In contrast,  \cite{Chen_2008} suggests that countries in transition have shown that traffic related air pollutants such as NO2 and SO3 tend to increase due to the increasing number of motor vehicles. Mega cities such as Beijing, Tokyo, Osaka, New York, Los Angeles and Sao Paulo have recorded NO levels that exceed the WHO air quality criteria of 40\(\mu\)g/m3.  Recently, the report 'State of Global Air/2017', estimates that for the world's population (90%) that reside in areas with unhealthy air, 50% of them live in areas where the PM2.5  concentrations were above the WHO Interim Target 1 (IT-1 of 35\(\mu\)g/m3) whilst 64% reside in locations exceeding Interim Target 2 (25\(\mu\)g/m3). Almongst the countries that have recorded extreme concentrations (above 75\(\mu\)g/m3) were China, India, Bangladesh and Pakistan as shown in Figure 3. In these countries the sources of this extreme PM2.5 concentrations were due to combustion emissions from multiple sources, including household solid fuel use, coal-fired power plants, agricultural and other open burning and transportation and industrial related sources. The lowest concentrations of the annual average population-weighted PM2.5 (\(\le\)8\(\mu\)/m3) were recorded in Finland, Australia, New Zealand, Canada, Brunei Sweden, Greenland and several Caribbean and Pacific Island countries \cite{institute2017}.