Trends in annual averages |
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Supplementary charts Indicative average concentrations of NO2 and PM2.5 - and their variation throughout the day (as measured using an EarthSense Zephyr funded by Westminster City Council)
 Annual average concentrations from NO2 diffusion tubes (for the most recent 12 months as at January 2024) Source: Westminster City Council, Citzen Science, HS2, Camden Council Remarks: Concentrations in Marylebone tend to exceed those in St John's Wood - greater traffic, commercial property and less green open space contribute to this. (See here for a more detailed analysis of air quality across Marylebone during 2022/3.) Concentrations along arterial roads (notably the A40, A5 A41) considerably exceed those in backgroun locations. Substantially more monitoring in Camden (- but with what consequence?).  Trends in average NO2 concentrations for successive periods of 12 months Source: Air Quality England and London Air (* busy roadside, ** quiet, background site) Remarks: Introduction and extension of the Low and Ultra Low emission zones explains much of the reduction in air pollution from NO2 which occured during periods of a year or so either side of official covid-related constraints. The rate of improvement since then has been slow, implying that further intervention is required - the current UK limit 40 µg/m³ is four times greater than the World Health Organisation guideline.  Diurnal variation in average ratified NO2 concentrations - 01/04/2023 to 31/03/2024 Source: Air Quality England (* busy roadside, ** quiet, background site) Remarks: Weekday concentrations exceed those on days off, have a more pronounced morning rush hour peak and an earlier evening peak. The lowest concentrations - best for outdoor exercise - tend to be at lunch time (and 3 am). Data for Wicken Fen (Cambridgeshire) is included for contrast.  Diurnal variation in average ratified PM10 concentrations - 01/07/2022 to 30/06/2023 Source: Air Quality England (* busy roadside, ** quiet, background site) Remarks: Concentrations of PM2.5 tend to vary little not only between the working week and days off, but also with time of day. They exceed the World Health Organisation guideline by a substantial margin. Data for Wicken Fen (Cambridgeshire) is included for contrast.  Trends in average PM2.5 concentrations for successive periods of 12 months Source: Air Quality England and London Air (* quiet, background site) Remarks: Declining concentration of PM2.5 probably attributable to Low and Ultra Low emissions zones prior to and since covid lockdowns. Current trend flat or rising slightly, implying further intervention is required to reduce concentrations adjacent busy roads to below the UK target of 10 µg/m³. Doing so might lessen concentrations in background locations to 50% above the World Health Organisation guideline. |
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