Presentation on theme: "AIR POLLUTION FUNDAMENTALS. History Many of the worst air pollution episodes occurred in the last two centuries in London key ingredients –calm winds."— Presentation transcript:
AIR POLLUTION FUNDAMENTALS
History Many of the worst air pollution episodes occurred in the last two centuries in London key ingredients –calm winds –fog –smoke from coal burning in deaths in deaths in over 4000 deaths; the last event prompted the parliament to pass a Clean Air Act in 1956
Other Events in Meuse Valley; pollution became trapped in a narrow valley people became ill, 63 were killed in the US, air quality degraded quickly shortly after the industrial revolution and again, the problem was coal burning in the central and mid western U.S. in Donora, PA in the Monongahela River Valley with a five-day episode 's became ill, 20 were killed in 1960s - NYC experienced several dangerous episodes in 1960s and 70s - Los Angeles - increase in industry and automobile usage led to many pollution episodes
Grand Canyon The above events led to passing the Clean Air Act of 1970 (updated in 1977 and again in 1990) empowered the federal government to set emission standards that each state would have to meet Even the most remote areas are affected by air pollution like the Grand Canyon Grand Canyon on a good day The Grand Canyon on a bad day
Pollutant Sources Air pollutants – airborne substances that occur in concentrations high enough to threaten the health of people and animals, to harm vegetation and structures, or to toxify a given environment (from Ahrens). Natural Sources: wind picking up dust suspended particles volcanic eruptions dust, ash, gases like SO 2, CO 2 forest fires smoke, ash, unburned hydrocarbons, CO 2 VegetationVOCs, pollen Ocean Wavessalt particles
Anthroprogenic Sources industry paper mills power plants refineries manufacturing particulate matter SOx NOx Ash personal: transportation home furnaces fireplaces open burning of refuse CO NOx VOCs particulate matter forest fires smoke, ash, unburned hydrocarbons, CO 2
Primary Pollutants injected into the atmosphere directly carbon monoxide (CO) –odorless, colorless, poisonous gas –created by incomplete combustion (especially bad with older cars) –generates headaches, drowsiness, fatigue, can result in death oxides of nitrogen (NOx, NO) –NO - nitric oxide –emitted directly by autos, industry
Primary Pollutants - 2 sulfur oxides (SOx) –SO2 - sulfur dioxide –produced largely through coal burning –responsible for acid rain problem volatile organic compounds (VOCs) –highly reactive organic compounds –release through incomplete combustion and industrial sources particulate matter (dust, ash, salt particles) –bad for lungs
Secondary Pollutants form in the atmosphere through chemical and photochemical reactions from the primary pollutants sulfuric acid H 2 SO 4 can cause respiratory problems nitrogen dioxide NO 2 gives air a brownish coloration ozone O 3 colorless gas has a sweet smell is an oxidizing agent - lung tissue to rubber products irritates the eyes
Pollutants The primary and secondary pollutants are found in either of the following two types of smog: London-type smog Photochemical smog (produced in L.A. and many other urban areas around the world) How are the London and L.A.-type smogs produced ??????
Smog - smoke + fog London Smog - This type of smog comes from coal smoke combining with the water vapor and liquid water in cool, humid or foggy air. L.A. smog has been identified as coming from auto exhaust, primarily (there is a significant "stationary" source)
London vs. L.A. Smog London Smog: requires humid/foggy, stagnant air have lots of coal burning SO 2 + H 2 0 -> H 2 SO 4 L.A. Smog:requires clear, sunny skies (since L.A. photochemical smog requires sunlight for at one of the key chemical reactions) NOx + ROG + sunlight --> O3 + NO2 ROG are reactive organic gases from unburned gasoline NOx are oxides of nitrogen
London vs. L.A. Smog London smog: temperature inversion – the lower the bettertemperature inversion humid foggy, stagnant air air will look sooty, dirty, foggy LA smog: temperature inversion - the lower the better hot sunny, stagnant weather air looks hazy, brownish in color
Primary pollutants in LA smog CO - carbon monoxide NO - nitric oxide ROG - reactive organic gases (unburned gasoline) These are mainly direct combustion products from gasoline- or diesel-burning internal combustion engines. There is a significant source of ROGs from stationary industries and small businesses
Secondary pollutants in LA smog O 3 - ozone NO 2 - nitrogen dioxide Particles PAN - peroxyacetyl nitrate These are products of reactions in the atmosphere, NOT directly emitted The main secondary pollutant is ozone, near the surface, up in the stratosphere, it's a good thing....
