EnE 301: ENVIRONMENTAL ENGINEERING

1. EnE 301: ENVIRONMENTAL ENGINEERING • 3.1 Physical and Chemical Fundamentals • 3.2 Major Air Pollutants and their Effects • 3.3 Origin and Fate of Air Pollutants • 3.4 Micro and Macro Air Pollution and Meteorology • 3.5 Atmospheric Dispersion and Air Quality Model • 3.6 Air Pollution Control of Stationary and Mobile • Sources • 3.7 Clean Air Act of 1999- RA8749 and Its Implementing • Rules and Regulations 3.0 Air Pollution and Control

2. Carbon Monoxide • Incomplete oxidation of carbon results in the production of carbon monoxide. • The natural anaerobic decomposition of carbonaceous material by soil microorganisms releases approximately 9 x 1015 moles of methane (CH4) to the atmosphere each year worldwide. The natural formation of CO results from an intermediate step in the oxidation of the methane. • Anthropogenic sources (those associated with the activities of human beings) include motor vehicles, fossil fuel burning for electricity and heat, industrial processes, solid waste disposal, and miscellaneous burning of such things as leaves and brush. Approximately 1 x 1013 moles of CO are released by these sources. Motor vehicles account for more than 60 percent of the emission. • Mechanisms to account for the missing CO include: (1) Reaction with hydroxyl radicals to form carbon dioxide (2) Removal by soil microorganisms. Origin and Fate of Pollutants

3. Hazardous Air Pollutants • The source categories include fuel combustion, metal processing, petroleum and natural gas production and refining, waste treatment and disposal processes, agricultural chemicals production, polymers and resin production, dry cleaning and electroplating. • The major removal mechanisms appear to be the hydroxyl radicals (OH) abstraction or addition. The reaction products lead to the formation of CO and CO2. Lead • Volcanic activity and airborne soil are the primary natural sources of atmospheric lead. • Smelters and refining processes, as well as incineration of lead-containing wastes, are major point sources of lead. • Approximately 70 to 80 percent of the lead added to gasoline is discharged to the atmosphere. • Lead particles, which are formed by volatilization and subsequent condensation, attach to larger particles or form nuclei before being removed from the atmosphere.

4. Nitrogen Dioxide • Bacterial action in the soil releases nitrous oxide (N2O) to the atmosphere. In the upper troposphere and stratosphere, atomic oxygen reacts with the nitrous oxide to form nitric oxide (NO). N2O + O –> 2NO • The atomic oxygen results from the dissociation of ozone. The nitric oxide further reacts with ozone to form nitrogen dioxide (NO2). NO + O3 –> NO2 + O2 • Combustion processes account for 96% of the anthropogenic sources of nitrogen oxides. Although nitrogen and oxygen coexist in our atmosphere without reaction, their relationship is much less indifferent at high temperatures and pressures. At temperatures in excess of 1,600 K, they react. N2 + O2 –> 2NO • The NO in turn reacts with ozone or oxygen to form NO2. Ultimately, the NO2 is converted to either NO2 or NO3 in particulate form. The particulates are then washed out by precipitation. • The dissolution of nitrate in a water droplet allows for the formation of nitric acid (HNO3). This, in part, accounts for “acid” rain found downwind of industrialized areas.

5. Photochemical Oxidants • They are called secondary pollutants, which are formed through a series of reactions that are initiated by the absorption of a photon by an atom, molecule, free radical, or ion. • Ozone is the principal photochemical oxidant. Its formation is usually attributed to the nitrogen dioxide photolytic cycle. • Hydrocarbons modify this cycle by reacting with atomic oxygen to form free radicals. The hydrocarbons, nitrogen oxides, and ozone react and interact to produce more nitrogen dioxide and ozone. • A result of these reactions is the photochemical “smog”. Sulfur Oxides • Sulfur oxides may be both primary and secondary pollutants. Power plants, industry, volcanoes, and the oceans emit SO2, SO3 and SO4 directly as primary pollutants. • In addition, biological decay processes and some industrial sources emit H2S, oxidized to form the secondary pollutant SO2. • The most important oxidizing ration for H2S appears to be one involving ozone: H2S + O3 –> H2O + SO2

6. The combustion of fossil fuel containing sulfur yields sulfur dioxide in direct proportion to the sulfur content of the fuel: S + O2 –> SO2 • The reaction implies that for every gram of sulfur in the fuel, two grams of SO2 are emitted to the atmosphere. • In general, we assume that 5% of sulfur in fuel ends up in the ash. • The ultimate fate of most of the SO2 in the atmosphere is conversion to sulfate salts, which are removed by sedimentation or by washout with precipitation. Example No. 4:An Illinois coal is burned at a rate of 1.0 kg per second. If the analysis of the coal reveals a sulfur content of 3%, what is the annual rate of emission of SO2 in kg/yr? Particulates • Sea salt, soil dust, volcanic particles, and smoke from forest fires account for 1.404 Pg of particulate emissions each year. • Anthropogenic emissions from fossil fuel burning and industrial processes account for emissions of 92 Tg per year.

