The document discusses the composition of air and the presence of microorganisms within different atmospheric layers, primarily focusing on the troposphere and stratosphere. It highlights factors affecting microbial distribution, such as temperature, pressure, and UV radiation, and differentiates between outdoor and indoor microflora. The dominant microorganisms in outdoor air are identified as fungi and certain bacterial species, while indoor air is influenced by human presence and ventilation.

1. Dr C R Meera
Assistant Professor & HOD
Department of Microbiology
St. Mary’s College, Thrissur-20,
Kerala, India
Atmospheric Layers
&
Microorganisms in Air

2. Atmospheric Layers and Microorganisms in Air; Dr C R Meera, St.Mary’s College,
Composition of air
• 78 % Nitrogen
• 21% Oxygen
• 0.9% Argon
• 0.03 % Carbon dioxide
• 0.01% Hydrogen
• Traces of other gases
• Dust
• Condensed vapour
 Air also contains microorganisms.
 The study of airborne microorganisms is called
Aero microbiology.

3. Atmospheric Layers
• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere
• Exosphere.
 Troposphere is the atmospheric layer nearest to the earth surface
 Troposphere contains a heavy load of microbes
 Microbes liberated into air from other sources like soil, water, plant &
animal surfaces and human beings.
Atmospheric Layers and Microorganisms in Air; Dr C R Meera, St.Mary’s College,

4. Factors affecting distribution of microbes in Troposphere
 Decrease in temperature with increase in height
• Top layers of the troposphere - 43 to - 83 degree Celsius
 Reduction in atmospheric pressure
 Reduction in concentration of oxygen
 Decreased water availability
 High intensity of light radiation and UV radiation
• Cause lethal mutation and death of microorganisms.
 Low concentration of organic carbon which will affect the growth of heterotrophs.
 High altitude limit even the existence of autotrophs.
Atmospheric Layers and Microorganisms in Air; Dr C R Meera, St.Mary’s College,

5. Factors affecting distribution of microbes in Stratosphere
 Stratosphere - Atmospheric layer
above the troposphere
 Low mixing of gases
 Contains layer of high ozone
concentration
 High concentrations of ozone and UV
radiation are detrimental to microbes
 Stratosphere- A barrier to the
transport of living microorganisms to
or from the troposphere.
Atmospheric Layers and Microorganisms in Air; Dr C R Meera, St.Mary’s College,

6.  Micro flora in air is less compared to soil and water
 Air is mainly acting as the transport or dispersal media for microorganisms.
Microorganisms are mainly confined to the troposphere.
 Vegetative cells and spores of bacteria
 Fungi
 Algae
 Viruses
 Cysts of protozoa
 Exposed to sunlight- Higher temperature and less moisture content
Microorganisms in Air
Atmospheric Layers and Microorganisms in Air; Dr C R Meera, St.Mary’s College,

7.  Outdoor air- Air outside the buildings
 Indoor air- Air inside the buildings
 Outdoor microflora- Microorganisms in outdoor air
 Indoor microflora- Microorganisms in indoor air
Air Micro flora
Air Micro flora
Outdoor
Micro flora
Indoor
Micro flora
Atmospheric Layers and Microorganisms in Air; Dr C R Meera, St.Mary’s College,

8. Outdoor Micro flora
 Dominant micro flora in the outdoor air - Fungi
• Deuteromycete Cladosporium and the Basidiomycete yeast Sporobolomyce
• Basidiospores, Ascospores, conidiospores and mycelial fragments
 Bacterial forms
 Spore forming species like Bacillus, Clostridium
 Non spore formers like Sarcina lutea, Micrococcus luteus
 Non pathogenic species of Corynebacterium and Coliforms
 Air microflora over the sea surfaces - Achromobacter, Bacillus,
Corynebacterium, Flavobacterium, Micrococcus, Sarcina and Staphylococcus
 Spores are dominant than vegetative forms at high altitudes
Atmospheric Layers and Microorganisms in Air; Dr C R Meera, St.Mary’s College,

9. Factors Affecting Outdoor Micro flora
 As altitude increases- low temperature, UV radiation and desiccation
 Human population densities
• More microbes are found in crowded areas
• Microbes more in air over terrestrial surfaces then over the sea
 Variations in the spore densities in outdoor air occur on an annual and
daily basis
 Diurnal fluctuation in spore liberation also affects outdoor microflora
 Eg: Colorless basidiospores- liberated usually during night
 Sporangia of Phytophthora - liberated in the morning
 Spores of Erysiphe - liberated in midday
Atmospheric Layers and Microorganisms in Air; Dr C R Meera, St.Mary’s College,

10. Indoor Microflora &
Factors Affecting Indoor Micro flora
Atmospheric Layers and Microorganisms in Air; Dr C R Meera, St.Mary’s College,
 Affected by air circulation through doors, windows and by
turbulence caused by moving people
 Dominant micro flora in the Indoor air- Fungi
 Penicillium and Aspergillus
 Bacteria in indoor air - ventilation and the number of occupants in
the room
 Common bacterial forms
 Bacillus, Staphylococci and Clostridium perfringens
 Indoor bacteria is mainly from human skin and respiratory tracts
 Pathogenic bacteria or viruses - from infected occupants

11. Atmospheric Layers and Microorganisms in Air; Dr C R Meera, St.Mary’s College,