Air pollution in Oxford increased for the first time in years during 2019 due to extreme weather

Published: Monday, 6th July 2020

Extreme weather conditions experienced throughout three months of 2019 have resulted in an increase in air pollution levels across the city.

This increase is masking data which would have otherwise shown a continuation of the plateauing trend which has been taking place over the past few years.

The first significant increase in air pollution levels since 2011 masks a plateauing trend which illustrates that more needs to be done to tackle pollution in the city, including the introduction of a Zero Emission Zone to restrict polluting vehicles.

New data from Oxford City Council’s 71 air pollution monitoring locations has shown that levels of toxic nitrogen dioxide (NO2) increased by an average of 7.9% (roughly 2-3 µg/m3)  between 2018 and 2019 – the first significant overall increase on average since 2011, which saw a 6.9% yearly increase.

However, this increase can be explained by extreme episodes of cold and still weather that occurred throughout the months of February, April and November.

Across the 64 sites where NO2 was monitored in both 2018 and 2019, 70% of sites showed increases of air quality levels; 16% measured the same levels as the previous year and 9% showed slight decreases in NO2 values.

The increase has largely been attributed to extreme weather conditions rather than increases due to traffic/congestion. Evidence to support this includes: traffic data for 2019 did not show any significant increases in traffic levels in Oxford city when compared with 2018 data, significant rises in NO2 is consistent with meteorological data for extreme weather, and increases in NO2 are observed across the city, not just in particular locations.

However, despite this increase, only six sites out of the 71 sites that were monitored in 2019 were in breach of the annual legal limit (High Street, Long Wall Street, St Clements (on two monitoring stations), George Street, St Aldate's).

The European Union requires national governments to keep annual average NO2 levels in towns and cities across their countries to below 40µg/m3 – a legal limit that was supposed to be met in 2010. However, there is no safe limit for NO2.

In response to the UK leaving the EU, the UK Government introduced a new Environmental Bill to parliament in October 2019. Along with the commitment to set targets on air quality for the UK, the new Bill also promises the creation of a new independent Office for Environmental Protection to scrutinise environmental policy and law, investigate complaints and take enforcement action against public authorities, and if necessary, to uphold current and future environmental standards.

Over the past decade NO2 levels in Oxford have decrease by 29%, this is mainly due to the introduction of a Low Emission Zone (LEZ) for buses in the city in 2014 and £2.3m Government funding to the retrofit of several buses to cleaner Euro VI engines.  Oxford has also submitted a bid to become Britain’s first all-electric bus city through the Government’s All-Electric Bus Town fund.

According to Oxford’s most recent Source Apportionment Study, the transport sector is by far the most significant source of emissions of NO2 in the city, accounting for about 68% of emissions. According to the modelling of the Source Apportionment Study, after the conversion of all buses to Euro VI, NOx emissions from buses at St Clement’s 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 48.0μg/m3 to 30.8μg/m3 for the street (a reduction of 17.2μg/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.

The City and County Councils are working together on the Oxford Zero Emission Zone and Connecting Oxford proposals, which aim to reduce traffic, improve air pollution, and improve health across the city.

Impact of colder weather

During January/February, April, and November, the city saw record-breaking temperatures of cold weather, occurring during high pressure systems. A high pressure system provides stable atmospheric conditions in which dispersion of pollutants is poor, and are often precursors to air pollution episodes. This resulted in increases of NO2 levels during those months, with NO2 levels in all other months remaining consistent with previous years.

The impact of cold weather has resulted in an overall increase of the annual mean NO2 by 2-3μg/m3.

However, if the rise in NO2 due to weather was not accounted for, air pollution levels would have continued to shown the plateauing trend that has been observed since 2017.

The plateauing trend observed means that we continue to need a rapid change in fleet make up to ensure as much of it as possible is electric and to tackle levels of congestion; the proposed Zero Emission Zone and Connecting Oxford proposals are predicted to do this. 

The overall increase in air pollution levels shows that there needs to be continued action to reduce emissions across the city to ensure that air quality levels reduce significantly, and ensure that Oxford’s air is not just cleaner, but safer to breathe.

