How safe is the air that we breathe? The VW diesel emissions scandal has highlighted the issue of air pollution.

The two pollutants which give most cause for concern are the toxic gas nitrogen dioxide (NO2) and particulate matter (PM2.5), particles so small they can be ingested deep into the lungs.

Earlier this year the UK's highest court ruled the government must take action to cut NO2 pollution. The UK has been in breach of EU limits for nitrogen dioxide for several years.