Air quality and how Portsmouth moves
Nitrogen dioxide has more than halved since 2001 and bus use has fully recovered past pre-pandemic levels — but two streets still breach the legal limit, and the Clean Air Zone cannot be credited for the improvement.
The Clean Air Zone generated significant debate at launch. Air quality itself is raised less often than sewage or fly-tipping despite affecting far more people.
Air pollution affects the whole population continuously. OHID attributes roughly 4.9% of Portsmouth adult mortality to particulate pollution — down from 9.1% in 2018, but still substantial.
NO2 at the urban background monitor fell from 27 µg/m³ in 2001 to 12 in 2025, and at the roadside monitor from 31 in 2018 to 19. Portsmouth moved from three streets in breach at the 2023 assessment to none at the 2026 assessment. Bus journeys per head have returned above their pre-pandemic level while England's have not.
Who pays in the Clean Air Zone?
Portsmouth runs a Class B zone. Private cars, vans, motorcycles and minibuses are not charged at all.
- Private cars£0
- Vans (LGVs)£0
- Motorcycles£0
- Minibuses£0
- Taxis & private hire£10/day
- HGVs£50/day
- Buses & coaches£50/day
Compliant means Euro 6 diesel or Euro 4 petrol. Just under 94% of vehicles entering the zone in its first two years were already compliant or exempt. Under 1% were chargeable.
Limitations of this diagram
Charge classes are defined by the national Clean Air Zone Framework. No claim is made here about how any revenue is applied: the legal basis for ring-fencing has not been verified from a primary source, so it is not asserted either way. Diesel cars account for 58–59% of road NOx at those sites, and diesel vans another 18–20% — neither is charged by a Class B zone. Cars registered in Portsmouth rose 17% between 2011 and 2021 against 5% nationally.
NO2 has more than halved since 2001
Nitrogen dioxide at Portsmouth's urban background monitor has fallen from 27 µg/m³ in 2001 to 12 in 2025, and at the Anglesea Road roadside monitor from 31 in 2018 to 19. The hourly objective of 200 µg/m³ has never been breached at either site in any year on record.
The background monitor's 2020 and 2021 readings are omitted: data capture was 15% and 65%, below the 75% threshold at which a year counts as valid. Plotting them would show a dip that is an artefact of the monitor, not the air.
The two streets that were in breach
Bias-corrected annual mean from diffusion tubes, against a 40 µg/m³ limit. Sites above 40 fell from four in 2022 to three in 2023 to one in 2024. The council states that after bias, distance and siting adjustments the objective was not exceeded at any location in 2024. Diffusion tubes and the continuous analysers are different instruments and are not interchangeable — the one remaining 2024 reading above 40 is a tube result the council says meets the 2010 Regulations but not local monitoring siting standards.
The zone is still operating. Portsmouth passed the State 2 Assessment in January 2026 with zero exceedances, having failed State 1 in November 2023 with three. If it also passes States 3 and 4, the council plans to decommission the zone in 2027 at the earliest. The five Air Quality Management Areas declared in 2005 remain in force — none has been revoked following compliance.
Failed in 2023, passed in 2026
Government assesses compliance in stages. Portsmouth failed the first with three streets in breach, and passed the second with none.
- 1State 1 Assessment · November 2023
Failed — not on track for compliance
3 exceeding · 9 at risk
- 2Targeted Feasibility Study · December 2024
No change to boundary or charges; rely on fleet renewal
- 3Government response · March 2025
Accepted no further measures would speed compliance; rejected a £2m behaviour-change package as poor value
- 4State 2 Assessment · January 2026
Passed — no exceedances at any of 12 assessed locations
0 exceeding · 3 at risk
- 5State 3 & 4 · End 2026 (planned)
Modelling and exit plan
- 6Decommissioning · 2027 at the earliest
Conditional on passing States 3 and 4
Why the improvement cannot be credited to the CAZ
No official evaluation attributes any NO2 reduction to the Clean Air Zone, and the council's own commissioned study points the other way. It records that "monthly traffic volumes on Alfred Road are largely higher than when the CAZ was first introduced in 2021, suggesting that traffic levels have not decreased since the CAZ became operational", and that there is "limited scope for further NO2 benefits as a result of further vehicles being upgraded". The largest single fall at the roadside monitor was 2019 to 2020 — COVID, a year before the zone opened.
Why a Class B zone cannot fix it: Diesel cars account for 58–59% of road NOx at those sites, and diesel vans another 18–20% — neither is charged by a Class B zone. Cars registered in Portsmouth rose 17% between 2011 and 2021 against 5% nationally.
Non-compliant taxis and private hire £10/day; non-compliant HGVs, buses and coaches £50/day. Private cars, vans and motorcycles are NOT charged. Compliance standard: Euro 6 diesel / Euro 4 petrol.
Air Quality Management Areas
All 13 were declared on the same day in 2005 for nitrogen dioxide, all attributed to local authority roads. Eight were revoked in 2010; five remain in force. The five still in force are: Fratton Road to London Road; Central Portsmouth — High Street, St Georges Road, Cambridge Road and surrounding; Milton Road to Eastern Road, Milton; Marketway to Lake Road to the M275; The Hard to Queen Street, Portsea.
