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Primary pollutant are those pollutants that are directly emitted from for their sources. Like CO2, CO as these gaseous are directly emitted form burning of fossil fuel.
Secondary pollutants are those which are formed from the combination of primary pollutants with some other compound. Like smog which is formed by combination of smog and fog. And pesticides, insecticide
Primary pollutants enter the atmosphere directly from a process like combustion of fuel in an engine releasing carbon monoxide and carbon dioxide out of the exhaust. Another example is sulfur dioxide released in a power plant or factory from combustion of fossil fuel. A volcanic eruption releases smoke and ash which are considered primary pollutants. Nitrogen oxides are produced by combustion of fossil fuels at high temperature or by thunderstorms. These are but a few examples. Secondary pollutants form when primary pollutants interact with something else in the air and it forms something else entirely. For example, when nitrogen oxides react under conditions of high temperatures, with volatile organic compounds, ground level ozone is created. This is a secondary pollutant that can lead to the production of smog and poor air quality. Smog, a combination of smoke and fog can be the result of burning coal which releases smoke and sulfur dioxide. Or, it can be the result of cars and factories releasing emissions that interact with UV light from the sun to form secondary pollutants.
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