Air Pollution

“Air” is the earth’s atmosphere• Air is tasteless, odorless,

invisible• We can feel its presence:

wind, heat, cold• We depend on it for our

existence• If we can see or smell air,

that’s pollution

Our atmosphere is a mixture of gases

Gases exert pressure in their environment

• molecules in constant motion

• colliding with each other, walls of container

• collisions create pressure

• pressure is force per unit area

• “atmospheric pressure” or “barometric pressure”

• “1 atmosphere” or 1 atm is equal to:– 14.7 pounds per square inch– 760 torr– 760 millimeters of Hg

• scientific use: 1 bar or 1 atm

Gases occupy a large volume

• Application: air bags• Impact trips a sensor that activates the reaction:

• The gaseous product of the reaction occupies 450 times more space than does the solid reactant.

The atmosphere is a layered structure

• Ionosphere

– aurora borealis

• Mesosphere

– small meteors

• Stratosphere

– ozone layer

• Troposphere

– life, weather, pollutants

lowest pressure

highest pressure

Pressure decreases with increasing altitude

http://www.atmo.arizona.edu/students/courselinks/fall14/atmo336/lectures/sec1/structure.html

Temperature also changes with altitude

http://www.atmo.arizona.edu/students/courselinks/fall14/atmo336/lectures/sec1/structure.html

Ozone absorbs UV radiation in the stratosphere• Two types of UV light : UV-A and UV-B• UV-B is shorter in wavelength and higher in energy.

• Excessive exposure to UV-B increases risks of skin cancer, cataracts, and a weakened immune system.

• Chemical reactions produce and use ozone• Ozone absorbs UV-B

O3 + UV light O2 + O

O2 + O O3 + heat

Air pressure can affect the human body

• Pressure is proportional to the number of gas molecules

• Tympanic cavity in ears

• Air flight: “popping” ears

Gas laws explain the behavior of gases

• Fundamental properties of gases:– Pressure (represented by P)– Amount (measured in moles, represented by n)– Volume (usually expressed in liters and represented by V)– Temperature (expressed in Kelvin (K) and represented by T)

• If one changes, the others will also change.

• Gas laws explain the behavior of gases

• Gas laws allow behavior to be predicted.

Boyle�s Law• In 1662, Robert Boyle confirmed that if the pressure

increases at constant temperature, volume will decrease.

• So, pressure and volume are inversely related:

P1V1 = P2V2

• Molecules in a smaller space collide more frequently • More collisions gives higher pressure

Example

• A weather balloon is inflated to a volume of 55.0 L at sea level where the atmospheric pressure is 755 mm Hg. Find the volume of the balloon as it rises to an altitude where the atmospheric pressure reduces to 135 mm Hg. (Assume constant temperature.)

http://www.noaa.gov/news/fifty-years-ago-historic-balloon-launch-changed-way-we-see-ozone-layer

• V1 = 55.0 L P1 = 755 mm Hg constant T• P2 = 135 mm Hg V2 = ?

• Boyles Law: P1V1 = P2V21 1

22

2

=

755 mm Hg =

PVVP

V´ 55.0 L

135 mm Hg = 308 L

Charles’ Law

• In the 1780’s, Jacque Charles found that if the temperature (in degrees Kelvin) of a gas is increased at constant pressure, its volume will increase.

• So, temperature (in K) and volume are directly related:

• As molecules absorb heat energy, they gain energy

• Energetic molecules need more – volume increases

=1 2

1 2

V VT T

Example• A balloon was filled at an initial temperature of 25ºC

and an initial volume of 3.0 L. What would be its volume at −15ºC? (Assume constant pressure.)

• V1 = 3.0 L T1 = 25ºC constant P• V2 = ? T2 = −15ºC

• Use Charles Law: T must be in Kelvins

• Temperature conversion to K:

• Solving for V2: = 2 12

1

258 K = T VVT

´ 3.0 L298 K

= 2.6 L

o o1 2 = 25 C +273 = 298 K = -15 C +273 = 258 KT T

Combined Gas Law

• Sometimes more than one property of a gas changes at one time.

