lecture 4 air pollution measurements.ppt

Dichotomous Sampler http://crac.ucc.ie/images/sampler1.jpg How can a Dichotomous sampler measure coarse (PM2.5-10) and fine (PM2.5) particles? Animation – Virtual Impactor TEOM Series 1400abAmbient Particulate Monitor Thermo Electron Co. Equivalent method: TEOM Measure PM10, PM2.5, TSP Tapered element oscillating microbalance Real-time measurement of particle mass collected on a filter * * Cascade Impactor Animation – Cascade Impactor How can we collect different sizes of particles using cascade impactor? Aerosol flow In Clean air out * * 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? Isokinetic Sampling * * Fig 8 -2, Aerosol Measurement, 2nd Edition, 2001 Continuous Emission Monitoring (CEM) Certain utilities and industrial sources are required to measure stack emission continuously SO2, NO2, opacity, CO2, TRS, H2S, Hg * * Opacity Ringlemann chart Compare plume darkness to Ringlemann chart by trained smoke readers Averages of measurements of ? or ? minute over an hour Simple, low cost, legal acceptance Accuracy, Precision and Bias Accuracy is a combination of random (precision) systematic (bias) errors. Which of the 3 cases has the highest accuracy? Why? * * Relative Error: Coefficient of variation: ? Bias ? Precision 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: