Photochemical

After the industrial revolution, many factories are booming ever since. In the eagerness to cope with the modern phase, human tends to forget the adverse impacts caused by these increasing factories. Factories are the main source of air pollution. Air pollution consists of gases, liquids or solids present in the atmosphere in high level enough to harm humans, animals, plants and materials. Chemistry There are many air pollutants that exist as the result of human activities but according to Raven, Berg and Johnson (1995) there are only six main ones. This includes particulate nitrogen oxides, sulfur oxides, carbon oxides, hydrocarbons and ozone. Air pollutants can also be divided into two categories: primary and secondary. Primary air pollutants are harmful chemicals that enter directly into the atmosphere. The major ones arecarbon dioxides, nitrogen oxides, sulfure dioxide, particulate and hydrocarbons. Secondary air pollutants are harmful chemicals that form other substances that have been released into the atmosphere. Ozone and sulfure trioxide are secondary pollutants because both are formed by chemial reactions that take place in the atmosphere. The top three source of toxic air pollutants are the chemical industry, the metal industry and paper industry. Particulate matter consists of solid and liquid particles that are suspended in the atmosphere. Solid particulate matter is referred as dust whereas liquid suspensions are called mist. Particulate includes soil, soot, lead, asbestos and sulfuric acid droplets. Coarse dust particle, larger than micrometers in diameter, settles quickly and causes trouble only near their source. Smaller dust particles travel farther and are referred to as aerosols that remain suspended in the air for a long period of time. Aerosols reflect the sun’s heat and prevent it from reaching the Earth thus reducing visibility. Particle less than 2 or 3 micrometers in size can penetrate into the lungs that may result in respiratory diseases such as pneumonia, and chronic lung disease. Particle matter corrodes metals, erodes buildings and sculpture when the air is humid, and soil clothing and draperies. Nitrogen oxides are gases produced by chemical interactions between nitrogen and oxygen. They consist of nitric oxide (NO), nitrogen dioxide (NO2) and nitrous oxide (N2O). Nitrogen oxides inhibit plant growth and are involved in photochemical smog, acid deposition and global warming. Sulfur oxides are produced by sulfur and oxygen. Sulfur dioxide (SO2) is a colourless and non-flammable gas with a strong, irritating odor. When sulfur dioxide reacts with oxygen in the air, sulfur trioxide (SO3), a secondary pollutant is formed. Sulfur trioxide in turn reacts with water to form another secondary pollutant, sulfuric acid. Sulfur oxides form acid rain which corrodes metals and damage building structures. Sulfuric acid and sulfate salts damage plants and irritate the respiratory tract of animals and humans. Carbon oxides are gases such as carbon monoxide (CO) and carbon dioxide (CO2). Carbon monoxide, a colourless and tasteless gas is poisonous. It may reduce the blood’s ability a transport oxygen by combining with hemoglobin in the blood to form carboxyhemoglobin. Carbon monoxide can also cause dizziness, headaches, and slow driving reactions thus increase traffic accidents. Carbon dioxide is also colourless and odorless. It traps heat in the atmosphere which can cause global climate to change. Hydrocarbons are a diverse group of organic compounds that contain only hydrogen and carbon. Some hydrocarbons are straight or branched chains, and some are cyclic (form rings); the simplest form is methane (CH4). The smaller hydrocarbons are gaseous at room temperature; methane for example, is a colourless and odorless gas that is the principle component of natural gas. Medium-sized hydrocarbons are liquids at room temperature, although many are volatile, or evaporate easily. The largest hydrocarbons are in solid form in room temperature. All hydrocarbons are involbed in the production of photochemical smog except methane. Methane is involved in global climate change. Besides that, benzopyrene, the most potent hydrocarbon can cause lung cancer. Ozone (O3) is considered a pollutant in one part and an essential component in another. In the stratosphere, oxygen reacts with ultraviolet radiation from penetrating to the Earth’s surface. Unlike stratospheric ozone, tropospheric ozone is a human-made air pollutant. Tropospheric ozone is a secondary pollutant that forms when sunlight catalyzes a reaction between nitrogen oxides and hydrocarbons. Ozone damage plants and contribute to the forest decline and is also involved in global climate change. Social relevance Photochemical smog

