METEOROLOGY

GEL-1370

Chapter TwelveChapter Twelve

Air PollutionAir Pollution

What we are going to learn?

We are going to learn the answers to the following questions– What are the major sources of pollution?

– What are primary and secondary pollutants?

– Why does PM-10 pose the greatest risk to human health?

– Health problems associated with CO, SO2, VOCs, NOx?

– What is Smog? London-type and Los Angeles-type smog?

– Stratospheric vs tropospheric zone – which is beneficial?

– What is PSI scale?

– How does atmospheric stability influence the accumulation of air pollutants?

Historical Background of air pollution

• Major sources of pollutants: car exhaust, chimneys, power plants, factories, forest fires & other anthropogenic activities

• ~1/6th of world population in urban areas continuously exposed to health hazards from air pollutants

• Air pollution is as old as the invention of fire – smoke problem• King Edward I (1273): Declared a proclamation to stop using sea

coal, a dirty form of coal (soot and SO2)• 1850s: London had serious “pea-soup’ fog, a thick mixture of

smoke and fog that hung over the city• 1873: ~700 people died due to these fogs• 1911: ~1150 people in London died of smog (combination of

smoke and fog)• 1952: Major smog lasting for 5 days leading to 4000 people’s

death• 1956: Passage of ‘Clean Air Act’ in London

History of Air Pollution

• In US, industrial revolution brought air pollution

• By 1940s: Air in some cities was polluted that the auto-mobile headlights had to be turned on during the day

• 1948: Donora (PA), industrial pollutants got trapped in the Monongahela River valley, >20 people died, thousands became ill

• 1960s: Air pollution levels dangerously high in NY city

• In LA, heavy smog due to large petroleum-processing plants & automobiles; first alert toward the end of WW-II

• 1970: ‘Clean Air Act’ was passed; emission standards were set

• 1977, 1990: Clean Air Act was updated (stricter emission standards; incentives to encourage companies to lower emission standards)

• Amendments to the Act identified 189 toxic air pollutants

Easterly winds blow smoke from many large fires over a vast area of Southern Africa

Sources of Air pollutants• Air pollutants: Airborne substances, either solid, liquid, or

gases, that occur in high conc. Threatening the health of people, animals, vegetation and structures

• Natural Sources of pollutants: Dust and soot from earth’s surface (forest fires), volcanic eruption releasing tons of ash and dust into the atmosphere

• Anthropogenic Pollutants: – Fixed sources: Homes, office buildings, industrial complexes, power

plants, etc– Mobile sources: Motor vehicles, ships, jet aircraft, etc.

• Primary Pollutants: Enter atmosphere directly (from smokestacks and tail pipes)

• Secondary Pollutants: Formed when a chemical reaction occurs between a primary pollutant and some other component of air, such as water vapor or another pollutant

Some of the sources of Primary pollutants

• .Sources Pollutants

Natural Volcanic eruptions

Forest fires

Dust storm

Ocean waves

Vegetation

Hot springs

Particle (dust, ash), gases (SO2, CO2)

Smoke, unburned hydrocarbons (CO2, NOx, ash)

Suspended particulate matter

Salt particles

Hydrocarbons (VOCs), pollen

Sulfurous gases

Human caused

Industrial

Personal

Paper mills

Power Plants –coal oil

Refineries

Manufacturing-H2SO4

PO4 fertilizer

Iron & steel mills

Automobiles, fireplaces, home furnaces,

Particulate matter, sulfur oxides

Ash, sulfur oxides, nitrogen oxides

Sulfur oxides, nitrogen oxides, CO

Hydrocarbons, sulfur oxides, CO

SO2, SO3 and H2SO4

Particulate matter, gaseous fluoride

Gaseous resin

CO, NOx, VOCs, particulate matter

% of the primary pollutants in US

Primary sources of air pollutants in US

Denver (CO) on a clear day

Denver (CO) on a day when particulate matter and other pollutants reduce the visibility

Aerosols – suspended particulate matter• Aerosols: A group of solid particles and liquid droplets that remain

in suspension in the air; usually not poisonous; more substances include asbestos, fibers, arsenic, droplets of H2SO4, PCBs, oil, & pesticides

• Some particulate matter containing Pb, Ni, Cu, etc can affect respiratory system; make breathing difficult, particularly for those suffering from chronic respiratory disorders

• High accumulation of Pb in bones and soft tissues can cause brain damage, convulsion, and death; at low concentrations, dangerous to fetuses, infants and children when exposed may suffer central nervous system damage

• PM-10: Fine particulate matter < 10 m diameter

• > 10 m SPM settle in < 1-day; < 1 m remain in air for several weeks

Suspended particulate matter – contd.

