SmogRank / Portsmouth / Southampton
Portsmouth vs Southampton: PM2.5 compared
Over the last year, Southampton's air was 12% more polluted than Portsmouth's: PM2.5 averaged 8.4 µg/m³ against 7.5, on the 139 days both cities were measured. Southampton had the dirtier air on 107 of those days, Portsmouth on 29. Southampton was over the WHO's daily guideline of 15 µg/m³ on 12 of them, Portsmouth on 9.
Right now
The last year, day by day
Month by month
Year by year
| Year | Portsmouth | Southampton | Days Portsmouth was worse |
|---|---|---|---|
| 2026 so far | 45 | 49 | 23 |
| 2025 | 39 | 42 | 44 |
| 2024 | 41 | 38 | 168 |
| 2023 | 48 | 47 | 133 |
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
Portsmouth
- 9 Mar 202610637.4 µg/m³
- 24 Mar 20267823.4 µg/m³
- 20 Mar 20267421.4 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
Portsmouth
Side by side with London (United Kingdom's worst on 30 days), Gujranwala (the world's worst on 30 days).
Southampton
Side by side with London (United Kingdom's worst on 30 days), Gujranwala (the world's worst on 30 days).
Use this page
SmogRank, PM2.5 daily means compared, Portsmouth and Southampton, 8 Oct 2025 – 7 Oct 2026, smogrank.com/compare/gb-portsmouth/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).