7. Secondary sources of particulates include the conversion of H2S, SO2, NOx, NH3, and hydrocarbons. • H2S and SO2 are converted to sulfates. • NOx and NH3 are converted to nitrates. • The hydrocarbons react to form products that condense to form particles at atmospheric temperatures. • Dust particles that are entrained by the wind and carried over long distances tend to sort themselves out to the sizes between 0.5 and 0.5 mm in diameter. • Sea salt nuclei have sizes between 0.05 and 0.5 um. • Particles formed as a result of photochemical reactions tend to have very small diameter (<0.4 mm). • Smoke and fly ash particles cover a wide range of sizes from 0.05 to 200 mm or more. • Small particles are removed from the atmosphere by accretion to water droplets, which grow in size until they are large enough to precipitate. • Larger particles are removed by direct washout by falling raindrops.

8. Volatile Organic Compounds • Volatile organic compounds or VOCs are organic chemicals that have a high vapor pressure at ordinary room-temperature conditions. • Their high vapor pressure results from a low boiling point, which causes large numbers of molecules to evaporate or sublimate from the liquid or solid form of the compound and enter the surrounding air. Sources: Paints and Coatings A major source of man-made VOCs are coatings, especially paints and protective coatings. Solvents are required to spread a protective or decorative film. Approximately 12 billion litres of paints are produced annually. Typical solvents are aliphatic hydrocarbons, ethyl acetate, glycol ethers, and acetone. Motivated by cost, environmental concerns, and regulation, the paint and coating industries are increasingly shifting toward aqueous solvents.

9. Chlorofluorocarbons Chlorofluorocarbons, which are banned or highly regulated, were widely used cleaning products and refrigerants. Tetrachloroethene is used widely in dry cleaning and by industry. Industrial use of fossil fuels produces VOCs either directly as products (e.g., gasoline) or indirectly as by-products (e.g., automobile exhaust). Benzene One VOC that is a known human carcinogen is benzene, which is a chemical found in environmental tobacco smoke, stored fuels, and exhaust from cars. Benzene also has natural sources such as volcanoes and forest fires. It is frequently used to make other chemicals in the production of plastics, resins, and synthetic fibers. Benzene evaporates into the air quickly and the vapor of benzene is heavier than air allowing the compound to sink into low-lying areas. Benzene has also been known to contaminate food and water and if digested can lead to vomiting, dizziness, sleepiness, rapid heartbeat, and at high levels, even death may occur.

10. Methylene Chloride Methylene chloride is another VOC that is highly dangerous to human health. It can be found in adhesive removers and aerosol spray paints and the chemical has been proven to cause cancer in animals. In the human body, methylene chloride is converted to carbon monoxide and a person will suffer the same symptoms as exposure to carbon monoxide. If a product that contains methylene chloride needs to be used the best way to protect human health is to use the product outdoors. If it must be used indoors, proper ventilation is essential to keeping exposure levels down. Perchloroethylene Perchloroethylene is a volatile organic compound that has been linked to causing cancer in animals. It is also suspected to cause many of the breathing related symptoms of exposure to VOC’s. Perchloroethylene is used mostly in dry cleaning. Studies show that people breathe in low levels of this VOC in homes where dry-cleaned clothes are stored and while wearing dry-cleaned clothing.

11. Air Pollution Scales • Micro-scale problems range from those covering a centimeter to the size of a house or slightly larger. • Meso-scale air pollution problems are those of a few hectares up to the size of a city or country (i.e. acid rain). • Macro-scale problems extend from countries to states, nations, and the globe (i.e. ozone depletion, greenhouse effect) . • Carbon monoxide from improperly operating furnaces has long been a serious concern. In numerous instances, people have died from furnace malfunction. • More recently, chronic low levels of CO pollution have been recognized. • Gas ranges, ovens, pilot lights, gas and kerosene space heaters, and cigarette smoke all contribute. • Indoor tobacco smoking is of particular concern because of the increasing evidence of the carcinogenic properties of the smoke. • While mainstream smoking (taking a puff) exposes the smoker to large quantities of toxic compounds, the smoldering cigarette in the ashtray (side stream smoke) also adds a considerable burden to the room environment.

