2 the last event prompted the parliament to pass a Clean Air Act in 1956 HistoryMany of the worst air pollution episodes occurred in the last two centuries in Londonkey ingredientscalm windsfogsmoke from coal burningin deathsin deathsin over 4000 deaths;the last event prompted the parliament to pass a Clean Air Act in 1956
3 Other Eventsin Meuse Valley; pollution became trapped in a narrow valley people became ill, 63 were killedin 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 killedin 1960s - NYC experienced several dangerous episodesin 1960s and 70s - Los Angeles - increase in industry and automobile usage led to many pollution episodes
4 Grand Canyon on a good day 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 meetEven the most remote areas are affected by air pollution like the Grand CanyonGrand Canyon on a good dayThe Grand Canyon on a bad day
5 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 dustsuspended particlesvolcanic eruptionsdust, ash, gases like SO2, CO2forest firessmoke, ash, unburned hydrocarbons, CO2VegetationVOCs, pollenOcean Wavessalt particles
6 Anthroprogenic Sources industrypaper millspower plantsrefineriesmanufacturingparticulate matterSOxNOxAshpersonal:transportationhome furnacesfireplacesopen burning of refuseCOVOCsforest firessmoke, ash, unburned hydrocarbons, CO2
7 Primary Pollutants injected into the atmosphere directly carbon monoxide (CO)odorless, colorless, poisonous gascreated by incomplete combustion (especially bad with older cars)generates headaches,drowsiness, fatigue, can result in deathoxides of nitrogen (NOx, NO)NO - nitric oxideemitted directly by autos, industry
8 Primary Pollutants - 2 sulfur oxides (SOx) SO2 - sulfur dioxide produced largely through coal burningresponsible for acid rain problemvolatile organic compounds (VOCs)highly reactive organic compoundsrelease through incomplete combustion and industrial sourcesparticulate matter (dust, ash, salt particles)bad for lungs
9 Secondary Pollutantsform in the atmosphere through chemical and photochemical reactions from the primary pollutantssulfuric acid H2SO4can cause respiratory problemsnitrogen dioxide NO2gives air a brownish colorationozone O3colorless gas has a sweet smellis an oxidizing agent - lung tissue to rubber products irritates the eyes
10 How are the London and L.A.-type smogs produced ?????? PollutantsThe primary and secondary pollutants are found in either of the following two types of smog:London-type smogPhotochemical smog (produced in L.A. and many other urban areas around the world)How are the London and L.A.-type smogs produced ??????
11 Smog - smoke + fogLondon 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)
12 NOx + ROG + sunlight --> O3 + NO2 London vs. L.A. SmogLondon Smog: requires humid/foggy, stagnant airhave lots of coal burningSO2 + H20 -> H2SO4L.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 + NO2ROG are reactive organic gases from unburned gasolineNOx are oxides of nitrogen
13 London vs. L.A. Smog London smog: temperature inversion – the lower the betterhumid foggy, stagnant airair will look sooty, dirty, foggyLA smog:temperature inversion - the lower the betterhot sunny, stagnant weatherair looks hazy, brownish in color
14 Primary pollutants in LA smog CO - carbon monoxideNO - nitric oxideROG - 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
15 Secondary pollutants in LA smog O3 - ozoneNO2 - nitrogen dioxideParticlesPAN - peroxyacetyl nitrateThese are products of reactions in the atmosphere, NOT directly emittedThe main secondary pollutant is ozone, near the surface, up in the stratosphere, it's a good thing....
16 South Coast AQMD web site: http://www.aqmd.gov/smog/index.html 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:
17 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.
18 LA smog photochemistry – the null cycle A null cycle neither produces nor destroys anything overallso, how do ozone and nitrogen dioxide concentrations build up during the day ?????????something else is missing
19 Ozone Production - Null Cycle Observations of O3 concentration vs. time show that there is a significant increase in O3 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. . .
20 Reactive Organic Gasses Reactive organic gases (ROG) undergo a series of reactions to form radicalsThe alkylperoxy radical (RO2*) reacts with and oxidizes NO to form NO2 faster than NO reacts with O3 to produce the same resultThus, when ROGs are present, it is likely that O3 will not be destroyed to produce NO2, and the null cycle is brokenNote that each time an NO2 molecule is formed (by whatever method), it very quickly results in the production of O3 (via photo dissociation and a recombination)
22 NEW CYCLE WITH REACTIVE HYDROCARBONS THE NULL CYCLE WITH NO HYDROCARBONS
23 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 O3The greater the wind speeds and mixing heights the lower the smog concentrationIn addition, the direction of the windwill control the areas where smog istransported.
24 Geographical FactorsMountains 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)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.
25 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 afternoonWithout ROGs, the ozone concentration would remain low most of the dayAt night, there is no sunlight to photo dissociate NO2, so O3 is not produced. The O3 from the daytime photochemistry dissipates overnightTime series of ozone can be found at:for the LA Basin
26 Seasonal VariationsVariations in sunlight intensity cause variations in O3 production rateWhen the sun is most intense (i.e., Summer), O3 should reach highest levels, and primary pollutants should be at low concentrationsIn the winter, when the sun is weak, there will be reduced production of O3
27 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 intensityThe 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
29 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.The larger the volume, the lower the pollution concentration
30 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.
31 This gives the plume the appearance that it is looping around 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
32 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