• Total SPM emitted over US: 6.6 million tons; ~40% emitted from industrial processes; highway vehicles ~17%

• Arctic Haze: Sooty particles formed over the arctic during late winter and early spring

• These find SPM serves as nuclei for cloud droplets & ice crystals; when the particles are in 0.1-1.0 m size, haze particles effectively scatter incoming sunlight

• CO: A major pollutant of city air; odorless, poisonous gas formed during the incomplete combustion of carbon containing fuels; most abundant primary pollutant;

• Over 60 million metric tons/yr of CO enter the air in US; CO levels have decreased by ~40% since early 1970’s;

• CO is quickly removed from the atmosphere by microorganisms in the soil; human hemoglobin prefers CO to oxygen, so if CO is present, brain will starve of oxygen leading to headache, fatigue, drowsiness, and even death may result

SO2 & VOCs• Sulfur dioxide sources: burning of sulfur containing

fossil fuels (coal & oil); primary source includes power plants, heating devices, smelters, petroleum refineries & paper mills; volcanic eruptions and sulfate particles from ocean spray other major sources

• Inhalation of high concentrations aggravate respiratory problems, such as asthma, bronchitis & emphysema

• VOCs: Organic compounds that are mainly hydrocarbons – individual organic compounds composed of hydrogen and carbon; occur as solids, liquids and gases at room temperature

• Methane is the most abundant; Other VOCs include benzene, formaldehyde & some chlorofluorocarbons

VOCs & NOX

• 18 million metric tons of VOCS emitted into the air in US; 34% from vehicles used for transportation; ~50% from industrial processes

• Certain VOCs are carcinogens (cancer-causing agents) – benzene, benzo-a-pyrene (a product of burning wood, tobacco & barbecuing);

• Many VOCs are harmless, but combining with nitrogen oxides in the presence of sunlight to produce secondary pollutants that are harmful to human health

• NOX: Oxides of Nitrogen, primarily Nitrogen oxide (NO2) and Nitric Oxide (NO); forms when some of the nitrogen in the air reacts with oxygen during the high-temperature combustion of fuel

NOX & Ozone

• NOx are produced by natural bacteria; concentration in urban area is 10-100 times greater than nonurban areas

• In moist air, nitrogen dioxide reacts with water vapor to form nitric acid --- acid rain

• Sources of NOx: motor vehicles, power plants, and waste disposal systems

• Problems: Contribute to heart & lung problems, & lowering body’s resistance to respiratory infections; may encourage the spread of cancer; NOx are highly reactive gases & plays a key role in producing O3 in the air

• Ozone (O3): Noxious substance with unpleasant odor

• Smog means smoke + fog; used to refer smog that forms in large cities (e.g., LA)

Smog• Photo-chemical smog (or LA smog): Smog formed by

the chemical reactions in the presence of sunlight• London-type smog: When smog is composed of

sufurous and foggy air• Ozone forms naturally in the stratosphere through the

combination of molecular oxygen and atomic oxygen; stratospheric ozone provides a protective shield against sun’s harmful UV rays

• Tropospheric ozone: Near the surface, in polluted air, ozone is formed from a complex series of chemical reactions (with sunlight) involving pollutants, such as NOx and VOCs; normally higher during the afternoons and during the summer months

Ozone• Problems with ozone: Irritates eyes & mucous membranes

of the respiratory system, aggravating chronic diseases, such as asthma and bronchitis; exposure to low concentrations for 6-7 hrs during periods of moderate exercise can significantly reduce lung function; other symptoms include chest pain, nausea, coughing, and pulmonary congestion

• Ozone Production: Sunlight (< 410 nm) breaks down NO2 into NO and atomic oxygen– NO2 + Solar Radiation -------- NO + O

• O2 + O + M -------- O3 + M (M: third molecule)

• Ozone is destroyed by combining with nitric oxide

• O3 + NO ----------- NO2 + O2

Average (2-yrs, 6 cities) hourly concentrations of Ozone

Ozone – contd.

