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Atmosphere

UK air is cleaner but challenges remain

17 Oct 2019
Air pollution
(Image courtesy: CC0_Pixabay)

Take a deep breath. If you’re a long-term UK-dweller the air in your lungs right now is almost certainly fresher than the air you inhaled forty years ago. Policy interventions in the UK have significantly improved air quality since the 1970s, according to a new study, and resulted in a halving of the number of deaths attributable to some of the most common air pollutants. But there are significant challenges associated with reducing secondary pollutants such as ozone; the study suggests where the UK needs to focus its clean-up act next.

Outdoor air pollution is estimated to kill 4.2 million people each year worldwide. In the UK around 30,000 deaths a year are attributed to air pollution. Long-term exposure to air pollution increases risk of cardiovascular and respiratory disease and lung cancer. Short-term exposure aggravates respiratory and cardiovascular illness and triggers asthma attacks. There is also emerging evidence of links between air pollution and diabetes, obesity, cognitive decline, dementia and adverse birth outcomes.

Like most other industrialised countries, the UK saw a rise in air pollution through much of the 20th Century, reflecting an increasing demand for energy and mobility, and a fall in air pollution in recent decades due to more stringent emissions standards. But how much impact did policy interventions really have?

Stefan Reis from the Centre for Ecology & Hydrology in Edinburgh and colleagues at the University of Edinburgh, University of Oxford and Institute of Occupational Medicine modelled changes in key air pollutant concentrations — nitrogen dioxide, sulphur dioxide, fine particulate matter and ozone — and related health effects across the UK over the last 40 years.

In order to correct for the variability caused by meteorological factors, they used a fixed meteorological year for all simulations. This meant that the modelled changes in air pollutant concentrations and related health effects were solely a function of changes in emissions, and reflected the impact of policy interventions such as phasing out specific fuels or substances, regulating use of particular chemicals, or developing cleaner and more efficient technologies.

Overall, the results show that the UK attributable mortality due to exposure to fine particulate matter declined by 56% and that due to nitrogen dioxide exposure dropped by 44%, while ozone attributable respiratory mortality increased by 17% over the same period (with a slight decrease between 2000 and 2010).

Analysing the data more closely, it was clear that policy interventions and reductions in emissions were behind many of the trends. For sulphur dioxide and fine particulate matter, the researchers observed a consistent downward trend over the entire time period. Nitrogen dioxide was more complicated. Growth in vehicle numbers and miles travelled resulted in an increase in NOx emissions between 1970 and 1990, but then more stringent vehicle emissions controls kicked in and emissions began to fall. “The further growth of vehicle numbers and mileage has been offset by individual vehicles emitting less,” says Reis.

Ozone concentrations showed a steady increase over the 40-year period; ironically some of the greatest increases have occurred in areas where NOx emissions have decreased most. That’s because ozone is a secondary pollutant that forms from precursor pollutants including NOx and non-methane volatile organic compounds (NMVOCs). The ratio of nitrogen dioxide to NMVOC determines how much ozone is produced.

“Too much nitrogen dioxide leads to destruction of ozone, so you will typically not find high ozone concentrations on or near busy roads, but rather some distance away from the main sources, where the atmosphere is more mixed,” says Reis, whose findings are published in Environmental Research Letters (ERL).  “To reduce ozone further, consistent reductions of NOx and NMVOC emissions will be essential, so the current focus on reducing road transport emissions and more general fossil fuel combustion is on the right track.” Ozone can also travel long distances and so it will be important to look at sources outside the UK.

Reis and his colleagues suggest that there needs to be a greater focus on reducing emissions in sectors that have so far escaped major scrutiny. These include agriculture, domestic wood and coal burners, shipping and non-road mobile machinery. The researchers also note that we need to better quantify the sources contributing to the pollution and focus on a truly integrated assessment of policies to avoid unintended consequences. For example, the promotion of biomass for domestic heating has helped to reduce our carbon footprint but has also led to local air pollution hotspots because most domestic appliances do not have filters and can emit large amounts of fine particulate matter.

“Integrated policies that look at air pollution, greenhouse gases and other sustainable development indicators are essential to ensure interventions are leading to overall improvements, rather than solving one problem by creating new ones,” says Reis.

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