Published: Friday, 26 June 2020

The City Council has published an assessment of the sources of air pollutants across the city, examining NOX, PM2.5 and PM10.

The data, which was gathered in December 2019, was compiled by independent experts, Ricardo Energy and Environment, explores which sectors (transport, domestic heating, industry heating, and other sources) contributed towards these emissions across Oxford.

The data will help inform the City Council’s new Air Quality Action Plan (AQAP) which will be published later this year, and will outline the air quality targets and measures to be achieved between 2021-2025. 

Last year the City Council published data on total carbon emissions across the city, this December 2019 data from Ricardo highlights the source of pollutants in the city such as nitrogen oxides, PM2.5 and PM10 which can all have direct impacts on public health.

The city of Oxford is compliant with legal limits as well as WHO advisory limits for PM10 and PM 2.5, and is currently working to reduce harmful NOx emissions, such as Nitrogen Dioxide (NO2) - which is currently breaching the annual mean legal limit in some areas of the city.

The report

Key highlights

In December 2019 Oxford City Council commissioned Ricardo Energy & Environment to carry out a new source apportionment study in order to obtain information in four key areas:

  • Identifying the sectors which contribute towards NOX, PM2.5 and PM10 emissions in Oxford
  • Identifying which vehicle types have the greatest contribution towards air pollutants emissions across Oxford
  • Identifying the reduction in road NOX emissions needed to reach air quality target and determine the scale of further work that is required (focusing on St Clements, George Street, High Street and Cutteslowe roundabout where annual mean air pollution limits were exceeded in 2018)
  • Understanding the impact of the City and County Council plans to introduce a new Low Emission Zone for buses to be a minimum of Euro VI standard as part of the Oxford Zero Emission Zone proposals

The report found that in Oxford:

  • The transport sector contributes 68% of NOX emissions
  • Domestic combustion (primarily used for domestic heating) accounts for 19% of NOX emissions
  • Industry and service combustion accounts for 12% of NOx emissions
  • Nature, waste, solvents, and agriculture accounts for just 0.26% of NOX emissions


The report found that the transport sector is the largest contributor of NOX emissions in the city, accounting for 68% emissions – diesel cars and buses contributes 33% and 32% respectively to NOX emissions.

The study also reveals that transport contributes to 18% of PM10 and 21% PM2.5 emissions across the city - with cars contributing to 48% of PM10 and 43% of PM2.5 transport emissions.

At St Clement’s Street /The Plain a reduction of 16.9% of road NOx emissions is required in order to achieve compliance with the annual mean. At George Street, High Street and Cutteslowe, the required reductions of road NOX are of 9.5%, 22.9% and 4.2%.

According to the modelling on St Clement’s, after the conversion of all buses to Euro VI, NOx emissions from buses are estimated to decrease from 69.9% to 29.3% - a decrease of 40.6%. This shift would mean that one of Oxford’s worst streets for air pollution levels, would achieve legal compliance – with modelled NO2 concentration falling from 48.0 μg/m3 to 30.8 μg/m3 for the street (a reduction of 17.2 μg/m3 or 36%).

Similarly, at Worcester Street and Botley Road, the introduction of EuroVI buses would see reductions of 15% and 26% NOx respectively were predicted.

It is expected there would be further reductions once Oxford’s fleet becomes fully electric by 2035 at the latest.

Comparison with 2013 data

When compared with the last study of this kind, conducted in 2013, the data shows a 7% decrease in NOX emissions for transport (from 75% to 68%).

Since 2013 NOX emissions from buses contribution to transport emissions have decreased by half (64% to 32%), this is largely due to the introduction of Euro VI standard buses into Oxford over the last few years as well as the retrofitting of buses to Euro VI standard through the Clean Bus Technology Fund awarded to Oxford City Council.

NOX emissions from cars have increased by 22% - from 15% to 37% of transport emissions. However, this increase is largely due to the reductions observed in bus emissions during the same period, as well as the update in emissions data which now reflect the impact of real world car emissions.

Domestic heating

The report found that domestic combustion (which is primarily used for domestic heating) accounts for 19% of NOX, 48% of PM10 and 66% PM2.5 emissions in Oxford.

Industry heating/production

The report found that industry and service combustion (heating) accounts for 12% of NOx emissions, 26% of PM10 and 4% PM2.5 emissions in Oxford.

Other sources

Other sources such as nature, waste, solvents, and agriculture accounts for 0.26% of NOx, 7% of PM10, and 9% of PM2.5 emissions in Oxford.

Tackling Oxford’s air pollution

The City Council, working with its partners remains committed to tackling air pollution across the city through the Oxford Zero Emission Zone and Connecting Oxford proposals.

In March, the City Council and County Council announced that the launch of the zone would be postponed for six months from late 2020 until summer 2021 as a result of the pandemic.

The Government has suspended all Clean Air Zones, including in Birmingham, Leeds and Bath, until at least January 2021 due to the impact of the pandemic. Oxford was introducing a Zero Emission Zone voluntarily, rather than at the instigation of Government, and requiring higher emissions standards than the Clean Air Zones.

This delay was in recognition that businesses and residents across the city, and particular in the Red Zone, need to focus their attention on managing the current and potential impacts on their trade and way of life during the coronavirus pandemic.

“Oxford is breathing cleaner air, perhaps the cleanest ever. Our clean air measures have led to a big reduction in harmful emissions from transport in recent years, but the council has more to do to ensure everyone is breathing the very cleanest air.

“Oxford’s Low Emission Zone has significantly reduced emissions from buses and our Zero Emission Zone will be the real game-changer to ensure citizens are not choking on toxic air. In particular, the operation of cleaner buses will ensure that air quality on St Clement’s Street becomes legally compliant with very significant reductions. The council will continue to encourage people and businesses to switch from older polluting vehicles into cleaner ways of getting around including public transport, cycling and walking.”

Councillor Tom Hayes, Deputy Leader and Cabinet Member for Green Transport and Zero Carbon Oxford

“We continue to be fully supportive of Oxford City Council’s measures to improve air quality in the city and will further invest in our fleet of vehicles to reduce emissions and improve air quality. Investment in our vehicles will also work to make the bus a more attractive option to encourage car users to consider greener public transport. All of our vehicles are fitted with eco-driving technology to help deliver fuel efficiency and reduced CO2 emissions and we continue to look at new ways we can improve on this.

“It is very encouraging to see the contribution by Oxford's buses to the overall transport emissions is down from 64% to 32%, this is extremely positive and a promising improvement. We will continue to work with the local authorities to lowering this percentage.

"Covid-19 has given us a window on what could be a positive future world - one with dramatically fewer cars on our roads, safer streets, cleaner air and less damage to our environment. Buses will continue to play a crucial role in supporting the renewal of cities like Oxford as we look to emerge from the pandemic."

Chris Coleman, Managing Director of Stagecoach Oxfordshire

“We welcome the significant reduction in NOx emissions from buses in Oxford, which has greatly contributed to improving air quality in the city.  

“This is due to our major and on-going investment in Euro VI vehicles, as part of our values to be socially responsible. 

“We are committed to reducing NOx emissions further. More than half our buses are now powered by hybrid technology and earlier this year we introduced our first electric bus into service. We have also submitted a bid to the DfT Bus Town fund, to seek funding to start electrifying our city fleet in 2022.”

Phil Southall, Oxford Bus Company Managing Director

The full report is available to download and read.

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