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Air Quality Monitoring

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  1. Reading: Chap 7.1 & 7.2 Air Quality Monitoring ENV 4101/5105 Elements of Air Pollution Aerosol & Particulate Research Lab

  2. Monitoring Considerations • Manual vs. automated (real-time, continuous) monitoring • Sampling time • Federal reference method (FRM) vs. equivalent method (EM) • Monitoring of Ambient Air Pollutants • SO2, NOx, CO, O3 • Hydrocarbons • PM10, PM2.5 • Source Sampling and Monitoring • Sampling train • Isokinetic sampling • Quality Assurance Programs • Quality Assurance • Quality Control • Air Quality Monitoring Network Air Quality Monitoring What’s the use of ambient air quality monitoring data? Aerosol & Particulate Research Lab

  3. Monitoring Considerations What are the objectives? Examples of criteria for selecting ambient sampling locations? • Sampling location: limited number of fixed site monitors whose locations reflect objectives of air quality monitoring program • Lower limit of detection (LOD): a sufficient amount of pollutant must be collected, f(sampling rate, duration) • Integrated sampling vs. real-time sampling • Area sampling vs. personal sampling • Collection efficiency of the instrument: • Low flow rate for gas-phase contaminants (< 1 L/min) Aerosol & Particulate Research Lab

  4. Differences in averaging times associated with real-time data Which duration should you use? Aerosol & Particulate Research Lab

  5. National Ambient Air Quality Standards Why different durations? Aerosol & Particulate Research Lab

  6. Federal Reference Methods for Criteria Pollutants Aerosol & Particulate Research Lab

  7. FRM - Spectrophotometry (pararosanilne method) Air sample  potassium tetrachloromercurate solution  HgCl2SO3-2  react with HCHO and colorless pararosaniline hydrochloride  red-violet product  measured spectrophotometrically  SO2 concentration EM – FT- IR Spectrometry (Absorption of IR by SO2 in the air  SO2 concentration) SO2 Aerosol & Particulate Research Lab

  8. SO2 EM – UV Fluorescence 1) UV light excites SO2 to a higher energy state SO2 + hv1  SO2* 2) Decay of the excited SO2*, emitting a characteristic radiation SO2*  SO2 + hv2 Aerosol & Particulate Research Lab

  9. FRM – Gas-Phase Chemiluminescence Chemiluminescence: emission of light from electronically excited chemical species formed in chemical reactions. NO + O3 NO2* + O2 NO2*  NO2 + hv Measurement of NO2: conversion of NO2 to NO, and subsequent measurement by chemiluminescence. 2NO2 + Mo  3 NO + MoO3 Possible interference: N-containing compounds  higher measured NO2 NO – NO2 – NOx EM – FT- IR Spectrometry Can you design an instrument that can measure the concentration of both NO and NO2 in the air? Aerosol & Particulate Research Lab

  10. FRM – Nondispersive Infrared (NDIR) spectrometry CO strongly absorbs infrared energy at certain wavelengths. Detection device: two cylindrical cells, a sample and a reference cell. Difference in infrared energy in the two cells  concentration of CO CO CO Reference Cell Sample Cell ~ IR ~ Detection Aerosol & Particulate Research Lab

  11. O3 UV light (254 nm) Detector O3 FRM – Chemiluminescence Light emissions produced on reaction of O3 with ethylene (C2H4). C2H4 flammable – replaced by Rhodamine B dye embedded in a disk Rhodamine B does not attain a stable baseline rapidly after exposure to O3 EM – UV Photometry Absorption of UV light (254 nm) by O3 and subsequent use of photometry to measure the reduction of UV energy O3 What would cause an interference on a UV photometry O3 monitor? Aerosol & Particulate Research Lab

  12. FRM – Gas Chromatography - FID Intensity Time NMHCs Stationary and mobile phases GC-Detector: Generate an electronic signal when a gas other than the carrier gas elutes from the column. Aerosol & Particulate Research Lab

  13. NMHC • Mass sensitive rather than concentration sensitive • FID – Flame Ionization Detection: • Combustion of organic substances • Positive ions (+) and electrons (-) are formed when burned – change in current Aerosol & Particulate Research Lab

  14. Impaction and filtration are the primary PM collection principles • Measure the weight of exposed and clean filters • High-volume sampler (Hi-Vol) • Typical sampling duration – 24 h Animation – PM10 Impactor • PM10 Sampler • Remove particles > 10 µm by impaction on a greased surface • Particles < 10 µm collected on a quartz glass fiber filter Particulate Pollutants What does the PM10 sampler measure? Number or mass concentration of particles? PM10 sampler with size-selective inlet Aerosol & Particulate Research Lab