• Certain VOCs in polluted air allow ozone conc. to increase by preventing nitric oxide from destroying the ozone as rapidly as it forms

• VOCs react with oxygen and nitrogen dioxide to produce other desirable contaminants (such as peroxy-acetyl nitrate)--- harmful to vegetation & irritates eyes

• Ozone production should decrease in most areas when emissions of NOx and VOCs are reduced

• Ozone is most dense at ~25 km from earth surface; at this altitude, 12 ozone molecules/million air molecules (12 ppm)

• UV radiation < 300 nm has enough energy to cause cancer• Decrease of ozone in the upper atmosphere leads to the following:

a) Increase in the number of cases of skin cancer & eye cataracts and sun burning; b) suppression of human immune system; c) decrease in the ocean productivity & d) cooling of the stratosphere & changes in stratospheric wind pattern

Average distribution of ozone above the earth’s surface in the middle latitude

Ozone - contd

• Nitrous oxide from fertilizers & chlorofluorocarbons (CFCs) - drifting to the atmosphere through the breaks in the tropopause in the vicinity of jet streams & during thunderstorms penetrating into the lower stratosphere

• One single chlorine atom released from CFCs removes as many as 100,000 ozone molecules before it is removed by combining with other substances

• Average lifetime of a CFC molecule ~50-100 yrs• After 1987 Montreal Protocol, ~1% decrease in the total

concentrations of ozone destroying chlorine & bromine compounds

• >5 billion kg of CFCs have been released into the troposphere• Ozone layer thinned by ~3% during the summer from 1979-1991

over heavily populated areas of the Northern Hemisphere

Ozone molecule adsorbing UV radiation – dissociates into molecular and atomic oxygen

Ozone – contd.• Ozone levels dropped to record low levels over much of the globe –

mainly due to ozone-destroying chemicals and from the 1991 Mt.Pinatubo volcanic eruption (tons of sulfur dioxide gas into the atmosphere, formation of H2SO4)

• Ozone Hole: Sharp drop in the stratrospheric ozone level observed over the Antarctic during the spring

• Clean Air Act of 1970 – Since then, most of the pollutant levels have fallen off substantially; many amendments thereafter; 198 million autos on the road in a day

• Primary ambient air quality standards are set to protect human health and secondary standards to protect human welfare

• Nonattainment Areas: Areas that do not meet air quality standards (80 million Americans are breathing air that does not meet at least one of the standards)

Emission estimates of six pollutants in the US from 1940-1995

Pollutant Standard Index

• Pollutant Standards Index (PSI): Measure of air quality in a particular region; the highest value in one day is used; pollutant (CO, SO2, NO2, O3, SPM) measurement is converted to a number that ranges from 0 to 500;

• Pollutant value = primary ambient air quality standard, then, the pollutant is assigned PSI number 100; >100: unhealthful; 50-100: moderate; < 50: Good

• Total emissions of toxic chemicals spewed out into the skies over US declined steadily since EPA began the inventory of chemicals

Number of unhealthful days (by county) when PSI >100 (any of CO, SO2, NO2, O3 & SPM)

Factors that affect air pollution

• Role of wind: in diluting the pollutants• Most pollution occurs when the winds are light, skies

are clear, mixing is shallow, atmosphere is stable and a strong inversion exists

• Urban areas are more polluted than the rural areas• Urban areas tend to be warmer than urban areas• Acid rain is a major problem• Stability of atmosphere is determined by the way air

temperature changes with height

Smoke from the shorter stack is trapped within the inversion while smoke from taller

stack, above inversion, rises and mixes

Stability and Inversions

• An inversion (temp decreases slowly as we ascend or increases with height) represents extremely stable atmosphere where warm air lies over the cold air – lid on the vertical motion

• Pollutants from a shorter stack does not rise very high, but spreads out, contaminating the area while longer stacks release and the pollutants get mixed well and travel farther distances (dilution is the solution to the pollution!)

As vertical temp profile changes, the pattern of emitted smoke also changes

Inversion layer preventing the escape of pollutants

Thick layer of polluted air trapped in the valley

Cold air pollutants drain downhill and settle in the low-lying area

A weak country breeze carries pollutants from the outskirts into the city

pH Scale

Chapter Summary• Smoke in London, CA

• CO, NOx, SPM, how CO affect our body

• Volcano – source of what contaminant

• VOC, photochemical smog

• Primary and secondary pollutants

• Acid rain, pH of rain water

• Mixing depth

• PSI-scale

• Aerosols, VOCs, carcinogens, ozone, sulfur dioxide