Environmental Chemistry

Robert N Slinn

South Cheshire College and

Staffordshire University

THERMAL INVERSION

Types of Thermal Inversions

• Radiative: Earth cools during night by

radiating thermal energy into space. In

morning, air near surface will be cooler

than air above creating thermal

inversion. More frequent, but less

problematic and persistent than -

• High pressure subsidence: high pressure

mass of air moves towards earth. Is

compressed and heated, causing thermal

inversion some distance above ground.

Air Pollution System

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

AIR POLLUTANTS

• Sulfur containing compounds

• Nitrogen containing compounds

• Carbon containing compounds

• Halogen containing compounds

• Toxic substances

• Radioactive compounds

AVERAGE COMPOSITION OF THE

ATMOSPHERE

Element Parts per 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

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 atmospheric

constituents. (Ozone, photochemical

oxidants)

Atmospheric Concentration

Units

Two concentrations commonly used:

1. concentration (micrograms/cubic meter)

2. parts-per-million volume (ppm)

Criteria Pollutants

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 produce

sulfuric acid - major component of acid

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

H2SO4

Nitrogen-Containing Compounds• Nitrous oxide (N2O): colorless, odorless,

“laughing gas”, emitted by natural sources,

chemically inert, not considered an air

pollutant.

• Nitric oxide (NO) + nitrogen dioxide (NO2) =

NOx: emitted by combustion at high

temperatures. Together with hydrocarbons

are important in formation of ozone. Lifetime

about 1 day. Combines with water to form

nitric acid, component of acid rain.

• Released by stationary and mobile sources.

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

Carbon Monoxide

• Carbon monoxide is a colorless, odorless,

poisonous gas formed when carbon in fuels is

not burned completely.

• It is a byproduct of highway vehicle exhaust,

which contributes about 60 percent of all CO

emissions nationwide. In cities, automobile

exhaust can cause as much as 95 percent of all

CO emissions. These emissions can result in

high concentrations of CO, particularly in local

areas with heavy traffic congestion.

• Other sources of CO emissions include industrial

processes and fuel combustion in sources such

as boilers and incinerators.

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

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

OZONE

• Secondary pollutant: O3

• Formed in atmosphere by reaction of oxides

of nitrogen, VOC and sunlight.

• Classified as a criteria pollutant

• Major component of photochemical smog