozone Assessment Report we can answer the first part of the question. There's a massive database of images and plots available, from which I pulled just a few.

Here's a full image to include the legend and caption:

50th percentile ozone value, annual average 2010 to 2014

Now I'll focus just on the UK since that's what you've asked about. From left to right:

  • Rural, high elevation sites
  • Rural, low elevation sites
  • Urban sites
  • Non-urban sites

50th percentile ozone value, annual average 2010 to 2014, UK

Based on these maps, the higher concentrations appear to be in rural, coastal sites. There is only one high-elevation site in the UK, but it also has a higher relative concentration, consistent with high-elevation sites in other countries.

Why is the concentration different between locations?

According to Wikipedia:

Motor vehicle exhaust, industrial emissions, and chemical solvents are the major anthropogenic sources of these ozone precursors. Although the ozone precursors often originate in urban areas, winds can carry NOx hundreds of kilometers, causing ozone formation to occur in less populated regions as well.

In the UK, the prevailing winds are from the south and west (source), and population is densest roughly in the south and east:

Night-time map of the UK

This means we'd expect to see ozone concentrations roughly north and east of population centers, which is consistent with the maps.

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