POLLUTANTS
The Global Atmosphere Watch was established in 1989 by the World Meteorological Organization to coordinate atmospheric pollution measurement. The primary measurements are determined for:•
greenhouse gasses (carbon dioxide, chlorofluorocarbons, methane, nitrous oxide)•
ozone and precursor gases (total column, vertical profile, and near the surface)•
the turbidity of atmosphere, UV intensity, aerosol particles, and water vapor•
particle concentration and composition of rain•
reactive gas concentrations (sulfur dioxide, nitrogen oxides, reduced nitrogen species, carbon monoxide)•
heavy metal concentrations•
presence of radionuclides (krypton-85, radon-222, beryllium-7, and lead-210) and concentrations.
The WMO is developing methods of testing and calibration to achieve worldwide comparability of results. 22 global stations and many regional stations are included in the program.
The Environmental Protection Agency publishes procedures for testing pollutants. Test methods can also be found in a specialized monograph.15 Test methods are briefly reviewed below. EPA methods can be found on their website (www.epa.gov).
4.6.1 CARBON DIOXIDE
EPA Methods 3A and 3B can be used to determine carbon dioxide by gas analysis using either an Orsat or a Fyrite analyzer. The sensitivity of the method is 2000 ppmv. Orsat apparatus, given in Figure 4.25, is designed for Method 3 to determine CO2, CO and O2 concentrations in the effluent gas stream.
4.6.2 PARTICULATE MATTER
EPA Method 5 can be used to determine particulate matter emitted from stationary sources. Particulate matter is collected on a glass fiber filter and determined gravimetrically after removal of water (excluding combined water). Modern methods of particle matter analysis include Scanning Mobility Particle Sizer Spectrometer (Figure 4.26) and Fast Mobility Particle Sizer Spectrometer (Figure 4.27).15 Scanning Mobility Particle Sizer Spectrometer 3938 measures particles from 1 to 10,000 nm and displays data using up to 167 actual size channels. The Fast Mobility Particle Sizer 3091 spectrometer measures particles in the range from 5.6 to 560 nm, offering a total of 32 channels of resolution (16 channels per decade). It uses an electrical mobility measurement technique similar to that used in Scanning Mobility Particle Sizer Spectrometer. However, the Fast Mobility Particle Sizer Spectrometer uses multiple, low-noise electrometers for particle detection. This produces particle-size-distribution measurements with one-second resolution, providing the ability to visualize particle events and changes in particle size distribution in real time.
4.6.3 SULFUR DIOXIDE
Three EPA methods (6A, 6B, and 6C) are used to measure sulfur dioxide concentration. In Methods 6A and 6B, a sample of the absorbed gas is measured by the barium-thorin titration (sensitivity 3.4 mg SO2/m3). EPA Method 8 also uses the barium-thorin titration to determine sulfuric acid mist. Methods 6C offer a choice of methods using one of UV spectrophotometry, nondispersive infrared spectrophotometry, or fluorescence analyses. Continuous monitoring can be performed either by UV fluorescence or spectrophotometric analysis after forming a stable sulfitomercurate complex.16 Brewer spectrophotometer (Figure 4.11) measures SO2 concentration in addition to total ozone column and UV spectrum measurements.
4.6.4 NITROGEN OXIDES
Several methods approved by EPA can be used to determine nitrogen oxides (NOx). EPA Method 7 describes the colorimetric determination of nitrogen oxides using a phenoldisulfonic acid procedure. Method 7A defines the ion chromatographic measurement of nitrogen oxides (excluding nitrous oxide) with a sensitivity of 65-655 ppmv. Ultraviolet spectrophotometry is used in Method 7B which determines nitrogen oxides (excluding nitrous oxide) with sensitivity of 30-786 ppmv. Method 7C uses oxidation by potassium permanganate solution followed by the colorimetric determination of all nitrogen oxides.
It provides a sensitivity of 7 ppmv. An oxidation is used in Method 7D but the determination is done by the ion chromatographic method (sensitivity is the same – 7 ppmv). Finally, there is the EMTIC TM-007E method which uses chemiluminescence and which determines the NO present originally and that converted from NO2. Serinus 40 (Figure 4.28) is EPA approved analyzer for ambient NO/NO2/NOx monitoring. It uses chemiluminescence technology to measure NOx in the ambient air.
4.6.5 CARBON MONOXIDE
EPA Method 10B describes a method to separate CO by gas chromatography followed by a reduction to methane for a final determination by a flame ionization detector. Orsat analyzer (Figure 4.25) measures CO concentration in stream of gas.
4.6.6 OZONE
Ozone is absorbed into a potassium iodide solution where the iodide quantitatively converts to iodine. The liberated iodine is determined by spectroscopic method against a master curve. Ozone can be determined by ultraviolet analysis.17
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