Air Microbiology (Aeromicrobiology)
Since the air does not, under normal conditions, contains the nutrients and moisture for growth, maintenance and multiplication of microorganisms, it could not be considered their natural environment. Nevertheless, air normally abounds in their numbers as microorganisms gain entry into it from soil and other dry decomposed material including excrete exposed to the action of wind. Air-borne microorganisms becomes an important source of contamination in laboratories, hospitals, industries, and of exposed food material and drinks. Depending upon the nature of microorganisms, some contaminations may cause spoilage of contaminated products and diseases when ingested. By mere sneeze and cough, infection from mouth and lungs may be discharged into the air around. In view of this, knowledge of quantity and quality of air microorganisms seems essential because we need pure air for respiration.

In still air, the microorganisms tend to settle down quickly with their carriers leaving the air fairly free of them. The air after heavy rains is fairly free of microorganisms. Development even of slightest current can keep the microorganisms suspended in air for protracted period of time. In general, air above the warmer regions of earth harbours greater number of microorganisms
 than the above cooler regions provided adequate humidity is present. Inadequate ventilation of inhabited buildings promotes greater accumulation of microbial number in the air space. The air of an uncrowded and not heavily industrialized mountainous regions and oceans is considered pure and good for health as it is relatively free from microorganisms.