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Air pollution is not yet a thing of the past

Pollution face masks are not just for China. Dave Thompson/PA

It may seem odd for the European Commission to declare 2013 the “Year of the Air” in order to focus on improving air quality standards. Most would feel air pollution is a problem that has been more or less solved in Europe.

But a report for the Mayor of London published last week showed levels of harmful nitrogen dioxide at twice the World Health Organisation (WHO) recommended levels in Oxford Street and Brompton Road, two of the UK capital’s busiest shopping streets. A far cry from the notion that poor air quality is a thing of the past, or something associated only with megacities in developing countries.

Sulphur dioxide, nitrogen oxides and ozone

For some key air pollutants the outlook is good. Between 1990 and 2011, the 27 EU member states reduced their sulphur dioxide emissions (SO2), the primary cause for the acid rain that kills forests, by 82%. Most of these emissions come from fossil-fuelled power plants, whose pollution has been reduced by legislation. Consequently, the forested area damaged by acid rain in Europe has declined by more than 80%. With further SO2 reductions to be implemented, it is expected the problem will be limited to a few hot spots after 2020, for instance around the border between Germany and the Netherlands.

Nitrogen oxides (NO2 and NO, summarised as NOx) contribute to acidification and also cause direct health problems (NO2), including those arising from ground level ozone, which NOx helps to create. Again, these emissions stem from burning fossil fuels, in industry, homes, and transport. In the past 20 years an EU-wide reduction of 48% has been achieved, even as the volume of traffic has increased.

Reducing nitrogen oxides has also led to fewer peaks of extremely high ozone concentrations during European summers. In the summer of 2012, less than a third of monitoring stations exceeded the current EU threshold of 180 μg/m3 of ozone. However, in the same year, the EU’s long-term target (120 μg/m3) was exceeded in almost all EU countries and at 85% of monitoring stations.

These serious levels of ground level ozone indicate a key issue with air pollution. While reducing sulphur dioxide emissions can be directly associated with a reduction in acid rain, some of today’s main air pollution problems arise not from a single pollutant, but from complex interactions between them in the atmosphere.

Killer combinations

Ozone (O3) is formed primarily from nitrogen oxides and the so-called non-methane volatile organic compounds. These are generated partly from human activities such as the use of organic solvents, but there are substantial natural emissions too, such as isoprene and monoterpene emissions from forests and vegetation. Ozone formation only requires a mix of these components and sunlight, and as emissions are often dispersed far from the source, high ozone levels can occur in rural and remote regions away from urban areas most associated with air pollution.

The case is similar for what are called secondary aerosols, which contribute substantially to the concentration of fine particles in the air. SO2 and NO2 form aerosols with ammonia (NH3), mainly from agricultural sources such as farm animals, fertiliser and manure. Ammonia emissions have remained stable, showing only a small decline (~ 10%) over the past 20 years. The ammonium nitrates and sulphates that are created can be transported through the atmosphere across hundreds of kilometres, forming a background level of dangerous particulate matter.

Black carbon

Last but not least, primary emissions (in contrast to secondary formation of aerosols in the atmosphere) of fine particulate matter is a major cause for concern. These fine particles, typically defined by diameter (so that PM2.5 is particulate matter smaller than 2.5µm) can make their way deep into the lung and are known to cause respiratory and cardio-pulmonary diseases. PM2.5 is a product of combustion and especially road transport, with diesel engines being the main source of “black carbon” (dark, fine particulate matter, soot), classified as a carcinogenic substance by the WHO in 2012.

Overall, PM2.5 emissions have been reduced by 28% between 1990 and 2011, and are expected to decline further due to vehicle regulations. But in recent years many EU countries reported missing both EU target levels and the WHO’s more stringent guidelines. This means a large proportion of Europeans in urban areas are regularly exposed to harmful levels of particulate matter which cuts life spans of city dwellers by up to two years.

Particulate matter and ground level ozone are known to be very harmful to health, with air pollution being estimated to have killed 420,000 people in the EU prematurely in 2010. Ozone is known to also cause major damage to ecosystems and agricultural crops, reducing crop yields and affecting ecosystem services. Black carbon and ozone are “short-lived climate pollutants” which contribute to global climate change, despite their shorter lifetime than the likes of carbon dioxide or methane. Reducing emissions has tackled various environmental concerns over the last 20 years - the priority now has to be on addressing concerns over human health.

We need to focus on reducing those exposed to air pollutants, particulate matter and nitrogen dioxides, especially those most vulnerable groups such as children. Reducing emissions of black carbon and ground level ozone will improve human health and fight climate change, and this is a compelling case for action. In this context, the “Year of the Air” could not be more timely.

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