  15. Animation – Virtual Impactor TEOM Series 1400abAmbient Particulate Monitor Thermo Electron Co. Dichotomous Sampler • Equivalent method: TEOM • Measure PM10, PM2.5, TSP • Tapered element oscillating microbalance • Real-time measurement of particle mass collected on a filter How can a Dichotomous sampler measure coarse (PM2.5-10)and fine (PM2.5) particles? Aerosol & Particulate Research Lab

  16. Aerosol flow In Clean air out Animation – Cascade Impactor Cascade Impactor How can we collect different sizes of particles using cascade impactor? Aerosol & Particulate Research Lab

  17. Source Sampling and Monitoring • Stack Sampling of PM • Probe inserted into the stack • Temperature sensor • Pitot tube – gas velocity and flow rate • Two-module sampling unit • Isokinetic Sampling • Particles – inertial forces • Samples must be collected at the same rate of low as the stack gas What’s the use of source emission data? Aerosol & Particulate Research Lab

  18. Isokinetic Sampling Fig 8 -2, Aerosol Measurement, 2nd Edition, 2001 Aerosol & Particulate Research Lab

  19. Continuous Emission Monitoring (CEM) Opacity • Compare plume darkness to Ringlemann chart by trained smoke readers • Averages of measurements of ¼ or ½ minute over an hour • Simple, low cost, legal acceptance Ringlemann chart Certain utilities and industrial sources are required to measure stack emission continuously SO2, NO2, opacity, CO2, TRS, H2S, Hg Aerosol & Particulate Research Lab

  20.  Bias  Precision Relative Error: Coefficient of variation: Accuracy, Precision and Bias Accuracy is a combination of random (precision) & systematic (bias) errors. Which of the 3 cases has the highest accuracy? Why? Aerosol & Particulate Research Lab

  21. Calibration • Often used for adjusting bias-type errors • Measured values are compared to standard reference values (for pollutant concentration) or standard airflow measuring techniques/devices (for volume air flow) • Primary vs. secondary standard for flow: traceable to the National Institute of Standards and Technology (NIST) • Primary: bubble meter • Secondary: wet or dry test meters calibrated by bubble meter • Gas standards: traceable to a NIST reference material • CO, SO2, NO2, NO: available in cylinder gas or permeation tubes • O3: NIST certified O3 generator Aerosol & Particulate Research Lab

  22. Goal: Valid and reliable air quality monitoring data • Quality Assurance (QA) • Setting policy and overseeing management controls • Planning, review of data collection activities and data use • Setting data quality objectives, assigning responsibilities, conducting reviews, and implementing corrective actions • Quality Control (QC) • Technical aspects of data quality programs • Implementation of specific QC procedures: calibrations, checks, replicate samples, routine self-assessment, and audits Quality Assurance Programs It is federal rule to document QA/QC efforts ! Aerosol & Particulate Research Lab

  23. State and Local Air Monitoring Stations (SLAMS) • Highest pollutant concentrations • Representative concentrations in areas of high population density • Impact of major emission sources • Regional background concentrations • Extent of pollutant transport among populated areas • Welfare-related impacts in more rural and remote areas • National Air Monitoring Stations (NAMS) • Urban area, long-term air quality monitoring network • Air quality comparisons and trends analysis Air Quality Monitoring Network • Photochemical Assessment Monitoring Stations (PAMS) • Monitor O3 and photochemical air pollutants • Clean Air Status and Trends Network (CASTNet) • Primary source for rural O3 level and dry atmospheric deposition • National Atmospheric Deposition Program (NADP) • Assess the problem of atmospheric deposition and its effects on aquatic and terrestrial ecosystems (H+, NH4+, SO42-, NO3-, Cl-, Ca2+, Mg2+, K+, Hg) Aerosol & Particulate Research Lab

  24. Monitoring Considerations • Manual vs. automated (real-time, continuous) monitoring • Sampling time • Federal reference method (FRM) vs. equivalent method (EM) • Monitoring of Air Pollutants • SO2, NOx, CO, O3 • Hydrocarbons • PM10, PM2.5 • Source Sampling and Monitoring • Sampling train • Isokinetic sampling • Quality Assurance Programs • Quality Assurance • Quality Control • Air Quality Monitoring Network Quick Reflections Aerosol & Particulate Research Lab