Urban Atmospheric Pollution

Urban Atmospheric Pollution • Air Pollution • Pollutants • Health Effects • The Geography of Los Angeles Air Pollution • Mountain Barriers • Inversion Layers • Pollution Levels and Trends • Urban Heat Islands • Acid Rain (Acid Deposition) Air Pollutants Defining Dirty Air • Smog is the general term used to describe a variety of air pollutants, including ground-level ozone (smog's main ingredient), particulate matter, carbon monoxide and nitrogen oxides. It refers to air pollution that is formed when gases from many sources are released into the air and chemically react with each other in sunlight. Ocean breezes sweep the smog inland toward the mountains where an inversion layer of warm air pushes it down, trapping the smog close to the ground where we live and breathe. • Ground-level ozone (O3) is a colorless, odorless pollutant formed by a chemical reaction between volatile organic compounds (VOCs) and oxides of nitrogen (NOx) in the presence of sunlight. The primary source of VOCs and NOx is mobile sources, including cars, trucks, buses, plus agricultural and construction equipment. In contrast, stratospheric ozone in our upper atmosphere, better known as the ozone layer, shields the earth from the sun’s harmful ultraviolet rays. Particulate matter (PM) is the term used for a mixture of solid particles and liquid droplets found in the air. It originates from a variety of sources, including motor vehicles, power plants, construction activities, soil dust, soot and industrial processes. Coarse particles (PM10) are generally emitted from sources such as windblown dust, vehicles traveling on unpaved roads, and crushing and grinding operations. Fine particles (PM2.5) can come from fuel combustion (motor vehicles, power generation, industrial facilities) and fugitive dust. PM2.5 is formed primarily in the atmosphere from gases such as sulfur oxides, NOx, and VOCs. Carbon monoxide (CO) is a colorless, odorless gas by-product of combustion produced primarily by motor vehicles. Burned wood and charcoal also emit carbon monoxide. Ground-level Ozone • Ozone is a strong irritant that can constrict the airways, forcing the respiratory system to work harder to provide oxygen. It also can cause: • Aggravated respiratory diseases such as emphysema, bronchitis and asthma • Damage to deep portions of the lungs, even after symptoms such as coughing or a sore throat disappear • Wheezing, chest pain, dry throat, headache, or nausea • Reduced resistance to infection and increased fatigue Particulate Matter • A series of scientific studies have linked particulate matter, especially fine particles, with a variety of significant health problems: • Aggravated asthma, heart, or lung disease • Respiratory-related hospital admissions and emergency room visits • Acute respiratory symptoms, including severe chest pain, gasping, and aggravated coughing • Decreased lung function which can be experienced as shortness of breath • Chronic bronchitis • Premature death Carbon Monoxide • Carbon monoxide replaces oxygen in the body's red blood cells. People with heart disease are more susceptible to developing chest pains when exposed to low levels of carbon monoxide. Exposure to high levels of carbon monoxide can: • Slow reflexes and cause confusion and drowsiness • Result in death in confined spaces (i.e., an enclosed garage) at very high concentrations Current Los Angeles Smog Conditions: http://www.aqmd.gov/smog/areamap.html How to Control Los Angeles Smog? Since smog was first recognized as a serious problem in 1947, inventors and engineers have proposed innovative ideas to get rid of it. • One was to connect all Los Angeles industries to a massive network of concrete exhaust pipes routed to the mountains where pollution could be released above the inversion layer. If it works for sewage, it will work for air pollution, thought the engineering firm that pioneered the "air sanitation system" concept. But the system would have required 89 miles of ductwork and the energy to move the large volumes of air would have been several times beyond what Hoover Dam could supply. Many other ideas surfaced in the 1950s and 1960s to purify, ventilate or wash the air over Los Angeles. • One was to cut holes in the mountains and install huge exhaust fans to blow smog out of the basin. However, blowing or washing away smog proved to be impractical since it involved a land mass of 1,600 square miles and over 200 million tons of air. The enormous energy requirements made the idea impossible. • One scientist suggested blackening whole sections of the