CHAPTER ONE
1.0      INTRODUCTION
Gases, dust particles, water vapour and air contain microorganisms. There are vegetable cells and spores of bacteria, fungi and algae, viruses and protozoa cysts. Since air is often exposed to sunlight, it has a higher temperature and less moisture. So, if not protected from desiccation. Most of these microbial forms will die. Air serves as transport or dispersal medium for microorganism they occur in relatively small number in air when compared with soil or water. The microflora of air can be studied under two headings 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 cladosporiul and sporobolomyces, besides this two general, under general found in air are Aspergillus, Alternaria, Phytophthora and Erysiphe. The outdoor air also contains besidispores, ascopres of yeast, fragments of mycelium and canidia of molds. Among the bacterial genera Bacillus and clostridium, sarcina, mirococcus, corynebacterium and Achromobacter are widely found in the outside air, the number and kind of microorganism may very 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. In case of occupants being infected, the composition shows slight variations with latitude and to a lesser extent with attitude. The ozone owes its existence in the atmosphere to photosynthesis from oxygen under the influence of solar ultraviolet radiations. (Dr. Shiva, 2009).      
There is no microbes are native to the atmosphere rather they represent allochthonous populations transperted from aquatic and terrestrial habits into the atmosphere. Microbe of air within 300 – 1,000 or more feet of the Earth’s surface are the organisms of soil that have become attached to fragments of dried leaves, strain or dust particles, being blown away by the wind. Species vary greatly in their sensitivity to a given value of relative humidity, temperature and radiation exposure.
More microbes are found in air over land masses than far at sea. Spores of fungi especially Alterneria, Cladosporium, Penicillium and Aspergillus are more numberous than other forms over sea within about 400 miles of land in both polar and tropical air masses at all altitudes up to about 10,000 feet.