Environmental Environmental Engineering and Engineering and

SafetySafetyLecture #3Lecture #3

Primary Air Pollutants Primary Air Pollutants - A primary pollutant is one that is emitted into the atmosphere directly from the source of the pollutant and retains the same chemical form.

Secondary Air Pollutants Secondary Air Pollutants - Primary pollutants interact with one another, sunlight, or natural gases to produce new and harmful compounds.

Primary PollutantsPrimary Pollutants

►Carbon monoxide Carbon monoxide ►Sulfur dioxideSulfur dioxide►Nitrogen oxidesNitrogen oxides►Particulate matterParticulate matter►Volatile Organic Compounds (VOCs)Volatile Organic Compounds (VOCs)

► Incomplete oxidation of carbon.Incomplete oxidation of carbon.► The natural anaerobic decompositionThe natural anaerobic decomposition of carbonaceous materials by soil of carbonaceous materials by soil microorganisms also release CO.microorganisms also release CO.► Also results by the oxidation of CH4.Also results by the oxidation of CH4.

► Anthropogenic sources Anthropogenic sources ► include motor vehicles, fossil fuel burning for include motor vehicles, fossil fuel burning for

electricity, industrial processes etc. motor electricity, industrial processes etc. motor vehicles account for 60-80% of the emissionvehicles account for 60-80% of the emission

Carbon monoxideCarbon monoxide

Carbon monoxideCarbon monoxide

►Since no significant change in global co Since no significant change in global co has been observed over past 20 years, has been observed over past 20 years, yet the worldwide contribution of yet the worldwide contribution of anthropogenic source has been anthropogenic source has been doubled over the same time period. doubled over the same time period. Two reasons areTwo reasons are

►Reaction with hydroxyl radicals to form Reaction with hydroxyl radicals to form carbon dioxidecarbon dioxide

►Removal by soil microorganisms.Removal by soil microorganisms.

HydrocarbonsHydrocarbons

►Methane and terpenes are the major Methane and terpenes are the major hydrocarbons that are emitted.hydrocarbons that are emitted.►The major anthropogenic source is partially The major anthropogenic source is partially burned gasoline which account for 38 % of burned gasoline which account for 38 % of global emission. Refinery losses and solvent global emission. Refinery losses and solvent evaporation account for another 27 %evaporation account for another 27 %►Many of the hydrocarbons are oxidized. Many of the hydrocarbons are oxidized. Several are converted to other organic Several are converted to other organic compounds in the presence of nitrogen oxides compounds in the presence of nitrogen oxides . .

LeadLead

► Volcanic activity are the primary natural Volcanic activity are the primary natural sources of atmospheric lead. smelting and sources of atmospheric lead. smelting and refining as well as incineration lead refining as well as incineration lead containing wastes are major sources of lead.containing wastes are major sources of lead.

► Smaller particles attach to larger particles, Smaller particles attach to larger particles, once they have attained the size of several once they have attained the size of several microns, they either settle out or are microns, they either settle out or are washed out by rain.washed out by rain.

Nitrogen oxide:Nitrogen oxide:

►Bacterial action in soil releases nitrous Bacterial action in soil releases nitrous oxides ( N2O)oxides ( N2O)

► In the stratosphere nitrous oxide reacts In the stratosphere nitrous oxide reacts with atomic oxygen and form nitric oxide with atomic oxygen and form nitric oxide (NO)(NO)

►Nitric oxide further reacts with ozone to Nitric oxide further reacts with ozone to form nitrogen dioxide. About 96 % NOform nitrogen dioxide. About 96 % NO22 comes from anthropogenic sourcescomes from anthropogenic sources

►Nitrogen oxides are removed by acid rain.Nitrogen oxides are removed by acid rain.

Sulfur OxidesSulfur Oxides

►They may be both primaryThey may be both primary

as well as secondary pollutants. as well as secondary pollutants.

►Sox are primary pollutantsSox are primary pollutants

While H2S is secondary While H2S is secondary

►The combustion of fossil fuels containing S The combustion of fossil fuels containing S yields SO2.yields SO2.►Because combustion is not 100 % efficient, we Because combustion is not 100 % efficient, we generally assume 5% of sulfur end up with ash.generally assume 5% of sulfur end up with ash.

Particulate MatterParticulate Matter

► Particulates - small pieces of solid materials Particulates - small pieces of solid materials and liquid droplets and liquid droplets

► Examples: ash from fires, dust storms, sea Examples: ash from fires, dust storms, sea salts volcanic particles etcsalts volcanic particles etc

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Photochemical oxidantsPhotochemical oxidants

►Unlike other pollutants photochemical Unlike other pollutants photochemical oxidants are released entirely by the oxidants are released entirely by the atmospheric reactions ,thus they are called atmospheric reactions ,thus they are called secondary pollutantssecondary pollutants..►They start by absorption of photon by an They start by absorption of photon by an atom, molecule, free radical, or ion. atom, molecule, free radical, or ion. ►Ozone is principal photochemical oxidant.Ozone is principal photochemical oxidant.►Photochemical smogPhotochemical smog