Hounslow / Planning, sources and design
Air quality assessment in Hounslow
Prepare your Hounslow air quality assessment around local roads, relevant sources and the people using the site. ACP supports planning evidence, monitoring and mitigation from initial scope to a coordinated submission.
Connect current local policy, the latest monitoring and practical design decisions.
Discuss your projectPolicy and validation
EQ4, the council-listed SPD and the right application checklist.
Representative local evidence
Roadside and background stations, diffusion tubes and qualified particle data.
Coordinated design
Occupied façades, transport, plant and construction considered together.
01 / Local context
From the Great West Road to Heathrow-side neighbourhoods
Hounslow’s air-quality setting changes between Heathrow-side neighbourhoods, the Great West Road corridor, town centres and residential streets. Local Plan Policy EQ4 identifies traffic as a major source and links development emissions with the exposure of future occupants. Select evidence for the actual road, height and use.
Brentford and the Great West Road
Coordinate traffic, servicing and energy sources with new homes and occupied façades. The roadside Brentford station provides a useful history, but its position does not represent every building or intake.
Chiswick and Gunnersbury
Street geometry, busy roads and proposed façade changes can affect exposure. Compare representative roadside observations with the site layout and assessment year rather than transferring a station result directly.
Heston, Feltham and Heathrow-side settings
Separate road, airport-related and background contributions where relevant. Explain what each dataset includes, the role of local plant and whether additional monitoring would resolve a specific evidence gap.
Construction and mixed uses
Plan demolition, trackout and plant controls alongside occupied neighbours. Where extract, odour or fan noise matters, use a coordinated brief with consistent drawings and operating assumptions.
Whole-borough AQMA: Defra records Hounslow’s borough-wide designation from 7 March 2006 for annual NO₂. The designation does not mean every current monitor exceeds the objective, nor does a lower borough average settle the exposure at a proposed façade.
02 / Monitoring and trends
Read the newest results in their local setting
The latest linked report was published on 30 September 2026 and covers 2025 measurements. Chiswick’s annual NO₂ fell from 28 to 24 µg/m³; Gunnersbury rose from 28 to 29.9 µg/m³. Both were lower than in 2019. These observations describe the sites and do not isolate the effect of a particular project or intervention.
Annual NO₂ / 2019–2025
Lower than 2019, with different recent directions
Annual objective: 40 µg/m³
Chiswick
HS4 · roadside automatic
24.0µg/m³2025 annual mean
Gunnersbury
HS8 · roadside automatic
29.9µg/m³2025 annual mean
Shared 0–60 µg/m³ scale · reported annual measurements at each monitoring location.
Read the annual values
| Year | Chiswick HS4 | Gunnersbury HS8 |
|---|---|---|
| 2019 | 41.7 | 45 |
| 2020 | 32 | 37 |
| 2021 | 32.9 | 35.9 |
| 2022 | 31 | 29 |
| 2023 | 29 | 31 |
| 2024 | 28 | 28 |
| 2025 | 24 | 29.9 |
2025 NO₂ capture was 95.0% at Chiswick and 98.5% at Gunnersbury. All six automatic annual NO₂ means in Table D were below 40 µg/m³. That does not demonstrate conditions at every relevant receptor. Read the full report and method notes.
03 / Network and interpretation
Six stations, diffusion tubes and particle data gaps
Six automatic monitoring sites
The report lists Chiswick, Brentford, Heston, Hatton Cross, Gunnersbury and Feltham, with NO₂, PM₁₀ and PM₂.₅ channels. Hatton Cross is classed as urban background; the other five are roadside. Each pollutant has its own capture record.
56 diffusion-tube locations
Table C lists 66 individual NO₂ tubes at 56 distinct locations, counting co-located triplicates as one location. These cover roadside and background settings and help check automatic-monitor bias. Tubes do not measure particles, odour or short-term NO₂ peaks.
| 2025 site | PM₁₀ / capture | PM₂.₅ / capture |
|---|---|---|
| Chiswick | 15.8 / 70.3% | 9.8 / 77.0% |
| Brentford | 18.5 / 79.3% | 8.8 / 67.2% |
| Heston | 18.1 / 58.4% | 10.5 / 56.0% |
| Hatton Cross | 15.4 / 61.9% | 9.4 / 60.9% |
| Gunnersbury | 18.9 / 36.3% | 9.9 / 36.3% |
| Feltham | 15.7 / 40.2% | 9.8 / 51.1% |
Read the particle figures with their limitations. Several channels had equipment-related gaps. The report annualises results where capture is below 75% and above 25%, using comparator stations. A lower reported mean is not, by itself, evidence of a reliable year-on-year improvement. Earlier zero entries for newly reported PM₂.₅ channels are not treated here as measured zero concentrations.
