London vs Southampton: PM2.5 compared

Over the last year, London's air was 18% more polluted than Southampton's: PM2.5 averaged 9.7 µg/m³ against 8.2, on the 150 days both cities were measured. London had the dirtier air on 109 of those days, Southampton on 40. London was over the WHO's daily guideline of 15 µg/m³ on 16 of them, Southampton on 12.

Right now

London#546on the 24-hour board of 738, at 18 US AQI (3.3 µg/m³)

Southampton#613on the 24-hour board of 738, at 16 US AQI (2.8 µg/m³)

The last year, day by day

London

Southampton

Each city's daily mean from 8 Oct 2025 to 7 Oct 2026, one stripe a day, coloured by band. A blank stripe is a day without a daily mean.

Month by month

Monthly means in µg/m³ over the days both cities were measured. Solid: London. Faded: Southampton. A month shows once both share 10 such days. Dashed line: the WHO daily guideline, 15 µg/m³.

Year by year

Year	London	Southampton	Days both measured	Days London was worse
2026 so far	54	49	92	67
2025	49	41	238	182
2024	46	37	259	190
2023	49	47	221	136

Means in US AQI over the days both cities were measured that year; a year shows once they share 30 such days.

Each city's worst days

London

26 Jan 202610838.5 µg/m³
4 Mar 20269532.5 µg/m³
9 Mar 20269231.2 µg/m³

Southampton

9 Mar 202612143.7 µg/m³
5 Mar 20268226.0 µg/m³
24 Mar 20268226.0 µg/m³

Daily means in US AQI, with µg/m³ beside them, since the index stops at its top value, over the days both cities were measured in the last year. Each date opens that day's world board.

Compare either city with another

London

Side by side with Borehamwood (the nearest), Birmingham (United Kingdom's 2nd worst on 30 days), Gujranwala (the world's worst on 30 days).

Southampton

Side by side with Portsmouth (the nearest), Gujranwala (the world's worst on 30 days).

Use this page

SmogRank, PM2.5 daily means compared, London and Southampton, 8 Oct 2025 – 7 Oct 2026, smogrank.com/compare/gb-london/gb-southampton (accessed 8 Oct 2026).

You're welcome to reuse a single chart, image or figure with this citation and a link. Terms. Raw monitor readings in bulk are published by OpenAQ, under each provider's licence.

The same rules as every SmogRank figure: reference monitors first, and a day counts with 18 measured hours. How we measure.

Updated 2026-10-08 20:07 UTC. Values are PM2.5 (fine particles), the median of each city's monitors, as the US AQI PM2.5 sub-index. Some readings: Uzhydromet (Uzbekistan's Hydrometeorological Service); Department of Environment, Nepal; Vietnam's government monitors; Aurassure; Umhverfisstofnun (Environment Agency of Iceland); Love My Air (City and County of Denver), no reuse terms published (why we use them).