Air Pollution, Stratospheric Ozone Depletion, and Acid Deposition

 

I. Air Pollution

  • The Problem of air pollution is as old as civilization itself!!
  • Genesis (19:28): "Abraham beheld the smoke of the country go up as the smoke of a furnace"
  • Hippocrates (~400 B.C.): Noted the filth of the cities
  • An English Diarist (~1684): "the air in London was so filled with smoke that one could hardly see across the street"
  • Air pollution is most problematic in urban areas..... has increased markedly since the industrial revolution...  and is closely associated with cars, buses, and trucks


Natural Sourcesof Air Pollution

  • produce a greater quantity of pollutants than human-made sources
  • Volcanoes: SOx, particulates
  • Forest Fires: CO, CO2, NO2, particulates
  • Plants: HCs, pollens
  • Decaying Plants: CH4, hydrogen sulfide
  • Soil: dust and viruses
  • Ocean: salt spray and particulates

Anthropogenic (Human-Caused) Air Pollution
 
 

Important Anthropogenic Air Pollutants



 

*carbon monoxide (CO)

incomplete combustion of fuels

*nitrogen oxides(NOx)

high temperature combustion

*hydrocarbons HC

incomplete combustion of fuels

*ozone (O3)

photochemical reactions

*PAN

photochemical reactions

*sulfur oxides (SOx)

combustion of sulfur-containing fuels

particulates

dust, dirt, soot, salt, metals, organics

carbon dioxide (CO2)

complete combustion

water vapor 

combustion processes, steam

methane (CH4)

organic processes

* (denotes above that the pollutant results from combustion of fossil fuel - in transportation & at power plants & factories)
 

  • carbon monoxide - 70% from transportation
  • hydrocarbons - 60% from transportation
  • nitrogen oxides - 50% from transportation


                                
        Major "Primary" Pollutants and their Sources
 

"Primary Pollutants" -- are emitted directly from identifiable sources .  They pollute the air imediately after being emitted.

"Secondary Pollutants" -- are not emitted directly into the air, but form in the atmosphere when reactions take place among the primary pollutants.
 

A. Industrial Smog
 

"smog" = smoke + fog
 
 

industrial smog - contains: SOX, particulates, CO2 ....
 
 

sulfur dioxide:
 

  • results from combustion of fossil fuels, colorless, but pungent
  • impairs breathing - esp. breathing impaired individuals
  • can be transformed to sulfuric acid and sulfate aerosols
  • can be transported downwind to Canada
  • 70% of Canada’s SO2 originates in U.S.


 

B. Photochemical Smog
 
 

  • Results from the interaction of sunlight and combustion products of automobile exhaust

                        
        Photochemical Reactions
 
 

  • NOx and Hydrocarbons (HC)
  • assoc. with hazy sky and reduced sunlight in urban areas

(1) Nitrogen dioxide (NO2 )
 
 

  • reddish brown gas, damages and inflames respiratory systems
  • an ozone precursor

(2) Hydrocarbons (HC)
 
 

  • assoc. with the combustion of fossil fuels - automobiles and power plants/factories
  • an ozone precursor

(3) Ozone (O3)
 
 

  • affects the human respiratory system - (12 million children are at risk of developing health problems from ozone pollution)
  • damages plants (loblolly pine), reduces crop yields, weakens rubber and fabrics
  • forms as a secondary pollutant
  • NOx and HCs chemically react in the presence of sunlight to form ozone

NO2 + UV light > NO + O
 
 

O + O2 > O3
 
 

O3 + NO > NO2 + O2
 
 

build-up of ozone:
 
 

.....hydrocarbons are oxidized to peroxy radicals ... RO2....
 
 

RO2 + NO > NO2 +RO


 

II. Stratospheric Ozone
 

A.  Consequences of a Decrease in Stratospheric Ozone
 

  • an increase in the number of cases of skin cancer
  • an adverse impact on crops and animals due to an increase in energetic ultraviolet radiation
  • a cooling of the stratosphere that could affect stratospheric wind patterns, possibly inducing some form of climate change
  • for every 1% decrease in ozone, skin cancers increase by 5-10%
  • Ozone forms naturally in the stratosphere: molecular oxygen combines with atomic oxygen in the presence of another molecule
  • Ozone is destroyed naturally by absorbing UV radiation
  • Ozone is also destroyed by colliding with other gases, e.g., nitric oxide and nitrogen dioxide
  • Human activities are altering the amount of stratospheric ozone


                    
                    Total Ozone

CFCs:
 

