“…To the contrary, in countries in transition, levels of NO 2 and O 3 tend to increase due to the increased number of motor vehicles. Megacities where annual average NO 2 exceeded the WHO air quality criteria of 40 lg/m 3 were Beijing, Shanghai, Tokyo, Osaka, New York, Los Angeles, San Paulo and Mexico, while in New Delhi, Mumbai and Calcutta the annual average NO 2 concentrations were lower than 40 lg/m 3 [5]. Ozone and some of its precursors are transported long distances and across borders (transboundary movements) in the atmosphere, and so they can be considered to be a regional and even a global problem.…”