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Calibrating Defra’s Background NOx and NO2 Maps against 2017 Measurements


Air Quality Consultants Ltd has carried out an analysis of the validity of Defra’s national pollution maps of ambient background concentrations in 2017.  These maps cover the whole country on a 1x1 km grid and are published for each year from 2015 until 2030. Mapped concentrations in 2015 were based on existing emissions from a range of different sources (including road traffic) calibrated against monitoring data for that year.  Emission projections are then used to predict concentrations in all subsequent years to 2030.  

Air Quality Consultants Ltd has compared Defra’s background mapped nitrogen oxides (NOx) and nitrogen dioxide (NO2) values for 2017 with national background measurements made at Automatic Urban and Rural Network (AURN) sites during 2017.  Based on the 51 sites with more than 75% data capture for 2017, the Defra maps have been found to under-predict the background NOx and NO2 concentrations by 10.1% and 6.6% on average, respectively (analysis available here).

This analysis also has implications for Air Quality Consultants’ suggested approach to treating background concentrations of nitrogen dioxide (NO2) and nitrogen oxides (NOx) when using the Calculator Using Realistic Emissions for Diesels (CURED) V3A, which was published in 2018 (note available here).


Celebrating 25 Years


Air Quality Consultants (AQC) is celebrating 25 years of providing expert support on air quality matters.  The Company has grown to become the largest, specialist air quality consultancy in the UK, with 29 staff supporting a wide range of public and private sector clients.  Demand has grown considerably, and AQC now completes over 500 air quality projects a year, throughout the UK and internationally, from its offices in Bristol and London. 

Chris Whall joined AQC in January 2016, and took over as Managing Director in January 2018.  He is supported by Stephen Moorcroft, who has been a Director since 2004.  Prof. Duncan Laxen, the founder of AQC, continues to provide support as an Associate.

Chris said “I feel privileged to be leading a company with a 25-year history of providing high quality consultancy to a wide range of clients in the UK and abroad.  I will be focussing on maintaining this quality and continuing our role as leaders in the field”.

The focus of the company is on providing high quality support to clients.  This is enabled by the quality of its staff; the majority of consultants have Masters or PhD qualifications.  With this level of expertise, AQC plays a central role in the development of tools and guidance to support air quality management and assessment.  A major focus in recent years has been on emissions from diesel vehicles, and AQC has developed a tool to improve estimates of current and future year emissions (more here).

AQC has also published a detailed review of trends in concentrations of nitrogen dioxide across the UK (more here). This has shown that while the UK has experienced an overall slow improvement over the last 11 years, this is not the case for all sites.  In particular, no significant trend was found for a large part of the country, covering Central and Northern England. 

There is still clearly much to be done to achieve the improvements that are required to reduce the health burden of air pollution.  In this context, AQC is helping several local authorities develop Clean Air Zones, to meet the Government’s latest requirements.  AQC is also providing policy support to the Greater London Authority, exploring options for implementing an “Air Quality Positive” approach for new developments, and developing guidance for the preparation of Air Quality Assessments.  

AQC continues to work on projects that cover the full range from a small residential block alongside a highly polluted road, to major developments involving several thousand houses.  AQC has also contributed to major infrastructure projects including Thames Tideway Tunnel, Silvertown Tunnel in London, the M4 ‘Smart’ motorway, a new port terminal at Tilbury, expansion at London City Airport and a third runway at Heathrow Airport.   Seven of AQC’s consultants have experience of giving expert evidence at Public Inquiries and DCO Hearings.

AQC has prepared an interactive Timeline which maps key developments in air quality legislation and guidance over the last 25 years, and identifies key milestones in the Company’s history (click here).

NO2 and NOx trends in the UK 2005 to 2016


Air Quality Consultants Ltd has reviewed trends across the UK over an 11-year period.  Results are presented for 156 automatic monitoring sites and show an average downward trend of around 1.5% per year for both nitrogen dioxide (NO2) and nitrogen oxides (NOx).  The downward trends are steeper at rural sites than at urban and road sites.  The report is available here.

While the trend is downward overall, this is not seen at all sites.  Around a third of sites show no significant trend, with around 3% to 4% having an upward trend.  Importantly, no significant average trend in either NO2 or NOx has been found across sites in Central and Northern England and North Wales (the map below shows the NO2 results).  The reason for this is unclear, but may be significant for air quality management in these areas.



Air Quality Consultants has updated its Calculator Using Realistic Emissions for Diesels (CURED) sensitivity test for vehicle emissions to Version 3A (CURED V3A), available here.

The CURED model was originally created in recognition of the disconnection between ‘official’ emissions factors for nitrogen oxides, as published by Defra (in its Emissions Factors Toolkits (EFTs) V6 and V7), and those measured in the real world.  CURED Versions 1A and 2A were produced following a detailed review of real-world emissions factors carried out by Air Quality Consultants.  They worked by calibrating the ‘official’ emissions factors, at that time based on emission functions from COPERT V4.10 and V4.11, against measured data.

Defra recently released a new version of its EFT (V8.0.1), which now uses emissions functions from the COPERT V5 model.  Air Quality Consultants has previously compared the COPERT V5 functions with those contained in the CURED V2A model.  For the current fleet of diesel cars and vans, COPERT V5 agrees closely with CURED V2A.  However, COPERT V5 (and thus EFT V8.0.1) also assumes that those diesel cars and vans manufactured in the future will perform better than those that have currently been tested, which are captured within CURED V2A.

Unlike in the past, where there was evidence showing that EFT V6 and EFT V7 under-predicted emissions from the latest diesel cars and vans, the position for EFT V8 is that its predictions for existing vehicles are a reasonable match to real-world emissions.  The key remaining questions relate to the performance of future vehicles (which are currently untested) and the projections regarding how quickly these vehicles, and other technology types, will populate the fleet.

Air Quality Consultants has reviewed the evidence and considers that there are now reasons to now be optimistic about future NOx emissions.  There are, however, still sources of uncertainty and so it seems prudent to continue to apply a CURED sensitivity test to allow for the possibility that EFT V8.0.1 is over-optimistic. 

CURED V3A follows most of the same assumptions as EFT V8.0.1, but simulates the failure of post-2020 diesel cars and vans to provide any improvement over those that are currently entering the fleet.  The figure below shows how EFT V7.0, EFT V8.0.1, CURED V2A, and CURED V3A predict emissions per vehicle might change over time normalised to a 2016 base year.  More details on the development of CURED V3A are provided here. 


Monitoring and modelling of air quality across Ashdown Forest


Results from a comprehensive monitoring and modelling programme carried out by Air Quality Consultants have been published by Wealden District Council [available here in two parts: Part 1 and Part 2].  They form part of an ongoing study of air quality conditions across the Ashdown Forest Special Area of Conservation. 

The impacts of air quality on the Ashdown Forest have gained national attention since Wealden District Council successfully challenged a neighbouring planning authority’s Local Plan in court for not considering  cross-border impacts on protected habitats in Wealden. 

The 460 page report by Air Quality Consultants presents measurements of a suite of relevant pollutants made over a number of years, along with the results of detailed dispersion and deposition modelling.  The study will be used to inform the Habitats Regulations Assessment of the Local Plan being prepared by Wealden District Council.

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