This book identifies air pollution in megacity areas as a serious environmental issue that calls for prompt countermeasures. The first book to compare air pollution in Mexican megacities to those in Japan, it examines air pollution trends for the past 50 years, mainly focusing on Mexico and Japan, but also including data from the US and China. It consists of 3 sections, discussing 1) air pollutants and formation mechanisms, 2) air pollution trends and contributing factors, and 3) Characteristics of air pollution in three Mexican Megacity Areas - Mexico City, Guadalajara and Monterrey. It also proposes co-beneficial countermeasure scenarios that can effectively improve regional and global atmospheric environmental conditions. Helping readers to understand air pollution formation mechanisms and countermeasure scenarios that are effective at both regional and global scales, the book appeals to researchers and graduate students in the field of atmospheric environmental science, as well as undergraduate science, engineering and social sciences students, and environmental administrative officers and anyone interested in our atmospheric environment.