London Air Quality in 2025

London's air improved again in 2025 on paper — roadside nitrogen dioxide has fallen since the ULEZ expanded to cover all boroughs. But two things haven't changed: fine-particle PM2.5 still regularly exceeds World Health Organisation guideline levels, and a large share of outdoor pollution ends up inside our homes.

PM2.5 is the pollutant that matters most for health, and it's only loosely affected by ULEZ because much of it comes from tyre and brake wear, wood burning and sources beyond the city. On a still day it pools at street level and seeps indoors through vents and gaps.

The hotspots

• Euston Road / Marylebone Road — persistently among the UK's worst NO2.
• Inner-city arterials — the A10, A11/A12, South Circular.
• Winter wood-burning — a growing PM2.5 source in residential areas.

What it means for your home

Outdoor improvements are slow and partial; indoor air is something you control today. A high-airflow purifier holds indoor PM2.5 well below outdoor levels, especially overnight. Check your local readings on the London Air Quality Network before airing rooms on calm, sunny days.

How 2025 actually looked, borough by borough

Averaged across the year, the picture is genuinely mixed rather than uniformly better. Central monitoring sites near Euston Road and Marylebone Road still logged some of the highest roadside nitrogen dioxide readings in the country, even as the wider London-wide ULEZ (expanded to the outer boroughs in August 2023) pushed the fleet cleaner. Move outward to the arterial routes — the A10 through Hackney and Tottenham, the A11 and A12 heading east, and the South Circular around Catford and Lewisham — and the same pattern repeats: NO2 tied tightly to traffic volume, dropping on quiet weekends and climbing again with the Monday rush.

Fine-particle PM2.5 behaves differently. It drifts. A calm, sunny spring day can leave the whole basin of the Thames sitting under a shallow layer of trapped air, so a leafy street in Richmond or Dulwich can record much the same PM2.5 as a busy junction in Croydon. Because a large share blows in from outside the M25 — and because tyre wear, brake dust and winter wood burning keep generating it locally — it stays above the World Health Organisation guideline far more often than the headline ULEZ story suggests. If you want to understand why the two pollutants diverge, our explainer on understanding London air quality breaks down the difference between a gas and a particle.

What the yearly trend changes for your flat

The honest takeaway is that outdoor policy works slowly and unevenly, while the air inside your home is something you can change this week. During a still spell, outdoor PM2.5 seeps indoors through trickle vents, letterboxes and the gaps around older sash windows — the kind found across much of London's Victorian and Edwardian housing stock. A high-airflow purifier running quietly overnight keeps the bedroom well below the street reading, which matters most for the eight hours you spend asleep there.

• Check the London borough air-purifier guide for the sizing that suits your room and local pollution level.
• Keep the unit where you sleep; see why in our note on the bedroom air purifier setup.
• For gases as well as particles, the difference between filter grades is covered in MERV-13 versus HEPA.

None of this replaces the slow work of cleaning up London's traffic and heating. But while that continues, sealing and filtering the rooms you actually live in is the part of the problem firmly within your control — and it costs far less than most Londoners expect.