Presentation on theme: "Nitrogen Oxides Pollution"— Presentation transcript:
1 Ultraviolet-Visible Spectroscopy in the Detection of Nitrogen Oxide Air Pollutants
2 Nitrogen Oxides Pollution NOx forms from emissions from vehicles, power plants, and off-road equipmentAdverse Effects:Formation of ground level ozone in the presence of heat of sunlightAirway inflammation and increased respiratory symptoms in asthma patientsNitrogen DioxideChildren, the elderly, people with lung diseases such as asthma, and people who work or exercise outside are at risk for adverse effects from ozone. These include reduction in lung function and increased respiratory symptoms as well as respiratory-related emergency department visits, hospital admissions, and possibly premature deaths.Ozone
3 EPA RegulationEPA sets national standard for nitrogen oxide ambient air concentrations to 53 ppb (annual average)Decreased by more than 40% since 1980Expected to decrease further as mobile source regulations that are taking effectUltraviolet-visible (UV-Vis) spectroscopy can determine the concentration of nitrogen oxides.
4 Ultraviolet-Visible Spectroscopy Molecular absorption due to excitation of bonding electronsCan identify functional groupsCan quantify compounds with absorbing groupsThe lowest energy transition is the HOMO-LUMO gap in the ground state (DE).If energy of light exactly matches DE, photon can be absorbedMore conjugated systems have smaller HOMO-LUMO gapHave lower DE and absorb longer wavelength of light
5 UV-Vis measurements Sample dissolved into a non-absorbing solvent Sample placed in cellA cell of pure solvent is also analyzed as controlMonochromatic light (190 nm- 800nm) is passed through cellIntensity of light transmitted is detectedWavelength varied to test absorption at different energies
6 Ultraviolet-Visible Spectroscopy Light transmitted (T) through the sample:T = (I/I0)I=Light intensityI0=Initial light intensityBeer-Lambert Law of Absorbance (A):A = -log(I / I0) = εbcε= molar absorptivity (L/mol*cm)b=pathlength of sample cell (cm)c=concentration of compound (mol/L)
7 Example Absorption spectrum NO3Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies
8 Gas Chromatography-UV-Vis Sample evaporated into gas phaseSample injected into columnAnalytes interact with stationary phase in column to different extentsAllows separation of different analytesDetection by UV-Vis
9 Advantages/Disadvantages UV-Vis detection for GC General indicator of functional groupsMinimal damage to sampleGood quantitationUsing GC eliminates solvent effectsDisadvantages:Lack of sensitivity & selectivityLimited to UV-Vis absorbing compounds
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