Air Pollution I Overview PDF

Air pollution I – overview of air pollution Ekaterine Ruadze, MD, MSc, PMP Air pollution The AIR Pollution is the result of emission into the air of hazardous substances at a rate that exceeds the capacity of natural processes in the atmosphere to convert, deposit or dilute them. One can speak ab...

Air pollution I – overview of air pollution Ekaterine Ruadze, MD, MSc, PMP Air pollution The AIR Pollution is the result of emission into the air of hazardous substances at a rate that exceeds the capacity of natural processes in the atmosphere to convert, deposit or dilute them. One can speak about the microbiological air pollution as well as radioactive compounds of air and chemical pollutants in the air. Some facts of air pollution In 1990, worldwide almost 100million tons of sulfur oxides, 68 million tons of nitrogen oxides, 57 million tons of suspended particulate matter (SPM) and 177 million tons of carbon monoxide were released in to the atmosphere as a result of human activity. Inversion The accumulation of chemically active compounds in the atmosphere is greatly affected by land features and atmospheric movements. Valleys, nearby mountain ranges, and the lack of open space strongly increase the severity of air pollution. In an inversion temperature rises which increasing altitude rather than falling, which is normally the case. The inversion layer is a mass of air with inverted temperature gradient. The motion of air in an inversion layer is suppressed and it limits the mixing and dilution of air pollution. Inversions are very common especially in valleys and coastlines. Inversion layer Aerosols Small solid and liquid particles (fine drops and droplets) that are suspended in air form a mixture called aerosols. Aerosols consist of a mixture of solid-phase particles, combination solid and liquid-phase particles and sometimes liquid droplets suspended in air. Dust is a settled or deposited aerosol which consists of particles in the solid phase. When they are up in the air, the particles are called the suspended particulate matter. This term is usually reserved for particles that are created by dry process and are chemically and physically unchanged from the original material except for their size. Aerosols Smoke is very complicated chemically and varies in composition depending on what has been burned. Smoke consists in particles in both the solid and sometimes liquid phase and the associated gases that result from combustion. Ash is the solid phase of smoke, particularly after it settles into a fine dust. Fumes are polydispered fine aerosols consists of solid particles that often aggregate together, so that many little particulates may form one big particle. Aerosols - size The most important characteristic of aerosols that determine their behavior are: SIZE and COMPOSITION. The individual particles in aerosols may be relatively uniform in size and are called monodispersed. Aerosols with particles with highly variable in size are called polydispersed. In nature all aerosols are polydispersed. The size is related to the mass: the smaller the size the less the mass. Particles form different sources have different size distribution. Aerosols - size The size measurement of particle that reflects the behavior of a particle more accurately than a physical measurement would is called aerodynamic diameter and defined as: the diameter of a sphere with a density of 1000kg/m3 with the same settling velocity as the a particle of interest and it is measure in micrometers. The effect of particles on the body reflects the efficiency with which they penetrate all the way to an within the lung and their chemical reactivity and toxicity once they arrive. https://www.youtube.com/watch?v=Cc-IT6wh4JQ Aerosols - size Particles above 100 µm may be source of irritation to the mucous membranes of the eyes, nose and throat but hey do not get much farther. Particles larger than about 20 µm generally do not enter the lower respiratory tract, below the throat. Those particles below the 20 µm comprise the thoracic fraction because that high proportion can penetrate into the lungs. The particles below the 10 µm enter the airways with greatest efficiency and may be deposited in the alveoli or airspaces. Aerosols - size Particles between 10 µm and 2.5 µm are called coarse particles ; Particles below the 2.5 µm are deposited in the alveoli with very high efficiency and are called fine particles. Particles below the 0.1 µm are called ultrafine particles. These particles tend to remain suspended in the air and be breathed out again unless they carry an electric charge. The air pollution is predominantly/mainly in the coarse and fine range, which is called reparable range (10 µm – 0.1 µm) Aerosols – shape Shape is important in determining the effects of a particle. The human body handles longer and thinner