Air quality statistics in the UK 1987 to 2018

News published: 30/04/2019

The air quality statistics for 2018 are now finalised and summarise the concentrations of major air pollutants as measured by the Automatic Urban and Rural Network (AURN). These statistics cover annual average concentrations in the UK of particulate matter (PM₁₀ and PM_2.5), nitrogen dioxide (NO₂) and ozone (O₃).

They also include the number of days on which levels of any one of a set of five pollutants (PM₁₀, PM_2.5, NO₂, O₃ and SO₂) were ‘moderate’ or ‘higher’, according to the UK Daily Air Quality Index (DAQI).

The full Defra Statistical Release is available for download, highlights are as follows:

• Urban background and roadside particulate pollution (PM₁₀) has shown long-term improvement, with stable concentrations observed from 2015 to 2018 for both roadside and urban background sites. A substantial network for fine particulate matter (PM_2.5) has been operational since 2009 which shows a similar trend.
• The number of hours of moderate or higher levels of particulate matter (PM₁₀/PM_2.5) pollution has reduced in the long term, and a substantial decrease in number of hours of exceedance were recorded in 2018 compared with 2017 for PM_2.5 at both roadside and urban background sites.
• PM_2.5 pollution tends to peak in the winter months and in the evening, although there are many pollution sources. Burning of wood and coal by households in stoves and open fires is a large contributor to emissions of particulate matter both in the UK and across Europe, and is most common in winter months and during the evenings.
• Urban background and roadside nitrogen dioxide (NO₂) pollution has shown long-term improvement. In 2018 the lowest average annual mean concentrations since the start of the time series for both roadside and urban background monitoring sites were recorded.
• There were on average fewer hours of moderate or higher levels of nitrogen dioxide pollution in 2018 compared with 2017 at roadside sites. This continues a trend for reduction in short-term moderate or high NO₂ pollution since 2007, mainly due to reductions in this measure at monitoring sites in London.
• In 2018, NO₂ pollution tended to peak in the rush hours and during weekdays; particularly for roadside sites. Concentrations at roadside sites were 20 percent greater during the working week compared to the weekend. This pattern of concentrations follows the daily and hourly trends in road traffic.
• Urban background ozone (O₃) pollution has remained fairly stable between 2003 and 2018, although daily maximum eight-hour mean concentrations have shown a long-term increase since monitoring began. Rural background ozone pollution has shown no clear long-term trend. Concentrations increased from 2017 to 2018 at both rural and urban locations; reflecting the prolonged hot and sunny conditions in summer 2018.
  
• There were on average greater hours of moderate or higher levels of ozone pollution in 2018 compared with 2017 at both rural and urban background sites. This measure can vary greatly from year-to-year, and the hot summer in 2018 contributed to the high incidence of moderate or higher ozone pollution. 2018 had the greatest number of hours for this measure since 2006 for rural background sites, and since 2008 for urban background sites.
• In 2018, O₃ pollution tended to peak in the spring and summer months. Concentrations at rural background sites built up over the first few months of 2018, peaking in May before reducing to a stable level from August to the end of the year.
• There was on average a greater number of days of moderate or higher pollution at urban pollution monitoring sites in 2018 compared with 2017. This goes against the established trend of an ongoing decline in days of moderate or higher pollution at urban sites.
• There was on average a greater number of days of moderate or higher pollution at rural pollution monitoring sites in 2018 compared with 2017. There is no long term trend in this metric.
• The main drivers of the average number of days when air pollution is Moderate or higher are particulate matter and ozone, for urban and rural pollution monitoring sites in the UK respectively. In 2018, ozone was responsible for a large proportion of the moderate or higher pollution days. This was due to the prolonged hot and sunny conditions experienced in the UK in summer 2018.

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