South Coast AQMD web site: Map of L.A. Basin area and air quality data: Real time air quality reading in the LA Basin area: Map archive of U.S. air quality: Another map showing NO2 and O3 concentrations with meteorological data as well can be found at:
Source of the Primary Pollutants - Photochemical Smog Mobile sources (such as automobiles) are the largest sources of CO to the atmosphere. Stationary industrial sources are the largest source of particulate matter (PM). ROGs seem to be shared between the stationary and mobile sources.
LA smog photochemistry – the null cycle A null cycle neither produces nor destroys anything overall so, how do ozone and nitrogen dioxide concentrations build up during the day ????????? something else is missing
Ozone Production - Null Cycle Observations of O 3 concentration vs. time show that there is a significant increase in O 3 during the afternoon. If the null cycle were the only process occurring in L.A. smog, then this observation would be anomalous. There must be something else...
Reactive Organic Gasses Reactive organic gases (ROG) undergo a series of reactions to form radicals The alkylperoxy radical (RO 2 *) reacts with and oxidizes NO to form NO 2 faster than NO reacts with O 3 to produce the same result Thus, when ROGs are present, it is likely that O 3 will not be destroyed to produce NO 2, and the null cycle is broken Note that each time an NO 2 molecule is formed (by whatever method), it very quickly results in the production of O 3 (via photo dissociation and a recombination)
NEW CYCLE WITH REACTIVE HYDROCARBONS THE NULL CYCLE WITH NO HYDROCARBONS
Factors affecting smog concentration Smog concentrations vary over time and space according to environmental conditions and sunlight (the source of energy for photochemical reactions) The higher the sunlight intensity, the greater production rate of O 3 The greater the wind speeds and mixing heights the lower the smog concentration In addition, the direction of the wind will control the areas where smog is transported.
Geographical Factors Mountains stop the horizontal transport of smog, or divert it in another direction, unless the wind is strong enough to blow over the mountain (not likely to happen in L.A., due to the inversion that prevents vertical mixing)due to the inversion that prevents vertical mixing) Since secondary pollution forms after the emission of primary pollution, we are likely to find the higher secondary pollution concentrations downwind of the source regions.
Diurnal Smog Variation Due to the time it takes for ozone to build up in the afternoon, the highest peaks of ozone occur inland, because the sea breeze transports pollutants inland during the afternoon Without ROGs, the ozone concentration would remain low most of the day At night, there is no sunlight to photo dissociate NO 2, so O 3 is not produced. The O 3 from the daytime photochemistry dissipates overnight Time series of ozone can be found at: for the LA Basin
Seasonal Variations Variations in sunlight intensity cause variations in O 3 production rate When the sun is most intense (i.e., Summer), O 3 should reach highest levels, and primary pollutants should be at low concentrations In the winter, when the sun is weak, there will be reduced production of O 3
Primary pollutants, such as CO, reach seasonal maxima during the winter, but more from the lower mixing heights during this season than from the reduced sunlight intensity The effect of low mixing heights would be to reduce the dispersion volume in which pollutants can mix, which increases the concentration if the source rate is the same
Air Pollution Dispersion Air pollution dispersion is often studied with simple models called box models. How is the box defined for the Los Angles area???? The ventilation factor gives us a way of relating the pollution concentration to the parameters that control dispersion of the pollution in the local environment. Basically, increasing either the mixing height or the wind speed increases the effective volume in which pollutants are allowed to mix.mixing height The larger the volume, the lower the pollution concentration
Chimney Plume Dispersion In the stable atmosphere case (producing a fanning plume), there is horizontal dispersion at a right angle to the wind due to turbulence and diffusion. In the vertical, dispersion is suppressed by the stability of the atmosphere, so pollution does not spread toward the ground. This results in very low pollution concentrations at the ground.
In unstable air, the plume will whip up and down as the atmosphere mixes around (whenever an air parcel goes up, there must be air going down someplace else to maintain continuity, and the plume follows these air currents). This gives the plume the appearance that it is looping around
An inversion aloft will trap pollutants underneath it, since the stable inversion prevents vertical dispersion. Pollution released underneath the inversion layer will fumigate the mixed layer. Note that if the smokestack was high enough to release the pollution within the inversion layer, the plume would fan because the plume occurs within stable air