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Microbiology OF AIR
The air contains gases, dust particles, dried vapor droplets, in addition to these, air also contains more number of microorganisms. The air has vegetative cells and spores of bacteria, fungi and algae and protozoan cyst.  In the atmosphere, air mainly acts as dispersal or transport medium for microorganisms. When compared to soil or
water, air contains less numbers of microorganisms. The Microbiology of air can be studied under two headings such as outdoor and indoor microflora.
Outdoor microflora
The air in the atmosphere, which is found outside the buildings, is referred to as outside air.  The dominant microflora of outside air are fungi.  The two common genera of fungi are Cladosporium and Sporobolomyces.  Besides these two genera, other genera found in air are Aspergillus, Alternaria, Phytophthora and Erysiphe.  The outdoor air also contains basidispores, ascopores of yeast, fragments of mycelium and conidia of molds.Among the bacterial genera Bacillus and Clostridium, Sarcina, Micrococcus, Corynebacterium and Achromobacter are widely found in the outside air.  The number and kind of microorganisms may vary from place to place, depending upon the human population densities. Indoor microflora
The air found inside the building is referred to as Indoor air .  The commonest genera of fungi in indoor air are Penicillium, Aspergillus. The commonest genera of bacteria found in indoor air are Staphylococci, Bacillus and Clostridium. 
Sources of contamination
The major sources of contamination in the air are, automobile exhausts like incomplete combustion of fuel, agricultural sources like spraying of pesticides and insecticides, hospitals, industries like tannery industries, distilleries, nuclear power plants and chemical industries.  All these industries provide smoke into the air.  The smoke comprises of dust particles from the combustion of coal and oil.  Automobile engines driven by petrol, produce many different substances in its exhaust.  Some of these substances are serious air pollutants.  Air pol-
lutants are Co, CO2, unburnt hydrocarbon NO2, SO2 and lead from leaded petrol.