Key words: Aerosol microclimate, aerosol, dispersion system, aerodynamic particle diameter, particulate matter, fog, spray

AEROSOL MICROCLIMATE

Aerosol microclimate is a component of an internal environment formed by aerosol flows that co-create the overall state of the internal environment.

Aerosol is a special type of dispersion system consisting of a gaseous phase and solid or liquid particles dispersed therein.

The dispersion system is a system of at least two types of phases, one phase (the disperse phase) being dispersed in the other (dispersing medium).

The dispersed phase material is formed by dispersing particles of a team.

The aerodynamic particle diameter is the particle diameter at a density of about 1 g/cm3 falling stalling speed caused by gravity at a steady temperature, pressure and humidity.

Solid particles of PM₁₀ (particulate matter) contain particles with a particle size of 2.5 to 10 μm, with 50% of these particles having an aerodynamic diameter of 10 μm.

Solid particles of PM_2,5 (particulate matter) contain particles with a size of 2.5 or less, with 50% of these particles having an aerodynamic diameter of 2.5 μm.

Aerosols are made up of solid particles (dust) or liquid particles (fog). Solid aerosol are electrically charged positive or negative, with a size of 0.1 to 100 micrometers. In the outdoor air of the city, dust falls within the range of 1100 t/km² per year at a standard concentration of 1 to 3 mg/m³.

Domestic dust, especially biological particles below 1 micrometer, are the main cause of asthma affliction. The permissible value in normal buildings is the concentration of inert solid aerosols of 10 mg/m³.

DISTRIBUTION OF AEROSOLS

Aerosols can be divided into solid aerosols and liquid aerosols. Solid aerosols or dust can be classified according to their origin by organic (animal or plant origin), inorganic (metallic or non-metallic) and mixed.

Dust particles of plant and animal origin are lighter than the inorganic particles. These particles are mostly fibrous, branched in tufts. While the inorganic particles are prismatic or spherical in shape with smooth or sharp edges. The process of sedimentation of dust particles is influenced by the earth's attraction, air resistance and the electrical polarity of individual material surfaces. Aerosol particles are microbial transporters.

The best known example of a liquid aerosol is the fog that is formed by the condensation of water vapor when the temperature drops below the dew point. Other liquid aerosols are produced in industrial plants. According to the composition, liquid aerosols may be either monodisperse (particles of approximately the same size) or polydisperse (particles of different sizes).

According to the particle size, there are vapors (particles less than 10-4 mm) and sprays (particles larger than 10 mm). Immediately after its formation, the liquid aerosol particles change their shape, which is due to the evaporation of the fluid or the influence of particle aggregation.

According to the shape of the dispersed particles can be divided aerosols corpuscular, laminar, and fibrillar disperse systems:

• Corpuscular dispersion systems consist of isometric dispersion particles whose dimensions are approximately the same in all three spatial directions.
• Laminar dispersion systems (mineral particles of bentonite and kaolin) and fibrillary dispersion systems (natural and synthetic fibers of inorganic or organic nature) have anisometric particles. One or two of these dimensions predominate in such particles and belong to di-form systems.

BIOLOGICAL EFFECT OF AEROSOL CLIMATE

The effect of an aerosol microclimate depends primarily on the flow of aerosol particles, the exposure time, the concentration, the chemical composition and the physical properties. Physical characteristics include particle size, shape and strength, electrical charge, solubility in biological fluids, and others.

The effects of aerosol particles on the organism can be characterized in terms of physical (mechanical properties), chemical (toxicity), physico-chemical and biological (allergy and carcinogenicity).

Aerosols act mechanically on the skin, in the conjunctival sac, on the mucosa, block the lymphatic pathways in the lungs and the like. Longer exposure is irritating and results in nonspecific inflammatory changes of the skin, conjunctiva and mucous membranes depending on the chemical composition of the particles, their amount, size, shape, depth of action and individual response.

CRITERIA OF AEROSOL MICROCLIMATE

There are no criteria that would be able to determine the maximum allowable flow of aerosol to the organism. Most regulations set the maximum allowable concentration of aerosols in the air. In outdoor air for dust with a maximum SiO₂ content of 20%, an average daily concentration of 0.15 mg/m³ is permitted and the fall of dust may not exceed 150 tonnes per km² per year.

OPTIMIZATION OF AEROSOL MICROCLIMATE

Optimization of the aerosol microclimate can be accomplished by interfering with an aerosol source or by interfering with the transfer field.

Intervention to the source of aerosols can be done in three basic ways:

• Change of technology already in preparation for operation
• Mixing bulk material with other suitable substances, such as water
• Closing the source with a solid cover or liquid screen
• Interference with the aerosol transfer field can be accomplished:
• Limiting aerosol dispersion in the building (vertical or horizontal distribution)
• Ventilation
• Air filtration through filters in air handling units
• Coagulation of aerosol particles (by spraying a liquid aerosol with high wettability, small particles are merged into larger ones that settle down due to gravity)

The last measure against aerosols is the use of protective equipment such as glasses, respirators and suits. These protective aids are extremely inconvenient. Their use should only be exceptional. There are workplaces where we can not do without them - eg paint shops, chemical plants, operating theaters, mining and textile factories, and others.