particles, called fibers, differently form particles that are more rounded in shape. Fibers are more difficult to remove from the lungs by natural protective mechanisms. Fibers are described by the ratio of their length to their width. A particle at least five times longer than it is wide is considered to be a fiber. Long and thin shape of fibers of asbestos are particularly damaging to the lung and can cause lung cancer and mesothelioma of the pleura. Aerosols – composition Liquid constituents of air pollution exist as aerosols, either as liquid-phase particles, which are droplets, or in association with solid-phase particles. Liquids that are constituents of air pollution are always water- based, because droplets of more volatile organic compounds evaporate to the gaseous phase very quickly. A cloud or dense collection of droplets is called mist. Liquid and gas-phase constituents are often attracted to and ride on the surface of solid particles – this is called adsorption. Aerosols – composition The humidity in the atmosphere is an important determinant of the water content of particles: the lower the humidity the faster the water evaporates. When particle is reduced to a solid phase it becomes a droplet nuclei. Dry particles may also take on water when they are released into a humid atmosphere. The small particles those absorb the large amount of water are called hygroscopic. Through this absorption the mass is added to the particle and its capacity to carry other dissolved constituents may be increased. Aerosols - composition The evaporated compound in the gas phase is called a vapor and behaves like a gas in air pollution. Droplets may also form from condensation of vapor in a saturated atmosphere. Fog is a common example of this. Gases Air pollution can also consist of gaseous constituents, the properties of greatest importance being solubility in water and chemical reactivity. Solubility is a major determining factor of the health effects of gases. Solubility for gases is much like size for particles: it is a characteristic that determines the efficiency with which they penetrate deeply into the respiratory tract. Gases A gas that is soluble in water will be dissolved in the water coating the mucous membrane of the lungs and upper respiratory tract and will be removed from air passing more deeply. A gas that is insoluble in water will not be so removed and will penetrate to the alveoli, the deepest structures of the lung, more efficiently. Gases that are reactive tend to have their major effects on the airways rather that the alveoli. They may irritate the walls of the airway and cause bronchitis or induce asthmatic attacks. Gases Many gases such as ozone and sulfur dioxide, adsorb onto the surface of particulates and penetrate deeply into the respiratory tract in this way. When this happens, the effects may be different and greatest than exposure to either the particulate or the gas alone. Inhalation Inhalation of toxicants often constitutes the most rapid avenue of entry into the body because of the intimate association of air passages in the lungs with the circulatory system. On inhalation soluble gases tend to dissolve into the water surface of the pulmonary tract; insoluble gases generally penetrate to the alveolar level. Because the alveoli bring the blood into very close the direct proximity to air, gases may pass directly across the alveolar membrane and into the blood stream very efficiently. Particles when deposited on the alveoli, may dissolve and release their consistent compounds. Inhalation Particles when deposited on the alveoli, may dissolve and release their consistent compounds. The degree to which they enter the blood are circulated and delivered to the body’s tissues depends on the concentration inhaled, duration of exposure, solubility in blood and tissue, reactivity of the compound and the respiratory rate. Anything that decreases the partial pressure of oxygen in the alveoli reduces the oxygen available for exchange and thus deprives the body of oxygen. When the oxygen of the air is displaced by another gas, so that there is not enough to support life, or when a person is prevented from breathing it is called asphyxiation. Inhalation So, substances that dilute or displace the oxygen in air without any other effect are simple asphyxiants. Examples include: carbon dioxide, nitrous oxide, nitrogen or hydrocarbons. Compounds that block the transfer of oxygen to the tissues or the utilization of oxygen once it reaches the tissues are called chemical asphyxiants. Two most common examples are: CO and (carbon monoxide) and HCN (Hydrogen cyanide). Chemical agents that irritate the lungs may also impair oxygen uptake by other means. Irritant may inflame the respiratory tract, causing bronchitis or provoking an asthmatic attack or causing the lungs to be filled with fluid (pulmonary edema).