Introduction to Photochemical Smog ChemistryOzoneSlide 3Slide 4Slide 5Ozone Health EffectsLung function after exposure to O.32 ppm O3Athletic performanceHow do we measure OzoneSlide 10Slide 11Slide 12Slide 13Slide 14A calibration curveSlide 16Serial dilutions from stock solutionabsorbances are measured for each of the serially diluted standardsStandard CurveSlide 20We then compare our sample absorbance to the standard curveProblemsInstrumental techniques of measuring OzoneChemilumenescence measurement of OzoneUsing UV photometry to measure OzoneSlide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36In the urban setting there are a lot of ground base combustion sourcesSlide 38Slide 39Slide 40Slide 41Slide 42Slide 43Nitrogen Storage (warm vs. cool)Nitrogen Loss (HNO3 formation)Nitrogen Loss (alkylnitrates)Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52Slide 53Slide 54The Chamber had two sidesExample experiment with the following chamber concentrations:Solar Radiation ProfileExample MechanismPhotochemical SystemSlide 60Slide 61Slide 62Slide 63Slide 64Slide 65Slide 66How do we get mixing height in the morning?Mixing height in the morningSlide 69Slide 70Mixing height in the afternoonAfternoon Mixing heightSlide 73How do we get light into the mechanism??Light and rate constantsSlide 76Slide 77Slide 78Slide 79Slide 80Slide 81Slide 82Extending this kinetics approach to simulate secondary Aerosols formation by linking gas and particle phase chemistry An exploratory model for aerosol formation from biogenic hydrocarbons using a gas-particle partitioning/thermodynamic model-Kamens Research Group, ES&T, 1999 and 2001Slide 84Slide 85ObjectiveOverviewOH attack on a-pineneSlide 90Particle formation-self nucleationSlide 92Slide 93Overall Mechanism linked gas and particle phase rate expressionsSlide 95Slide 96Slide 97Introduction to Photochemical Smog ChemistryBasic Reactions that form O3Distinguish between O3 formation in the troposphere and stratosphereHow hydrocarbons and aldehydes participate in the formation of smog ozoneFormation of free radicalsNitrogen loss mechanismsSecondary aerosol formationRunning simple simulation modelsOzoneozone is a form of oxygen; it has three atoms of oxygen per moleculeIt is formed in the lower troposphere (the atmosphere we live up to 6 km) from the photolysis of NO2NO2 + light --> NO + O.O. + O2 -----> O3 (ozone)its concentration near the earth’s surface ranges from 0.01 to 0.5 ppmOzonebackground ranges from 0.02 to 0.06 ppmWhat is a ppm??A ppm in the gas phase is one molecule per 106 molecules air or1x10-6 m3 O3 per 1 m3 air or1x10-6 atmospheres per 1 atmosphere of airA ppm in water is 1x10-3grams /L waterOzonelet’s convert 1 ppm ozone to grams/m3 start with: 1x10-6 m3 per 1 m3 airwe need to convert the volume 1x10-6 m3 of O3 to gramslet’s 1st convert gas volume to moles and from the molecular weight convert to gramsat 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/molO3 has a MW of 48 g/moleso # g O3 in 1ppm = #moles Ox 48g/mole per m3= 4.1x10-5 g/m3Ozone Health EffectsOzone 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 air that enters the lungsSchool athletes perform worse under high ambient O3 concentrations, and asthmatics have difficulty breathingThe current US standard has been just reduced from 0.12 ppm for one hour to 0.08 ppm for one hourLung 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 Ozone40 years ago chemists borrowed techniques that were developed for water sampling and applied them to air samplingfor 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 Ozonea neutral buffered solution of potassium iodide is placed in a bubblerKI + O3 --> I2measure I2How do we measure OzoneAir 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 OzoneThe absorbance of the I2 in the KI solution is then measured with a spectrophotometerKI solution + I2How do we measure OzoneThe absorbance of the I2 in the KI solution is then measured with a spectrophotometerKI solution + I2How do we measure OzoneThe absorbance of the I2 in the KI solution is then measured with a spectrophotometerKI solution + I2SpectrophotometerA calibration curveA standard curve is constructed from known serial dilutions of I2 in KI solutionto do this I2 is weighed out on a 4 place balance and diluted with KI solution to a known volumeA calibration curveA standard curve is constructed from known serial dilutions of I2 in KI solutionto do this I2 is weighed out on a 4 place balance and diluted with KI solution to a known volumeI2Serial dilutions from stock solutionI25 3 2 1mg/Literabsorbances are measured for each of the serially diluted standardsSpectrophotometerabsorbanceStandard CurveI2 absorbances are plotted vs. concentration1 2 3 4 5 concentration (mg/liter)absorbanceHow do we measure OzoneThe absorbance of the I2 in the KI solution is then measured with a spectrophotometerKI solution + I2SpectrophotometerWe then compare our sample absorbance to the standard curveI2 absorbances are plotted vs. concentration1 2 3 4 5 concentration (mg/liter)absorbanceair sampleProblemsanything that will oxidize KI to I2 will give a false positive responseNO2, PAN, CH3-(C=O)-OO-NO2, give positive responsesSO2 gives a negative responseInstrumental techniques of measuring OzoneChemilumenescene became popular in the early 1970sFor ozone, it is reacted with ethyleneethylene forms a high energy state of formaldehyde, [H2C=O]*[H2C=O]*--> light + H2C=O A photomultiplyer tube measures the lightThe amount of light is proportional O3Chemilumenescence measurement of OzonePMtubepumpwaste ethylenecatalytic converterethyleneCO2 + H2OO3 sample air