Photochemical smog is a brownish haze formed by chemical reactions involving sunlight and is absorbed by nitrogen dioxide (NO2). The highly energised molecule (NO2*) then decomposes or photolyzes into nitrogen oxide (NO) and atomic oxygen (O). The latter reacts with molecular oxygen (O2) to form ozone (O3). If no energy-absorbing molecule (M) is present, the ozone will rapidly decompose. With a 3r4d body (M) present, a stable ozone molecule is formed. If nitric oxide is present, it reacts with the ozone to form more NO2 and a molecule of oxygen. These reactions are shown by the following chemical equations: NO2 + hv NO2* NO2* NO + O O + O2 + M O3 + M O3 + NO NO2 + O2 Some atomic oxygen, ozone and nitrogen can react with hydrocarbons to produce a variety of products such as peroxyacetyl nitrate (PAN). PAN is one of the photochemical smog’s most harmful component. There are also several negative impacts associated with photochemical smog. Photochemical smog can damage plant. A shiny, oily effect that appeared on the leaf’s lower surface developed into a glaze and turned silver is attributed to smog. Besides that, the cost of smog damage to vegetable production in the United States is approximately $10 million per year. Ozone could also damage the palisade layers of the top leaf and appears as flecking or stippling on broad leaves as streaks on the leaves of cereal crops, and as browning on the tip of pine needles. Flecking of tobacco leaves reduces their value particularly as cigar wrappers. Ozone has also caused the destruction of many acres of ponderosa pine in the San Bernadino Mountains. Whereas PAN iinjury appears as bronzing, silvering and glazing on lower leaf surfaces. Another subject that may be affected by photochemial smog is human. Formaldehyde acrolein, and PAN are the contributors to eye irritation. Ozone is a broncho-pulmonary irritant, which affects mucous lining of the lungs, which may lead to breathing problems such as bronchitis and emphysema. Annual deaths in the United States caused by photochemical smog is estimated to be 7000 – 180000. On top of that, this smog may also have an impact on materials. Ozone can cause cracking of stretched rubber. It can also attack the celulose in textiles, reducing the strength of such items. In addition, oxidants may cause fading of fabrics and polyster. Erosion of exterior painted surfaces due to attack on organic binder in the paint also occurs. The atmosphere has also been affected by photochemical smog. Visibility has in many cases been reduced prior to photochemical smog. In 1982, an incident once happen where MAS has to cancel all flights to due to the haze. Acid deposition Acid deposition is a type of air pollution that includes acid, which falls from the atmosphere to the Eath as precipitation or dry acidic particles. When sulfur and nitrogen oxides react with water, they form acids. This is called precipitation and it incldues acid rain, acid snow and acid fog. Dry deposition includes the direct updatake of gases such as SO2 and Nox by vegetation, soil and water surfaces plus the gravitational setting of particulate aerosols. Acid deposition has been proven to have adverse effects on plants, marine life, food chain, man-made structure and human. Global warming Carbon dioxide and certain other gases including methane (CH4), nitrous oxide (N2O), chloroflurocarbons (CFCs) and tropospheric ozone (O3) are accumulating in the atmosphere as th result of human activities. The concentration of atmospheric carbon dioxide has increased from about 280 parts per million approximately 200 years ago (before the Industrial Revolution began) to 360 per million today. Global warming occurs because these gasees prevent infrare radiation to dissipate into space from the Earth thus causing the atmosphere to warm. Some of the heat is also transferred to the ocean and raises their temperature as well. As the atmosphere and ocean warm, the overall temmperature of the Earth rises. Because carbon dioxide and other gases trap the sun’s radiation as glass does in a greenhouse, global warming produced in this manner is known as the greenhouse effect.