Typical mixing ratios for some compounds of environmental importance

Carbon dioxide 355 ppm Carbon monoxide 100 ppb to 20 ppm Ozone 1 to 100 ppb Methane 1.72 ppm Nonmethane hydrocarbon 1 ppt to < 1 ppb Nitric oxide (NO) 5 ppt to 1 ppb Nitrogen dioxide (NO2) 1 to 150 ppb Nitrous oxide (N2O) 310 ppb Sulfur dioxide 1 to 100 ppb CFCl3 (Freon 11) 200 ppt CF2Cl2 (Freon 12) 350 ppt

Atmospheric structure

atmospheric pressure

The atmospheric pressure is the weight exerted by the overhead atmosphere on a unit area of surface

A Bh

vacuum

Mercury barometer

ghP HgA

Units for pressure

• International System of Units: Pascal (N/m2)• Hectopascal (hPa)• mm Hg or Torr• Millibar (mbar)• psi (lb/in2)

1 atm = 1.01325 x 105 Pascal (Pa) = 1.01325 x 103hPa

1 atm = 760 mmHg = 760 Torr1 atm = 1013.25 mbar

1 atm = 14. 7 psi

The ozone layer

Ultraviolet protection by ozone

Ozone absorbs UV light in the solar irradiation that is harmful to life

Amount of UV Radiation That Reaches Earth’s Surface

Ozone formation and destruction in the stratosphere

• The major natural carrier of chlorine to the stratosphere is CH3Cl

CF2Cl2 2 Cl. + other products

CFCl3 3 Cl. + other products

The Montreal Protocol

Stratospheric Ozone DepletionMeasurement Techniques

TOMS-Total Ozone Mapping Spectrometer

Polar vortex

ONE-BOX MODEL

CO formation from methane oxidation

CH4 + OH CH3 + H2O

+O2

C O

H

H

H

CH3OO

NONO2

+O2

CH H

O

+ HO2

hv

H

O+ HO2

O2

HO2

CO

Sulfur gases

-2 +4 +6H2SHydrogen sulfide(CH3)2SDimethylsulfide (DMS)CS2Carbon disulfideCOSCarbonyl sulfide

SO2Sulfur dioxide

H2SO4Sulfuric acidSO4

2-

Sulfate

Decreasing oxidation number (reduction reactions)

Increasing oxidation number (atmospheric oxidation)

The sulfur cycle

Sources of SO2: Natural ~42 Tg(S) Anthropogenic ~78 Tg (S)

Necessary ingredients for ozone formation

CH4 + .OH + O2 CH3OO. + H2O

CH3OO. + NO CH3O. + NO2

CH3O. + O2 HCHO + HO2.

HO2. + NO .OH + NO2

NO2 + h NO + O (2x)

O + O2 + M O3 + M (2x)

Net: CH4 + 4 O2 HCHO + H2O + 2 O3

VOC

Sunlight

Photochemical air pollution

1

Greenhouse

Glass, the material that greenhouse is made of, 1) transmit short-wavelength visible light, 2) absorbs and redirects the longer wavelengths of energy. These two aspects make the greenhouse warmer than outside air temperature.

Natural Greenhouse effect

The natural greenhouse effect causes the mean temperature of the Earth's surface to be about 33oC warmer than it would be if natural greenhouse gases were not present.

Enhanced greenhouse effect

When concentrations of greenhouse gases increase, more infrared radiation is returned toward the earth and the surface temperature rises.