Enviro Chemistry 1250692300 Phpapp01

8/3/2019 Enviro Chemistry 1250692300 Phpapp01

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Environmental Chemistry

Robert N Slinn

South Cheshire College andStaffordshire University


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THERMAL INVERSION


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Types of Thermal Inversions

Radiative: Earth cools during night byradiating thermal energy into space. In

morning, air near surface will be cooler

than air above creating thermalinversion. More frequent, but less

problematic and persistent than -

High pressure subsidence: high pressuremass of air moves towards earth. Is

compressed and heated, causing thermal

inversion some distance above ground.


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Air Pollution System


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TYPES OF EMISSIONS

Stationary Sources power plants, factories, industrial sites

Mobile Sources

cars, trucks, buses, trains, planes,aircraft, off-road vehicles

Area Wide Sources

agriculture, paved and unpaved roads,construction

Natural Sources

biogenic, wildfires, windblown dust


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AIR POLLUTANTS

Sulfur containing compounds

Nitrogen containing compounds

Carbon containing compounds

Halogen containing compounds

Toxic substances Radioactive compounds


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AVERAGE COMPOSITION OF THE

ATMOSPHERE

Element Parts er Million Nitrogen 780,800

Oxygen 209,500

Argon 9,300

Carbon Dioxide 300

Neon 18.2

Helium 5.2

Krypton 1.1

Hydrogen 0.5

Nitrous Oxide 0.5


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Primary and Secondary

Pollutants Primary Pollutants: Those emitted directly

from sources (CO, SO2, VOC, CO, lead,

PM)

Secondary Pollutants: Those formed in the

atmosphere by chemical interactions among

primary pollutants and normal atmosphericconstituents. (Ozone, photochemical

oxidants)


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Atmospheric Concentration

UnitsTwo concentrations commonly used:

1.concentration (micrograms/cubic meter)

2.parts-per-million volume (ppm)


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Criteria Pollutants


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Sulfur Containing Compounds

Carbonyl sulfide (COS), carbon disulfide(CS2), dimethl sulfide ((CH3)2)S), hydrogen

sulfide (H2S), sulfur dioxide (SO2) Sources are: biological decay, combustion

of fossil fuels and organic matter.

SO2 combines with water to producesulfuric acid - major component of acid

rain: 2SO2 + O2 = 2SO3: SO3 + H2O =

H2SO4


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Nitrogen-Containing Compounds

Nitrous oxide (N2O): colorless, odorless,laughing gas, emitted by natural sources,

chemically inert, not considered an airpollutant.

Nitric oxide (NO) + nitrogen dioxide (NO2) =NOx: emitted by combustion at hightemperatures. Together with hydrocarbonsare important in formation of ozone. Lifetimeabout 1 day. Combines with water to formnitric acid, component of acid rain.

Released by stationary and mobile sources.


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Carbon Compounds

CO - carbon monoxide: criteria pollutant,

colorless, odorless gas. Toxic - binds to

hemoglobin preventing uptake of oxygen.Formed by incomplete combustion mainly

in cars and trucks. Lifetime in atmosphere

about one month


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Carbon Monoxide

Carbon monoxide is a colorless, odorless,

poisonous gas formed when carbon in fuels isnot burned completely.

It is a byproduct of highway vehicle exhaust,which contributes about 60 percent of all CO

emissions nationwide. In cities, automobileexhaust can cause as much as 95 percent of allCO emissions. These emissions can result inhigh concentrations of CO, particularly in localareas with heavy traffic congestion.

Other sources of CO emissions include industrialprocesses and fuel combustion in sources suchas boilers and incinerators.


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Particulates

Particles of average diameter 10 microns or

less (PM10). Tend to be easily inhaled and

lodge in lungs. Larger particles not readily

inhaled.

Sources are combustion process (particular

diesel combustion), unpaved roads, fires.

PM2.5 particles with average diameter less

than 2.5 microns. Considered even more

problematic than PM10

New EPA regs. For PM2.5 now under

consideration


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Reactive Organic Compounds

(ROG) and Ozone Sometimes called VOC (volatile organic

compounds or hydrocarbons)

Gasoline contains almost 100 hydrocarbons,such as octane, heptane, ethane.

Evaporation of gasoline one source of HC

into atmosphere Natural sources account for 85% of HC in

air, but more reactive ones are

anthropogenic


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OZONE

Secondary pollutant: O3

Formed in atmosphere by reaction of oxides

of nitrogen, VOC and sunlight.

Classified as a criteria pollutant

Major component ofphotochemical smog


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Enviro Chemistry 1250692300 Phpapp01