  • Used as propellants in spray cans, refrigeration units, plastic foams for insulation, packing, furniture, solvents, and styrofoam containers
  • CFCs in aerosol cans have been banned in the US, Canada, Scandinavia since 1978, however, aerosol CFC production has increased overall in W. Europe as have worldwide nonaerosol CFCs
  • Once CFC molecules enter the middle stratosphere, ultraviolet radiation breaks them up, releasing chlorine in the process -- the chlorine then rapidly destroys ozone (one chlorine atom removes ~ 100,000 ozone molecules
  • The average lifetime of a CFC molecule is about 100 years


Stratospheric Ozone Depletion PPT


 

III. Acid Deposition
 
 

A. Introduction
 
 

  • Air pollution emitted from industrial areas, especially products of combustion, such as oxides of nitrogen (NOx), and oxides of sulfur (SOx) can be transported considerable distances downwind
  • These materials (gases and aerosols) either settle to the ground in dry form (dry deposition) or are removed from the air during the formation of cloud particles and are then carried to the ground in rain, snow, or fog (wet deposition).


B.  Formation of Acids
 

  • Emissions of sulfur dioxide and oxides of nitrogen may settle on the local landscape, where they transform to acids as they interact with water, especially during the formation of dew or frost
  • Airborne particles may transform into tiny dilute drops of sulfuric acid (H2SO4) and nitric acid (HNO3) during a complex series of chemical reactions involving sunlight, water vapor, and other gases.
  • These acid aerosols may then fall slowly to the Earth, or they may adhere to cloud droplets or fog droplets (acid fog)
  • They may even act as nuclei on which the cloud droplets begin to grow. When precipitation occurs in the cloud, it carries the acids to the ground

 

C. Occurrence and Extent of Acid Deposition
 

  • Precipitation is naturally somewhat acidic.  The carbon dioxide in the air dissolves in precipitation, making it slightly acidic with a pH between 5.0 and 5.6
  • However, precipitation is becoming increasingly acidic in many parts of the world, especially downwind of major industrial areas
  • Airborne studies conducted during the middle 1980s revealed that high concentrations of acid-rain producing pollutants can be carried great distances from their sources
  • In 1986, for example, scientists discovered high concentrations of pollutants hundreds of miles off the east coast of North America. It is suspected that they came form the industrial East Coast cities.
  • Acid rain knows no national boundaries!
  • Regions noticeably affected by acid deposition are: eastern North America, central Europe, and Scandinavia. Sweden contends that most of the emissions responsible for its acid precipitation come from factories in England.
  • In some cases, acid precipitation occurs naturally, e.g., northern Canada, where natural fires in coal beds produce tremendous quantities of sulfur dioxide
  • In the northeastern U.S., where emissions of sulfur dioxide are primarily responsible for the acid precipitation, typical pH values range between 4.0 and 4.5
  • Acid precipitation is not however confined to the northeastern U.S., the acidity of precipitation has increased rapidly during the past 20 years in the southeastern U.S. as well.
  • Further west, rainfall acidity appears to be on the increase as well. The main cause along the west coast for the increase in the acidity of rain, appears to be the oxides of nitrogen released in automobile exhaust
  • Some scientists feel that if the U.S. turns more to coal-fired plants, which are among the leading source of sulfur oxide emissions, the problem will worsen
  • To deal with the problem of acid deposition, the Clean Air Act of 1990 imposed a reduction in the United States emissions of sulfur dioxide and nitrogen dioxide.
  • Canada has recently imposed new pollution control standards and set a goal of reducing industrial air pollution by 50%

 

D. Effects of Acid Deposition
 

  • High concentrations of acid deposition can damage plants and water resources (freshwater ecosystems seem to be particularly sensitive to changes in acidity).
  • Concern centers mainly on areas where interactions with the soil are unable to neutralize the acidic inputs
  • Studies indicate that thousands of lakes in the United States and Canada are so acidified that entire fish populations may be adversely affected
  • In an attempt to reduce acidity, lime is being poured into some lakes
  • About a third of the trees in Germany show signs of a blight that is due in part to acid deposition
  • Apparently, acidic particles raining down on the forest floor for decades cause a chemical imbalance in the soil that, in turn, causes serious deficiencies in certain elements necessary for the tree's growth
  • Acid deposition is eroding the foundations of structures in many cities throughout the world.
  • In Rome, the acidity of rainfall is beginning to disfigure priceless outdoor fountain sculptures and statues
  • The estimated annual cost of this damage to building surfaces, monuments, and other structures is more than 2 billion dollars.