Fully recovered — and ahead of where it was
Portsmouth bus journeys have not just recovered from the pandemic — they now exceed pre-pandemic levels. 11.9 million journeys in the year to March 2025 against 11.0 million in 2019. Across England, patronage remains around 10% below where it was.
Financial years ending 31 March. England journeys per head have fallen steadily since 2010 and remain well below their pre-pandemic level; Portsmouth's have not. Figures from 2022 onward are provisional.
Walks and cycles far more than England
Portsmouth walks and cycles to work at well above the national rate — 12.7% on foot against 7.6%, and 5.2% by bicycle against 2.1%. Nearly a third of households have no car at all, against under a quarter across England. Density and a compact island geography make active travel genuinely viable here in a way it is not in most of the country.
Method of travel to work
Households with no car
Nearly a third of Portsmouth households have no car. On an island with the second-highest population density of any local authority outside London, walking and cycling are genuinely practical for a large share of journeys.
Census 2021 was taken during the pandemic, which affected travel-to-work answers substantially — most obviously the home-working figure. ONS states this explicitly. The comparison with England is still valid because both were measured the same way at the same moment.
Flat since 2004 — but vans keep growing
Total traffic in Portsmouth peaked in 2004 and has been broadly flat since. Car traffic in 2025 is close to where it was two decades ago. The growth has been in vans: light goods traffic is up about 69% since 1993, while heavy goods traffic has fallen around 22%.
DfT states that local-authority traffic estimates are not accredited official statistics and are less robust than regional and national totals. Motorcycles, buses and cycles are not published at this geography.
Where the council's air quality reporting lives — and where it stops
Portsmouth City Council does not publish its Air Quality Annual Status Reports on its own website — its air quality page lists more than twenty other documents but no ASR, and directs residents to email for a copy. Four full reports are nonetheless public, as committee appendices or through a planning examination.
| Report | Data year | Where it is public |
|---|---|---|
| 2016 ASR | 2016 | Committee appendix |
| 2018 ASR | 2017 | Committee appendix |
| 2019 ASR | 2018 | Committee appendix |
| 2020 ASR | 2019 | Submitted to the AQUIND planning examination — never attached to a council agenda |
For 2020, 2022, 2023 and 2024 data, only a short covering report to committee is public. The full reports run to 400+ pages and are not published.
One year is simply missing. The 2022 report, covering 2021 data, does not exist. A council report of January 2023 states plainly: "The 2021 ASR was submitted to DEFRA in line with these responsibilities, however, the 2022 ASR has not been submitted." There is also no 2017 report — the sequence runs 2016 then 2018 — and nothing has been published for 2025 data.
Portsmouth City Council, under government direction
States 3 and 4 of the compliance assessment, end 2026
Respond to the Clean Air Strategy consultation; the council publishes air quality reports on request
The Clean Air Zone remains a live local argument, and air quality connects directly to the health outcomes covered separately.
Public and political discussion indicates what people are raising. It is not evidence that a claim is true.
Verified facts
Full detail — why it matters, who else is involved, what is being done
- •Portsmouth City Council — Operates the Clean Air Zone, declares Air Quality Management Areas, sets local transport policy
- •UK Government (Defra / JAQU) — Sets limit values and issued the Ministerial Direction requiring the zone
- •Vehicle owners and fleet operators — Fleet turnover is what actually drives most of the reduction
- •Bus operators — Commercial services account for the great majority of bus mileage
- •Portsmouth City Council does not publish its Air Quality Annual Status Reports on its own site. Four full reports are public via committee papers or a planning examination (2016, 2018, 2019 and 2020 editions); for the other years only a short covering report exists, and the full documents run past 400 pages. The 2011–2024 diffusion-tube trend across 27 sites exists only as a chart image.
- •One year is simply missing: the 2022 report, covering 2021 data, was never submitted to Defra — the council states this itself. Nothing has been published for 2025 data.
- •The background monitor's 2020 and 2021 readings fall below the 75% data-capture threshold and are omitted rather than plotted.
- •PM10 measurement methods changed twice over the series, so it is not one continuously comparable record.
- •DfT states that local-authority traffic estimates are not accredited official statistics.
- •The latest walking and cycling survey data for Portsmouth covers only to November 2023.
- •One continuous-analyser reading (37.70 µg/m³ at Alfred Road) is published by the council as both its 2023 and its 2024 value in two different committee reports. The conflict is unresolved and the underlying Annual Status Reports are not published.
Sources & methodology (3) · last verified 2026-08-26
What could be done, and what it would cost
Full action plan →UK Stat Pack's own analysis — not Portsmouth City Council or government policy. Each item states what is officially happening, if anything.
Complete a signposted cycle circuit of Portsea Island
Not proposed officiallyWhy it might work, and the trade-offs
Most of the individual segments already exist or are being built as part of other funded schemes (Hilsea Lines restoration, Southsea Coastal Scheme) — the missing piece is junction treatment and continuity, not building a route from scratch.
Trade-offs. Junction redesigns that favour cyclists can reduce motor-vehicle capacity at pinch points on an island with only one main road in and out — a real trade-off given Portsmouth's existing traffic congestion.
How we would know it worked. Number of dangerous junctions resolved; Cycle trip counts on the connected route