12. The atmosphere is somewhat like an engine. It is continually expanding and compressing gases, exchanging heat, and generally raising chaos. • The driving energy for this unwieldy machine comes from the sun. • The difference in the heat input between the equator and the poles provides the initial overall circulation of the earth’s atmosphere. • The rotation of the earth coupled with the different heat conductivities of the oceans and land produce weather. Air Pollution Meteorology High and Low Pressures • Because air has mass, it also exerts pressure on things under it. • Like water, which we intuitively understand to exert greater pressure at greater depths, the atmosphere exerts more pressure at the surface than it does at higher elevations. • The elliptical lines shown on more detailed weather maps are lines of constant pressure, or isobars.

13. The wind flows from the higher pressure areas to the lower pressure areas. • On a non-rotating planet, the wind direction would be perpendicular to the isobars. • However, since the earth rotates, an angular thrust called the Coriolis effect is added to this motion. • The technical names given to these systems are anticyclones for highs and cyclones for lows. • Anticyclones are associated with good weather. Cyclones are associated with foul weather. • Tornadoes and hurricanes are the foulest of the cyclones. • Wind speed is in part a function of the steepness of the pressure surface. • When the isobars are close together, the pressure gradient (slope) is said to be steep and the wind speed relatively high. • If the isobars are well spread out, the winds are light or nonexistent.

14. Turbulence (1) Mechanical Turbulence • Turbulence is the addition of random fluctuations of wind velocity to the overall average wind velocity. • The shearing results from the fact that the wind speed is zero at the ground surface and rises with elevation to near the speed imposed by the pressure gradient. • The greater the mean wind speed, the greater the mechanical turbulence. • The more mechanical turbulence, the easier it is to disperse and spread atmospheric pollutants. (2) Thermal Turbulence • Heating of the ground surface causes turbulence in the same fashion that heating the bottom of a beaker full of water causes turbulence. • Likewise, if the earth’s surface is heated strongly and in turn heats the air above it, thermal turbulence will be generated.

15. Stability • The tendency of the atmosphere to resist or enhance vertical motion is termed stability. • There are three stability categories. • When the atmosphere is classified as unstable, mechanical turbulence is enhanced by the thermal structure. • A neutral atmosphere is one in which the thermal structure neither enhances nor resists mechanical turbulence. • When the thermal structure inhibits mechanical turbulence, the atmosphere is said to be stable. • Cyclones are associated with unstable air while anticyclones are associated with stable air. (1) Neutral Stability • The lapse rate for a neutral atmosphere is defined by the rate of temperature increase (or decrease) experienced by a parcel of air that expands (or contracts) adiabatically (without the addition or loss of heat) as it is raised through the atmosphere.

16. This rate of temperature decreases (dT/dz) is called the dry adiabatic lapse rate. It is designated by the Greek letter gamma (G) and has a value of approximately -1.00oC/100m. (2) Unstable Atmosphere • If the temperature of the atmosphere falls at a rate greater than G (for example, -1.01oC/100m), the lapse rate is said to be super-adiabatic, and the temperature is unstable. • If we capture a balloon full of polluted air at elevation A and adiabatically displace it 100m vertically to elevation B, the temperature of the air inside the balloon will decrease from 21.15 to 20.15C. • At a lapse rate of -1.25oC/100m, the temperature of the air outside the balloon will decrease from 21.15 to 19.90C. • The air inside the balloon will be warmer than the air outside, thus giving the balloon a buoyancy.

17. (3) Stable Atmosphere • If the temperature of the atmosphere falls at a rate less than G (for example, -0.99oC/100m), it is called sub-adiabatic lapse rate, and the atmosphere is stable. • Isothermal lapse rate- when there is no change of temperature with elevation. • Inversion lapse rate- when the temperature increases with elevation. Example No. 5:Given the following temperature and elevation data, determine the stability of the atmosphere and type of lapse rate. Elevation (m) Temperature (oC) 2.00 14.35 324.00 11.13

18. Seatwork No. 6:Determine the atmospheric stability (neutral, unstable, stable) and the lapse rate (adiabatic, super-adiabatic, sub-adiabatic, isothermal, inversion) of the following temperature profiles. Show all computations. Express all lapse rates in oC/100m (retain at least two decimal places in your final answers, i.e., -1.35 oC/100m). Elevation (m) Temperature (oC) a) 1.5 -4.49 349.0 0.10 b) 12.0 28.05 279.0 19.67 c) 8.0 18.55 339.0 17.93