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.

9.2.2.1 Sire of Particles

The size of particles is often indicated in pm (microns). 1 firri = 10~6 m. Particles in the atmosphere vary, from particles less than 0.01 ^m up to leaves and insects.

Studies of atmospheric particles show that their distribution is often bimo — dal; i. e., the particles are made up of two separate fractions, one with fine and one with coarse particles (Fig. 9.1). The coarse particles, from about 2.5 p-in 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 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 p, m (particulate mass, PM10). 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 |xm (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.

9.2.2.2 Number of Particles

The number of particles varies considerably with time and place (Table 9.1). To reduce the number of particles in the urban environment to the same number as in the countryside, a filter with 99.9% separation is required. An

Atmospheric Air and Dust

Spores, living or dead bacteria, dust, diesel fume, cigarette smoke, etc. Tests have shown that an F7 (EU7) filter can effectively reduce allergens in the air. 2

Carcinogenic Potential of Pollutants

It is known that the urban traffic environment is carcinogenic due to auto­motive gases and polyaromatic hydrocarbons. An F8 (EU8) filter reduces their effect by 80% .2

OdorslGases

A large number of odors are borne by particles, but for effective separa­tion, chemical filters are very often required, which can be justified in an ur­ban environment.

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