Air Stack sampling Most pollutants in air come from industrial plants fuelled by coal or other fossil fuels. Such plants include pulp and paper mills, metal smelters, and oil and gas processors. They regularly pump gases into the air via smokestacks. These gases contain chemicals like sulphur, mercury, and carbon. Gaseous chemicals that are released into the air are called emissions (see Figure 1.25).
Figure 1.25 Techniques for monitoring emissions have changed over the years. In 1925, P.D. Buckley worked as a smoke observer. He watched the colour of the smoke coming out of the New York Edison Company’s smokestacks. Buckley’s “tests” were supposed to help the company burn less coal.
The government of Canada has standards about the levels of emissions that industries are allowed to pump into the air. These standards require industries to have emissions with lower levels of sulphur and carbon. Companies must regularly sample and monitor the gases that come out of smokestacks to make sure they are up to standards. They use a method called stack sampling. A stack test uses equipment that samples the stream of gas coming out of a smokestack when it is working. One or more probes are inserted into the ports on the stack. These probes are attached to tubes called sample lines (see Figure 1.26). The probes remove some of the gas coming out of the stack. Then, the sample lines carry the sample to a detection and analysis station. Here, a computer measures the pollutants in the gas.
Monitoring the quality of air over time Earlier you learned that the main component of smog is ground-level ozone (O3). The other main ingredient of smog is fine particulate matter. Fine particulate matter is a mix of solid particles and liquid droplets in the air. It includes things like aerosols, smoke, and dust. It is formed from chemical reactions in the atmosphere and through burning fuel (e.g., motor vehicles, wood stoves). Fine particulate matter is also known as PM2.5 because its particles measure 2.5 µm or less in diameter. (µm is the symbol for a micrometre, which equals one millionth of a metre. A strand of human hair is about 100 µm wide.) Because it is so small, people can inhale PM2.5 into their lungs. This can cause serious health problems. © Edvantage Interactive, 2010
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Chapter 1
Figure 1.26 Stack sample lines run up the side of a smokestack to the sample ports, where they can take samples of air from inside the stack.
We are the Guardians of Earth’s Spheres
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