For the first time in history, over half the world's population now live in cities. But only 12% of urban dwellers enjoy airborne particle pollution that meets World Health Organization (WHO) guidelines. Globally, lowest city air pollution is in Canada and Iceland and the highest in India (Delhi and Patna) and Pakistan (Karachi and Peshwar).

 

Half of the world's mega-cities have air pollution that is more than 2.5 times WHO guidelines, and in most places it is getting worse. Even in the wealthiest parts of the world, across Europe and North America, it is not clear that urban air pollution is getting better. The current emphasis on technical strategies to clean up our air is not working, and in some cases, such progress as has been made is being undone by other trends – Europe's increased use of diesel cars and more wood burning, for example.

 

Air pollution from cities also harms the people who live around them. The Chinese mega-cities of Beijing and Tianjin, as well as Karachi in Pakistan, cause more harm to the surrounding population than to their own residents. For other, more typical, mega-cities the impact of black carbon particles on people downwind can still be around 40% of that on the city residents. If the pollution resulting from chemical reactions downwind is considered, then impact on surrounding areas is greater still.

 

With growing urbanization, political leadership is needed to tackle this growing world health problem. More than ever we need to transform existing cites through design; reducing growing road transport dependency and providing clean home energy.