• The Combined Gas Law combines Boyle�s Law and Charles� Law.

=1 1 2 2

1 2

PV PVT T

Example

• P1 = 1.00 atm V1 = 53 L T1 = 25ºC• P2 = 0.40 atm V2 = ? T2 = −20.º C

• Combined Gas Law: T must be in Kelvin

• Temperature conversion to K:

• Solving for V2:

=1 1 2 2

1 2

PV PVT T

= 1 2 12

2 1

1.00 atm = PTVVPT

´ 253 K ´ 53 L0.40 atm ´ 298 K

´ 2 = 1.1 10 L

o o1 2 = 25 C + 273 = 298 K = -20 C + 273 = 253 KT T

• A weather balloon is initially inflated to a volume of 53.0 L at a pressure of 1.00 atm and a temperature of 25ºC. The balloon then levels off at an altitude where the atmospheric pressure drops to 0.40 atm and the temperature drops to −20.ºC. What will be the volume of the balloon at the final altitude?

Ideal Gases

What is an ideal gas?• a hypothetical, model substance• gas atoms/molecules/ions take up no space• there are no forces present

All gases behave ideally at • sufficiiently low pressure• sufficiently high temperature• +/- 1% at 1 atm, 273 K

Gas laws explain behavior of gases

• Ideal Gas Law includes the amount of gas as n

• Equation needs an extra number R to make left = right

• R is called the gas constant

• PV=nRT

• applies to “ideal” gases, not real ones, but still useful

– no intermolecular forces

– atoms/molecules take up no volume

From Definition to Measurement

Units of Pressure

Gas Constant

A Study of How Three Gases Behave

PV=RT• PV is constant at constant temperature• Obtain molar volume of an ideal gas and R

H2

N2

CO2

Gas behavior creates the weather

• High atmospheric pressure pushes the atmosphere

• Low atmospheric pressure draw in atmosphere

• Pressure always tries to equalize

The troposphere contains pollutants

• Sulfur dioxide SO2

– Emitted from coal-burning power plants and industrial smelters• Particulate matter PM-10

– Particles with diameters less than or equal to 10 μm originating from agricultural tilling, construction, and unpaved roads.

• Carbon monoxide CO– Emitted from motor vehicles

• Ozone O3

– Formed by the action of sunlight on vehicle exhaust• Nitrogen dioxide NO2, Nitrogen oxides NOx (NO, NO2, NO3)

– Emitted from motor vehicles and electric utilities emissions• Lead Pb

– Emitted primarily from smelters and battery plants

Pollutants have adverse effects on life and environment• SO2

– Respiratory irritant and precursor to acid rain• PM-10

– Aggravates existing respiratory and cardiovascular disease, damage to lung tissue, and causes cancer

• CO– Diminishes the bloods ability to carry oxygen

• O3– Reduces lung function and prolonged exposure can

permanently damage lung tissue• NO2

– Brown color of smog and contributes to acid rain– Lung and eye irritant

• Pb vapor– Damages kidneys, liver, and nervous system.

The Clean Air Act

• A 1970 federal law regulating emissions

• Amendments passed in 1977 make regulation more

enforceable

• Overall pollution in urban areas is less even though there are

more vehicles.

• Vehicles today emit 60–80% fewer pollutants than those built

in the 1960s.

• Ground-level ozone is a persistent problem.

• Additional Clean Air Act amendments were passed in 1990.

CFCs are banned• industrial solvent, propellant• they linger in the stratosphere• UV causes photodecomposition and

reaction with ozone• Montreal protocol: phase out use

O3 + UV light O2 + O

CF2Cl2 + UV light Cl + CF2Cl

Cl + O3 ClO + O2

ClO + O O2 + Cl

atomic chlorine consumed

atomic chlorine regenerated

ozone destroyed

atomic chlorine produced