Atmospheric Air and Dust

Air is made up of a mixture of different gases and material from natural processes such as wind erosion, evaporation from the sea, earthquakes, and from human activity in the form of combustion products from processes and vehicles. 

The size of particles is often indicated in pm (microns). 1 p,m = l(H m. Particles in the atmosphere vary, from particles less than 0.01 pm up to leaves, ind insects. 

Studies of atmospheric particles show that their distribution is often birno-dal i.e., the particles are made up of rwo separate fractions, one with fine and one with coarse particles (Fig. 9.1). The coarse particles, from about 2.5 pm upward, are made up of natural dust from the effect of wind, erosion, plants, volcanoes, etc. The finer fraction is made up of particles smaller than 2.5 pm and consists primarily of particles from human activity, combustion, traffic, and processes. 

Hygiene requirements for particle concentrations in the air have been based on concentrations of particles smaller than 10 pm (particulate mass, P.M,)). Studies have shown a direct connection between the death rate and finer particles, and official requirements are under review, in both Europe and the United States, to be based on the concentration of particles smaller than 2.5 pm (PM2.5). 

To effectively eliminate these small particles and fulfill official requirements, finer filters are needed, and the requirement for filtering of outdoor air, recycled air, or exhausted air is increasing. With an F7 (EU7) filter, good separation of small particles is achieved. 

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