“Unlike the smog from industrial chimneys and cigarette smoke, you can't see the air pollution caused by fossil fuel vehicles. However, we can see the evidence of its impact in the ill health of residents exposed to polluted air. We’ve made progress in our efforts to achieve better air quality and a high quality of life, but we need to bring in cleaner buses, reduce the numbers of fossil fuel vehicles on our roads, and create segregated cycle routes. That way we can truly achieve the cleanest possible air for Oxford.”

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

Key findings

The new air pollution data is published in the City Council’s Air Quality Annual Status Report, which provides an overview of annual averages for nitrogen dioxide levels across Oxford’s 71 air pollution monitoring locations.

The City Council has been monitoring and reviewing air quality in Oxford since 1999. In 2010, the whole of the city of Oxford was declared as an Air Quality Management Area (AQMA) and an Air Quality Action Plan (AQAP) was adopted by the Council in 2013.

Of the 71 locations monitored in 2019, seven were new monitoring locations. The remaining 64 sites were sites where air quality had been monitored from at least 2018. 

The Air Quality Annual Status Report is subject to approval by the Department for Environment, Food and Rural Affairs (DEFRA).

Some of the highlights of the Air Quality Annual Status Report are:

  • Across the 64 sites monitored in previous years, 70% showed increases of air quality levels; 16% measured the same levels as the previous year and only 9% showed slight decreases in NO2 values.
  • Six of the 71 sites monitored in 2019 were in breach of the annual legal limit.
  • NO2 levels in Oxford have decreased by 29% in the last decade.
  • For the first time, Cutteslowe Roundabout is compliant with the annual mean – in 2019 NO2 was 40μgm-3 - a 2.5% decrease from 41μgm-3 in 2018. However, further monitoring for another year is needed to establish if this is true decrease.
  • St Clements/The Plain continued to have the highest annual mean for NO2 with a value of 53μgm-3
  • Air pollution around the Westgate Oxford increased by 2μgm-3, again this is linked to the city wide increase due to weather.
  • High Street and St Ebbes automatic monitoring sites continued to be compliant with the legal limit, however St Aldate’s registered 42μgm-3, after being compliant in 2018.
  • At all locations which saw reductions in NO2 levels, on average the sites saw reductions of only around 1µg/m3, which is not statistically significant and is within the margin of error of the monitoring method. Realistically, this indicates that NO2 levels did not change in those areas in 2019.
  • Particulate Matter (PM2.5 and PM10) and Ozone (O3) were compliant with WHO guidelines in all measured locations in the city.

NO2 levels were still above the legal limit at six locations across Oxford:

Six monitoring locations in the city showed exceedances of the annual mean legal limit value for NO2 in 2019. This represents an increase of two sites when compared with the previous year, but down from a total of 17 sites just five years ago. Two of the exceedances are on St Clements.

The monitoring locations where the annual mean NO2 limit value was exceeded in 2019 are:

  • The High Street, where the NO2 annual mean was 50μgm-3 – an increase of 12% (from 44μgm-3 in 2018) – this has largely attributed to a combination of weather, construction work, and the resultant impact on traffic.
  • Long wall street, where NO2 was 41μgm-3 – an increase of 7.32% (from 38μgm-3 in 2018)
  • St. Clements Street 1 where NO2 was 53μgm-3 – an increase of 13.21% (from 46μgm-3 in 2018)
  • St. Clements Street 2 where NO2 was 42 μgm-3 – an increase of 14.3% (from 36μgm-3 in 2018)
  • George Street, where NO2 was 44μgm-3 – an increase of 4.5% (from 42μgm-3 in 2018)
  • St Aldate's, where NO2 was 43μgm-3 – an increase of 9.3% (from 39μgm-3 in 2018)

The biggest NO2 increases were in city centre locations, where air pollution is historically high and where pollutant build up and entrapment was higher during those extreme weather events.

New locations

The City Council monitored at seven new locations in 2019: Old Abingdon Road, Hollow Way road, Cowley Road/Union Street, Summertown Parade, Woodstock Road, Botley Road and an additional monitoring station on St Clement’s.

The new stations were added in order to gather more data from different locations within current hotspots (St Clement’s), and to further understand air pollution levels across the city at locations which may not have been monitored previously.
None of these locations experienced exceedances of the annual mean limit value for NO2.

The full air pollution report is available to view.