Outdoor Air Pollution
The most well-known and dangerous outdoor air pollution type is smog: the artificial fog that covers many metropolises around the world as a combination of industrial emissions, car exhaust and other pollutants present in the atmosphere. Such outdoor air pollution is more difficult to cope with during the warm months of the year, with the mention that for every city, there is a certain specificity in terms of pollution causes. Factors that influence such differences vary from the weather characteristics to geographical specificity; thus even within the same area, outdoor air pollution may be spread differently. Temperature inversion is the most serious of issues under the circumstances.
Due to this phenomenon the cold and polluted air remains trapped at the ground level without the possibility to get dispersed in the higher strata of the atmosphere. Therefore, outdoor air pollution is an increasing problem of most large industrial cities all over the world. Even if the city is located in an area surrounded by mountains, it still doesn't help much since the pollutants remain trapped over the city. Such temperature inversions responsible for the smog formation appear throughout the year regardless of the season, though summer is the harshest to cope with.
One direct consequence of outdoor air pollution is the appearance of acid rain. Sulfuric acid as an atmosphere pollutant can easily combine with the rain drops or the snow and acidify them before their falling on the ground. The consequences of acid rains on the environment are sheerly horrifying, killing trees and plants alike, destroying the soil and changing the natural chemistry and the ecosystem balance in surface waters: lakes, rivers and oceans. It goes without saying that wildlife will suffer accordingly from the effects of outdoor air pollution, but humans will not remain unharmed either as we need the soil, the water and the air to survive just like the rest of the life forms on earth.
Another environmental issue triggered by outdoor air pollution is the greenhouse effect, also known under the much debated name of global warming. Gases like carbon dioxide build up in the atmosphere without being processed by plants. Normally the green world would turn carbon dioxide into oxygen continuously cleaning and freshening the atmosphere, but the fuel exhausts and the industrial emissions are far too large for the forests to absorb all of them. Heat is trapped every day closer to the earth's surface, and a global rise in the temperature would cost us dearly in terms of the planetary ocean level and hurricanes that we cannot escape from.