External Air Pollution - Particulate Pollutants (Smoke & Fumes)   External air pollution comes from airborne particulate matter, which is a complex and varying mixture of substances. Particulates include dust, dirt, smoke, soot, bits of metal and silica etc. Sources include motor-vehicle emissions, factory and utility smokestacks, residential wood burning, construction activity, mining, agricultural tilling, open burning, wind-blown dust, and fire.   Some particles are formed in the atmosphere through the condensation or transformation of other chemical substances. Particles with diameters less than 10µm pose a greater health risk than larger particles because they can be easily inhaled deep into the lung.   The levels of outdoor air pollutants depend on a number of factors, including local production, sunlight, and the prevailing winds. A high pressure weather system, which is characterized by fine, hot weather with clear skies and little or no wind, will increase the likelihood of pollution-ladden fog, or "smog".   Major Gaseous Pollutants in Outdoor Air The major outdoor air pollutants encountered by allergy sufferers are derived form burning fossil fuels - in particular, sulphur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), acid aerosols, and ozone (O3). Exposures to SO2, NO2, and O3 have all been shown to worsen asthma and rhinitis as well as contributing to respiratory infections and conjunctival diseases. Severe rhinitis may follow exposure to smoke and fumes from commercial and industrial activities. Particulate air pollution not only has acute effects on the respiratory system by also worsen the conditions of chronic respiratory diseases.   1. Sulphur Dioxide (SO2) – People prone to allergy, especially those with allergic asthma, can be very sensitive to inhaled sulphur dioxide. Symptoms may include bronchospasm, hives, gastro-intestinal disorders, and inflammation of the walls of the blood vessels (vasculitis-related disorder)..   Note: Sulphur dioxide is a colourless gas that readily dissolves in water to form sulphuric acid (H2SO4), which then falls as acid rain.   2. Nitrogen Dioxide (NO2) – Temporary or perhaps permanent bronchial hypersensitivity has been connected to inhaling nitrogen dioxide. Long-term exposure to nitrogen dioxide has been associated with the increased occurrence of respiratory diseases.   Note: Nitrogen dioxide is a strong oxidant. It is generated naturally by bacteria, volcanic action and by lightning. In modern cities, high levels of NO2 are due to the burning of fossil fuels in power plants, factories and cars.   3. Carbon monoxide (CO) – It is an odorless, colorless gas that can cause sudden illness and death.   Note: Carbon monoxide is found in combustion fumes, such as those produced by cars and trucks, small gasoline engines, stoves, lanterns, burning charcoal and wood, and gas ranges and heating systems. CO from these sources can build up in enclosed or semi-enclosed spaces. People and animals in these spaces can be poisoned by breathing it.   4. Acid aerosol – The major chemicals in acid aerosols include sulphuric acid, hydrochloric acid and hydrofluoric acid. Acid aerosols include mists, vapors, gas, fog, and other airborne forms of any particle size of these acids. They are formed during combustion.   Note: Hydrochloric acid aerosols and hydrogen fluoride form during the combustion of fuels/wastes containing chlorine and fluorine.   Sulphuric acid aerosols form in stacks from combustion processes of fuel oil, coal, and other sulphur-containing fuels. Sulphur trioxide, a product of fuel combustion, can react quickly to form sulphuric acid in the presence of moisture.   5. Ozone (O3) - Temporary or perhaps permanent bronchial hypersensitivity has been connected to inhaling ozone.   Note: Ozone is a powerful oxidizing agent. It is a secondary pollutant created when sunlight reacts with vehicle exhaust products (NO2) in the presence of hydrocarbons. Hence, ozone is termed a photo chemical pollutant.     Related Link: Living in Dirty Air Increases Fatal Heart Attacks and Non-fatal Ones