Introduction to Photochemical Smog ChemistryWhy are we interested in the Smog Chemistry???OzoneSlide 4Slide 5Slide 6Ozone Health EffectsLung function before exposure to O.32 ppm O3Lung function after exposure to O.32 ppm O3Athletic performanceHow do we measure OzoneSlide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19A calibration curveSlide 21Serial dilutions from stock solutionSlide 23Slide 24Slide 25Slide 26absorbances are measured for each of the serially diluted standardsMaking a plotWe then compare our sample absorbance to the standard curveProblemsInstrumental techniques of measuring OzoneChemilumenescence measurement of OzoneUsing UV photometry to measure OzonePowerPoint PresentationSlide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44In the urban setting there are a lot of ground base combustion sourcesSlide 46Slide 47Slide 48Slide 49What if NO is very low; the primary reaction is with HO2 Jenkin et al, 1997 Atmos. Envir., Pitts and Pitts , 186What are the reactions of RO2 (self reactions)?Is there data on the branching of 2RO vs. ROH+RCHO??Reactions or RO2 with NOFraction of Organic Nitrate from RO2. +NO Pitts and Pitts Table 6.5, p186The molecule can fall apart (page 189 Pitts and Pitts)We get RO. from two general reactions. What happens to these alkoxy radicals (RO.)?Slide 57Slide 58Nitrogen Storage (warm vs. cool)Where do we get rate coefficeints for the formation of PAN and the decompostion for PAN??The role of XO2 in CB4 type mechanismsNitrogen Loss (HNO3 formation)Nitrogen Loss (alkylnitrates)Slide 64Slide 65Slide 66Slide 67Slide 68Slide 69Slide 70Slide 71The Chamber had two sidesExample experiment with the following chamber concentrations:Solar Radiation ProfileExample MechanismPhotochemical SystemSlide 77How do we get light into the mechanism??Light and rate constantsSlide 80Slide 81Slide 82Slide 83Slide 84Slide 85Solar flux striking the earthSlide 87Light and rate constants (zenith angle)Slide 89Slide 90Slide 91Slide 92Slide 93Introduction to Photochemical Smog ChemistryBasic Reactions that form O3Distinguish between O3 formation in the troposphere and stratosphereHow hydrocarbons and aldehydes participate in the formation of smog ozoneFormation of free radicalsNitrogen loss mechanismsRunning simple simulation modelsWhy are we interested in the Smog Chemistry???Ozoneozone is a form of oxygen; it has three atoms of oxygen per moleculeIt is formed in the lower troposphere (the atmosphere we live up to 6 km) from the photolysis of NO2NO2 + light --> NO + O.O. + O2 -----> O3 (ozone)its concentration near the earth’s surface ranges from 0.01 to 0.5 ppmOzonebackground ranges from 0.02 to 0.06 ppmWhat is a ppm??A ppm in the gas phase is one molecule per 106 molecules air or1x10-6 m3 O3 per 1 m3 air or1x10-6 atmospheres per 1 atmosphere of airA ppm in water is 1x10-3grams /L waterOzonelet’s convert 1 ppm ozone to grams/m3 start with: 1x10-6 m3 per 1 m3 airwe need to convert the volume 1x10-6 m3 of O3 to gramslet’s 1st convert gas volume to moles and from the molecular weight convert to gramsat 25oC or 298K one mole of a gas= 24.45liters or 24.45x10-3 m3Ozone we have 1x10-6 m3 of ozone in one ppm so: 1x10-6 m3 --------------------- = #moles O324.45x10-3 m3/molO3 has a MW of 48 g/moleso # g O3 in 1ppm = #moles Ox 48g/mole per m3= 4.1x10-5 g/m3Ozone Health EffectsOzone causes dryness in the throat, irritates the eyes, and can predispose the lungs to bacterial infection.It has been shown to reduce the volume or the capacity of the lungs for air School athletes perform worse under high ambient O3 concentrations, and asthmatics have difficulty breathingThe current US standard has been just reduced from 0.12 ppm for one hour to 0.075 ppm for 8 hours.Lung function before exposure to O.32 ppm O30 2 4 6 8 Liters/sec0 1 2 3 4 LitersbeforeLung function after exposure to O.32 ppm O30 2 4 6 8 Liters/sec0 1 2 3 4 Litersbefore afterAthletic performance0 10 20 30 40 50 60 70 80 d e c re a se d p e rfo rm a n c e %0.1 0.15 0.2 0.25 0.3 0.35 0.4 O3 in ppm1962-19641959-1961How do we measure Ozone40 years ago chemists borrowed techniques that were developed for water sampling and applied them to air samplingfor oxidants, of which O3 is the highest portion, a technique called “neutral buffered KI was used.a neutral buffered solution of potassium iodide was placed in a bubblerHow do we measure Ozonea neutral buffered solution of potassium iodide is placed in a bubblerKI + O3 --> I2measure I2How do we measure Ozonea neutral buffered solution of potassium iodide is placed in a bubblerKI + O3 --> I2measure I2KI solutionHow do we measure OzoneA top is added to the bubbler so that air can enter the KI solutionKI + O3 --> I2measure I2KI solutionHow do we measure Ozonea pump is attached to the bubblerKI solutionpumpHow do we measure OzoneAir goes in through the top of the bubbler and oxidants are trapped in the KI liquid and form I2Air goes inKI solution + I2How do we measure OzoneThe absorbance of the I2 in the KI solution is then measured with a spectrophotometerKI solution + I2How do we measure OzoneThe absorbance of the I2 in the KI solution is then measured with a spectrophotometerKI solution + I2How do we measure OzoneThe absorbance of the I2 in the KI solution is then measured with a spectrophotometerKI solution + I2SpectrophotometerA calibration curveA standard curve is constructed from known serial dilutions of I2 in KI solutionto do this I2 is weighed out on a 4 place balance and diluted with KI solution to a known volumeA calibration curveA standard curve is constructed from known serial dilutions of I2 in KI solutionto do this I2 is weighed out on a 4 place balance and diluted with KI solution to a known volumeI2Serial dilutions from stock solutionI2Serial dilutions from stock solutionI25mg/LiterSerial dilutions from stock solutionI25 3mg/LiterSerial dilutions from stock solutionI25 3 2mg/LiterSerial dilutions from stock solutionI25 3 2 1mg/Literabsorbances are measured for each of the serially diluted standardsSpectrophotometerabsorbanceMaking a plotI2 adsorbances are plotted vs. concentrationWe then compare our sample absorbance to the standard curveI2 absorbances are plotted vs. concentration1 2 3 4 5 concentration (mg/liter)absorbanceair
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