eastern mountains so as to store heat and create thermal currents and westerly winds that would blow smog over the mountains How to Control Los Angeles Smog? • 1970 Clean Air Act (amended repeatedly until 1990) sets standards for 6 key pollutants. States then implement plans to comply. Criteria Pollutant Sulfur dioxide Major Sources 65% from power plants; produced by combustion of sulfur-bearing fuels (e.g., coal, oil) and smelter ore Health Impacts and Environmental Damage Causes asthma attacks at high concentrations; Causes acid rain Other Important Considerations Precursor to particulate matter Nitrogen dioxide 29% as a combustion Damages soil and water bodies due product from power plants to eutrophication and nitrogen saturation; Causes acid rain At ground level, formed when NOx reacts with volatile organic compounds in the presence of sunlight Precursor to ground-level ozone and fine particulate matter Ozone Strong lung irritant, associated with Main component of "photochemical smog" decreases in lung function, lung tissue damage, chronic lung and heart diseases; Damages crops and forests; Causes regional haze conditions, damaging visibility in national parks Like ground-level ozone, PM can cause damage hundreds or thousands of miles beyond point of emission, due to longrange transport on prevailing wind and weather patterns Largely a problem of central city areas Particulate matter (PM) Emitted directly by Power Strongly associated with chronic lung plants, and formed in and heart disease; atmosphere from sulfur and nitrogen oxide emissions Carbon monoxide Released principally by cars and trucks Deadly at high concentrations; Displaces oxygen in blood at levels found in many urban centers Lead Emitted by lead smelters Neurotoxin, deadly in high doses; and garbage incinerators, Impairs brain development in and, in trace amounts, children; Inhibits proper development during coal combustion of fetuses Total lead emissions dropped 96% from 1970 to 1987due to elimination of leaded gasoline How to Control Los Angeles Smog? • 1970 Clean Air Act (amended repeatedly until 1990) sets standards for 6 key pollutants. States then implement plans to comply. • Key elements in California have been automobile smog checks, more refined gasoline required statewide, smokestack scrubbers which catch particulate and oxides of nitrogen and sulfer. • New management plans call for increased use of cleaner solvents that release fewer volatile organic compounds (VOCs). Dry cleaning, manufacturing, etc.. • Scrubbers use lime or ammonica to remove NOx and SOx • Catalytic converters on automobiles remove NO x Historic Smog Levels, Los Angeles Causes: • heat generating factories, cars, air conditioners • large areas of paved streets (dark, low specific heat) • few trees (less evaporation and water storage) • dark roofs Urban Heat Island Effects Urban Heat Islands Contribute: Smog: photochemical Reactions Increase with Temperature Changed microclimate: warmer, rainier, foggier, cloudier Urban Heat Island Effects Urban Heat Island Effects Acid Deposition What causes acid rain? Acid rain is rain, snow or fog that is polluted by acid in the atmosphere and damages the environment. Two common air pollutants acidify rain: sulphur dioxide (SO2) and nitrogen oxide (NOX). When these substances are released into the atmosphere, they can be carried over long distances by prevailing winds before returning to earth as acidic rain, snow, fog or dust. When the environment cannot neutralize the acid being deposited, damage occurs. Effects of Acid Deposition Death of fish Death of fish is the best known effect of acidification, and is therefore a reliable and frequently used indicator. There are two reasons for the death of fish. When the acidification reaches a certain level, the fry die. Different species of fish have different tolerance levels to acidic water. The most sensitive species are trout and salmon. See Table III.6 in Goudie and Viles Damage to vegetation Damage to vegetation and the dying of forests have long been associated with acid rain. The washing out of metal ions results in limited plant nutrients. (Nitrogen, Phosphorus, Potassium, Magnesium etc) In many cases, a plant’s ability to absorb these nutrients depends on the level of acidification in the soil. Vegetation exposed to acid rain will therefore absorb less of these essential nutrients. The result is poorer quality of a plant’s proteins, stunted growth and exposure to diseases. See Figure III.6 in Goudie and Viles Acid Depostion Sources of sulfer oxides (SOx) Sources of nitrogen oxides (NOx)