Theory

• Atmospheric pollution is caused by the release of particles and noxious gases into the atmosphere and this can have a negative effect on human health.
• In 2014, the WHO found that urban air pollution was 2.5 times higher than the recommended levels in about half of the urban populations being monitored. Air pollution accounts for a estimated 4.2 million deaths per year due to stroke, heart disease, lung cancer and chronic respiratory diseases.
• Around 91 per cent of the world's population lives in places where air quality levels exceed WHO limits.
• Human activity produces the pollutants but it is primarily the weather that determines what will happen once they are released into the air. During wet or windy conditions pollution concentrations remain low, either blown or washed away. During periods of still, hot weather, pollution is able to build up to harmful amounts, leading to what are known as pollution episodes.