Guidelines for performance

Problem 3.1. Determine priority chemical substances in atmospheric air and investigate their adverse impact on human health.

Throughout the life people are constantly feeling the effects of various chemical substances, which can cause various types of diseases, health disorders, as well as injury at the time of contact and after a certain period of time, Fig.3.1.

Fig.3.1. Overview of main health effects on humans from some common types of pollution

World economy annually emits more than 15 billion tons of carbon dioxide, 200 million tons of carbon monoxide, more than 500 million tons of hydrocarbons, 120 million tons of smoke and others. The total amount of emissions to the atmosphere is more than 19 billion tons.

Air pollution is quite crucial, because the most part of harmful substances penetrate into human body by respiratory ways.

Air pollution is the release of chemical substances, particulate of mater (PM) and biological molecules into the Earth's atmosphere. The substance can be solid particles (particulate matter are characterized by their micrometer size – PM_2.5, PM₁₀), liquid droplets, or gases. Also air pollutant can be of natural origin or man-made.

Basic sources of anthropogenic pollution are the industry and transport, Fig.3.2.

Common gaseous air pollutants include carbon monoxide (CO), sulfur oxides (SO₂, SO₃), nitrogen oxides (NO_x), hydrocarbons and particulate matter, which are respectively the products of fuel combustion, Fig.3.3.

Adverse effects of pollutants are characterized by changes in the environment, including climate change, causing significant adverse consequences for human health and for the structure, regenerative abilities and productivity of natural ecosystems. Air pollution adversely affects human health and can be a reason of such diseases as inflammation of the respiratory tract, disfunction of lungs and in some cases even makes for the death.

a b

Fig.3.2. Annual emissions of carbon monoxide (a, 2900 t/y)
and nitrogen oxides (b, 40-50 t/y) from basic sources of air pollution

Fig.3.3. The main sources of atmospheric air pollution by ozone, nitrogen dioxide and particulate matter

During the last decade a lot of studies are also focusing on adverse effects of nitrogen oxides (NO_x) and particulale matter (PM) emissions, as initiators of ozone deterioration, photochemical smog, regional haze, acid rains which have further direct impact on human health.

These admixtures when getting in human's organism cause oxidation-reduction balance disturbance in the respiratory system. As a result the balance between oxygen forming process and ability of biological system to render reactive intermediate metabolites is disturbed. Oxidation-reduction balance disturbance can cause toxic poisoning as a result of emergence of peroxide and free radicals that damage all cell components, including proteins, lipids and Deoxyribonucleic acid (DNA).

Nitrogen dioxide source is processes of fuel combustion, in which air is an antioxidant:

N₂ + 2O₂ → 2NO₂

NO₂ is an important reagent in atmospheric processes and causes forming ozone and other highly active reaction products – nitric acid, sulphuric acid, sulphates and organic aerosols (organic aerosols can be rated as PM₁₀, PM_2.5 with diameter 2.5 - 10 μm).

The important photochemical reaction is:

NO₂ + О₂ + hν→ NO + O₃

Population health risk from nitrogen dioxide effect is caused by both direct NO_х effect, and its reaction products – ozone (O₃) and particle matter (PM₁₀, PM_2.5).

Short-term concentrations of nitrogen dioxide causes inflammation of respiratory tracts, and according to the research the limit value for this effect type should not exceed 85 μg/м³. Long-term nitrogen dioxide concentrations cause disturbance of pulmonary function and respiratory symptoms.

Recent research confirms a short-term ozone effect on human's organism, by force of analysis of correlation «response-action».

The short-term ozone effect causes disturbance of the respiratory symptom, pulmonary function, and also pneumonia, increase of sickness rate and mortality. Epidemiological research of short-term ozone effect gives an opportunity to define its limit value for population level.

PM is a complex mixture of solid and liquid particles of organic and inorganic substances suspended in the air. The particles are identified according to their aerodynamic diameter, as either PM₁₀ (particles with an aerodynamic diameter < 10 μm) or PM_2.5 (aerodynamic diameter < 2.5 μm). The major components of PM are sulphate, nitrates, ammonia, sodium chloride, carbon, mineral dust and water.

The effects of PM on health occur at levels of exposure currently being experienced by most urban and rural populations in both developed and developing countries. The mortality in cities with high levels of pollution exceeds that observed in relatively cleaner cities by 15–20%.

Nature and consequences of PM effect on human respiratory and cardiovascular systems depend on aerodynamical diameter of these particles (Fig.3.4).

Fig.3.4. The consequences of PM effect on human respiratory and cardiovascular systems

PM size is the main determiner for the particles precipitation place in human respiratory tracts:

· Particles with diameter more than 10 μm are filtered in the nose and gullet and are not a threat for human health;

· Particles with diameter less than 2.5 μm precipitate in lungs and bronchial tubes;

· Particles with diameter less than 10 μm get into interchange of gases zone in lungs;

· Very small particles, with diameter less than 100 nanometres, through lungs and cell membranes can get into blood circulation system and influence other organs.

Adverse impact of fine PM_2.5 is an actual problem leading to high plaque deposits in arteries, causing vascular inflammation and atherosclerosis –a hardening of the arteries that reduces elasticity, which causes heart attacks and other cardiovascular problems. Recent results suggest that even short-term exposure at elevated concentrations can significantly contribute to heart disease. Small particles with diameter less than 100 nanometres are the cause of considerable deterioration of blood circulation system functioning. These small particles can get into brain and cause progression of Alzheimer's disease.

Atmospheric air pollution by contaminants, first of all, influences the levels of population sickness rate. Quantitative population sickness rate dependences on intensity degree of factor, when they are isolated and combined, are denoted in the works.

To estimate atmospheric pollution danger and fix its maximum concentrations for different periods of the effect, dependence between substance concentration and time of biological effect exposure is used, for example as:

(3.1)

where C is the concentration that provokes standard effect in action process during time T; C₀ is the concentration that provokes the same effect during the time equal to established unit; a is the angulation of straight line to time axis (that defines duration of pollution effect).

Degree of real danger of some factors impact on health, the way population feels and human vital activity depend on:

· Aggression of the factor (toxicity for chemical pollution);

· Scope of spreading in residenctial zone;

· Intensity level;

· Effect duration.

The higher is a value of each component, the higher is a degree of population health factor danger. That’s why estimation criteria of the adverse effect of air-transport processes should take into account all mentioned features.

The toxicity of a substance depends on the following factors: dose and concentration of the substance; physical and chemical properties of material; ways and speed of penetration of substances into the human body (organism). The dose can be toxic or fatal. Toxic dose causes pathological changes in physiological functions of human body, but does not lead to death. For comparative evaluation of substances toxicity a value of lethal dose (LD) is used. In toxicology, the median lethal dose, LD ₅₀ (abbreviation for "lethal dose, 50%"), LC₅₀ (lethal concentration, 50%) of a toxin, radiation, or pathogen is the dose required to kill half the members of a tested population after a specified test duration.

Problem 3.2: Calculate the maximum short-term concentration of air pollutant produced by emissions of hazardous production facility under specified and adverse weather conditions (Table C.1). Calculate at which distance from hazardous production facility maximum concentration of harmful substance will obtain maximum permissible concentration.

Дата добавления: 2015-11-16