Pollution can take many forms.
Air, water, solid waste - most agree that pollution is harmful for people and other life on Earth. But more controversial is how to best prevent it - and clean it up.
Client Earth has taken the UK government to court for allegedly failing to tackle a crisis in air quality. The nonprofit says the government has downplayed the role of diesel emissions in causing high pollution levels in cities like London. Nik Martin traveled to the English capital to meet with some clean air campaigners trying to bring about change.