People migrate to cities due to different reasons such as easy access to schools, health facilities, jobs and transportation . More people, therefore, live in urban areas than in rural. According to the United Nations estimate, in 2014 more than 54% of the world population dwell in cities. It was 30% in 1950. Projections indicate that 66% of the world's population will live in urban by 2050 . Most of urban people reside in relatively small areas with high number of inhabitants per square meter of land (UN, 2015): " Close to half of the world's urban dwellers reside in relatively small settlements of less than 500, 000 inhabitants, while only around one in eight live in the 28 mega-cities with more than 10 million inhabitants. " It is ages since people noticed that urban air was different from rural air. However, it was air pollution which is the hallmark of the urban atmosphere. In 1818 Luke Howard (1772-1864) published the first edition of a book deal...
Urban Sustainability: Integrating Climate, Air Quality, and Resilience