Use Defra local-authority data alongside council observations and appropriate background inputs. Check measurement year, siting, capture, bias adjustment and local source coverage before combining datasets.
04 / Planning requirements
Connect EQ4, local guidance and validation
EQ4: impacts and exposure
Adopted Policy EQ4(d) expects AQA for major developments and changes of use to air-quality-sensitive uses. Read its impact and exposure requirements with EQ4(c) on Neutral development and EQ4(e) on mitigation. Read EQ4, pages 200–201.
Air Quality SPD: local scope
The council lists the Air Quality SPD as 2008. Its cover is dated March 2008, while some internal headers retain June 2007. It addresses new exposure, traffic and combustion sources, construction, street canyons and other material situations. Its historic technical and legislative references need current editions. Council-listed SPD.
Validation: select the application route
The full major/minor checklist, page 9, includes an Air Quality Statement and asks for evidence of exposure and mitigation. It still cites a draft 2013 SPD and an older action plan in supporting entries. Read it with EQ4, the currently listed adopted SPD and current guidance. Choose the relevant checklist.
Design and climate guidance
Coordinate EQ4 with the 2024 Character, Sustainability and Design Codes SPD and the 2025 Climate Change Mitigation and Adaptation SPD. Align layout, façade treatment, energy and ventilation assumptions. These design references do not replace a representative exposure assessment.
The London air-quality guide connects local assessment with current London Plan and GLA Neutral or applicable Positive requirements. Keep the local impact assessment and benchmark calculations identifiable within the submission.
05 / Local assessment briefs
Four Hounslow settings. Four different briefs.
These illustrative briefs show how local evidence can inform a proposal’s layout, assessment and mitigation.
Brentford: homes beside the Great West Road
For a mixed-use frontage, map occupied floors, balconies and air intakes before fixing the façade design. Compare the roadside Brentford evidence with the proposed setback and height; combine traffic and energy inputs without counting background contributions twice.
Useful outputA receptor plan and a comparison of layout and intake options, with assumptions shared by the transport and ventilation teams.
Chiswick: a new sensitive use on a busy frontage
For a conversion near Chiswick High Road or Gunnersbury, test whether the existing evidence represents the new rooms and operating pattern. The two automatic stations have different recent trends; neither result can simply be assigned to a proposed window.
Useful outputA proportionate EQ4 assessment brief linking monitoring selection, façade exposure and any ventilation or noise constraints.
Heston and Hatton Cross: selecting a baseline
For a Heathrow-side proposal, distinguish relevant roads, airport-related activity, local plant and background contributions. Hatton Cross is an urban-background station and Heston is roadside. Check the source coverage and particle capture before deciding whether targeted monitoring would resolve an evidence gap.
Useful outputA source-and-data schedule explaining what is represented, what remains uncertain and which additional measurements would help.
Feltham: construction beside occupied neighbours
For phased redevelopment, align demolition, earthworks, construction access and first occupation. Identify nearby homes and other sensitive uses in each phase. Where commercial extract or plant is proposed, coordinate odour and fan-noise assumptions with the same drawings and programme.
Useful outputA phased receptor and dust-control plan, with clear responsibilities, review points and proportionate monitoring.
Make the local guidance usable
The council-listed Air Quality SPD separates site suitability from the development’s own effects in section 3.3. Its sections 3.12–3.13 ask for a clear reporting trail, while Appendix 3 sets out information to agree before assessment. Use that structure to organise inputs and decisions, alongside current technical methods.
Connect the brief with air quality assessment, noise and odour when the proposal needs combined evidence. Consider ecological pathways where a relevant source could affect a designated habitat.
06 / Interactive project checklist
Hounslow evidence planner
Answer five questions to organise the assessment brief. Choose “Not sure yet” where information is missing; those points remain visible in your results.
