The issue of the environment has existed since ancient times, but has now become more intense and has brought about problems. However, up to a century before the trouble-making actions were not to the extent that could disturb the natural organization of the environment.
The ecological transformation was increased when the human population was concentrated in limited areas, and per capita demands and as a result the need of human communities to natural resources increased. With the advent and development of industry and then the industrial revolution since 1760, and the production of various products, the quality of human life improved as never before, and human beings headed toward a better and more prosperous life.
The revolution in industry and consumption led to the gradual emergence of environmental problems that were created by the daily decline of natural resources including renewable and non-renewable ones and the creation of various types of pollution in the environment, so that per capita demands of the Earth’s inhabitants are far greater than the growth of natural resources, and with the constant advancement of human beings and their supremacy over the nature, the level of encroachment on natural resources has increased, so far as the term "crisis" today replaces the “issue of the environment”. In general, the following three factors can be considered as effective in scarcity or decline of natural resources. 1) rapid population growth;
2) reduction of arable land, forests, ranges and pastures; 3) The unbridled use of new technologies and the failure of some of them to function without threatening natural resources.
Among the above factors, the rapid growth of the population and its disproportionate distribution on the Earth's surface are more important, because the next two factors are caused by the population's impact and its rapid rise and are basically defined by the failure to fulfil the major and minor needs of increasing populations, especially in some parts of the world. Therefore, one of the solutions to reduce the environmental crisis is controlling the population.
Considering the wide range of contaminants caused by the disturbance of the environmental balance such as air pollution, water pollution, noise pollution and soil contamination, this discussion only explores the population growth in the world and Iran and the air pollution crisis.