Environmental Chemistry

1. Environmental Chemistry
Robert N Slinn
South Cheshire College and
Staffordshire University

2. THERMAL INVERSION

3. 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.

4. Air Pollution System

5. 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

6. AIR POLLUTANTS
• Sulfur containing compounds
• Nitrogen containing compounds
• Carbon containing compounds
• Halogen containing compounds
• Toxic substances
• Radioactive compounds

7. 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

8. 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)

9. Atmospheric Concentration
Units
Two concentrations commonly used:
1. concentration (micrograms/cubic meter)
2. parts-per-million volume (ppm)

10. Criteria Pollutants

11. 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

14. 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.

15. 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

16. 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.

17. 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

18. 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

19. 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