Answers stay in this page. The planner organises evidence; it does not certify compliance or decide planning requirements.
07 / Current changes
Separate adopted policy from the examination
The council’s Air Quality Action Plan 2023–2028 was approved by Cabinet in December 2023. Use it to understand improvement priorities, while reading the newest annual monitoring evidence separately. Current action plan.
The replacement Local Plan 2020–2041 remains in examination. The council’s 8 October 2026 update invites comments on specified post-hearing documents until 5pm on 29 October 2026. For EX82a, the invitation is limited to highlighted changes. The update confirms that examination conformity continues to be assessed against the adopted London Plan 2021. Keep emerging proposals separate from the adopted 2015 EQ4 policy and verify status at the submission date. Current examination update.
Continue to track updated local evidence, London guidance, Defra methods and IAQM guidance. For Heathrow-side or major-road schemes, explain any relevant particle, source-attribution or monitoring gaps rather than inferring unmeasured pollutants from NO₂ or PM mass.
Common questions / Local answers
Hounslow air-quality FAQs
Is the whole of Hounslow within an AQMA?
Yes. Defra records the whole-borough AQMA from 7 March 2006 for annual NO2. This designation is separate from whether a particular current monitor exceeds the objective. Check the actual site and relevant exposure.
Which local policy requires an air-quality assessment?
Adopted Local Plan Policy EQ4 addresses development impacts, sensitive uses, exposure and mitigation. It expects assessment for major developments and changes of use to air-quality-sensitive uses. Read it with current validation and London requirements.
Does Hounslow have an air-quality SPD?
The current adopted-SPD library lists the Air Quality SPD as 2008. Its cover is dated March 2008, while some internal headers retain June 2007. The application checklist also cites a draft 2013 version. Use the council-listed document with current policy and technical methods, rather than assuming the cited draft is adopted.
What is the latest monitoring year?
The latest linked annual report was published on 30 September 2026 and covers 2025 measurements. Annual NO2 was 24 µg/m³ at Chiswick and 29.9 µg/m³ at Gunnersbury, with capture of 95.0% and 98.5% respectively.
Does the borough use diffusion tubes?
Yes. Table C of the 2025 monitoring report lists 66 individual NO2 tubes at 56 distinct locations, counting co-located triplicates as one location. Diffusion tubes measure longer-term NO2, not particles or odour.
Do the particle results show a clear improvement?
Several 2025 particle channels had equipment-related gaps and annualised results. Interpret the reported means with their capture and method notes. A lower mean alone does not demonstrate a reliable year-on-year improvement.
Does every proposal need an airport model?
The scope depends on relevant sources, receptor locations and the assessment question. Identify road, airport-related, plant and background contributions where material. Explain what background data already include and avoid double counting.
Can a previous assessment be updated?
Review its policy editions, monitoring and background inputs, traffic, plant, receptor positions and assessment year against the current scheme. Keep representative evidence and revise material changes, scenarios and mitigation assumptions.
Hounslow / Your next step
Discuss your air quality project
Tell us what you are proposing and where you are in the planning process.
What to include
- Site and proposal. Address or postcode, proposed use and approximate number of homes or floorspace.
- Planning stage. Application reference, any Hounslow Council request or condition, and your target date.
- Local setting. Road exposure, occupied rooms, ventilation, energy plant and construction phases.
- Existing information. Mention available drawings, previous air quality reports and traffic or plant details.
Start with what you have. You can email drawings or council correspondence using the address below.
Your details are handled under our privacy policy.
Evidence / reviewed 23 October 2026
Hounslow guidance and sources
Council policy, validation, report-library and examination sources rechecked 23 October 2026. Monitoring figures retain the detailed 21 October review; the NO₂ and PM₂.₅ tables were also rechecked in the current report text. Measurement and publication years are stated beside the results. Check current documents when preparing a submission.
- Council monitoring report library
- 2025 monitoring: annual report published 30 September 2026
- Adopted Local Plan: EQ4, pages 200–201
- Current adopted SPD library
- Council-listed Air Quality SPD
- Full planning major/minor validation checklist
- Application-type checklist library
- Defra whole-borough NO₂ AQMA
- Air Quality Action Plan 2023–2028
- Character and design codes SPD 2024
- Climate change SPD 2025
- Local Plan examination and October 2026 update
- Defra borough dashboard