Atmosphere & Air Pollution

Course Outline | Environmental Studies | EnvironmentalET

Atmosphere & Air Pollution

Atmosphere

Composition-see table
Evolution

in the distant past, earth like its sisters had an atmosphere of hydrogen
later volcanic activity released gases that formed an atmosphere of ammonia, methane, and water vapor

this is the atmosphere in which Oparin hypothesized that UV and electricity formed the precursor molecules to life

early life carried out the chemical reactions that produced the gases found today (nitrogen & oxygen)

2NH3 + 3CO2 ==> 3CH2O + N2
and the famous:
CO2 + H2O =sunlight=> CH2O + O2
(note: the oxygen comes from the water in photosynthesis)

Thermal profile

troposphere

up to ~40,000 ft
heated from below

temp decreases with altitude

stratosphere

85,000 to 165,000 ft
heated from above

O2 and O3 absorb UV light
temp increases with altitude

mesosphere

190,000 to 275,000 feet
heated from below (by earth and stratosphere

temp decreases with altitude, since rising air masses expand

thermosphere

320,000 on out
very low density
high rate of solar radiation (UV and cosmic rays)

temp increase with altitude (right off into space)
there's not much there but it's really moving (hence high temp)

Absorption & radiation

electromagnetic radiation

light, radio waves, xrays, microwaves etc are all part of the EM spectrum
frequency is proportional to the energy (E=hn ;
f = c/l = 1/n ) of each photon or particle of EM radiation
every object above 0 Kelvin radiates some of its heat as EM radiation called radiant energy; the hotter an object is the more energy it radiates

conversely, any object exposed to EM radiation can absorb some of the energy as heat
many nuclear reactions also generate EM radiation (primarily gamma rays) directly

the emission spectrum is a function of the substance and the temperature; the principle frequency is a function of temperature

in common speech we speak of things being red hot, blue hot or white hot: things which are white hot (like the filament of a light bulb) are hot enough to emit a full range of radiation in the visible spectrum; red light alone is not as high energy: red hot is not as hot as white hot

objects can also reflect some of the incident radiation: in general white reflects; black absorbs

perfect black is the perfect absorber/radiator
we calculate the "black body temperature" equivalent to a particular frequency

Radiation balance

sunlight

the sun is very hot, hence it radiates quite a bit
the structure of the sun is such that the photons leaving the 15 billion degree fusion furnace in the center of the sun take 10 million years to reach the surface, by which time the gamma rays and ultraviolet has been degraded to lots of visible light (the radiation the reaches the earth is mostly visible light)

Radiation balance and the greenhouse effect

chemical structure affects which wavelengths are most likely to be absorbed
chemicals have certain absorption maxima; for example:

water has an absorption maximum in the microwave region, hence microwaves are effective at heating water even though they are relatively low energy radiation
carbon dioxide has absorption maxima in the infrared
the spectrum of radiant energy from the earth contains mostly radiation in the infrared

this IR energy is radiated off into space unless reabsorbed by the atmosphere: carbon dioxide is a prime absorber

an increase in carbon dioxide level from 315 ppmv in 1958 to 344 ppmv in 1984 was recorded on the slope of Mauna Loa
based on this and other data the average annual increase in the second half of this century has been about 1½ ppm per year
sources of CO2 include:

burning fossil fuels

Note: burning coal produces nearly twice the CO2 of burning natural gas; why is that? Then again, using natural gas allows some methane leakage into the atmosphere

burning & rotting vegetation
deforestation and destruction of phytoplankton populations prevents reuptake of CO2 and hence fuels an increase in atmospheric content

other greenhouse gasses include methane, nitrous oxide and CFCs
there is no hard data connecting recorded temperature fluctuations and measured CO2 increases
CO2 has increased by as much as 20 percent since the beginning of the industrial revolution, but the actual increase has been only about one half of what would be predicted on the basis of fossil fuel burning etc
the greenhouse effect is theoretical and we do not possess the models to allow reliable calculations, there are many variables which we have not been able to account for

clouds both reflect incoming solar radiation and reabsorbs outgoing IR

how change in cloud cover due to warming would react is not known
a 1 percent increase in reflection by clouds would cancel out the predicted warming effect of CO2 at 600 ppmv!

the ocean has almost certainly acted as a carbon dioxide sink, its effectiveness is determined by ocean currents (which are only poorly understood)

the effect of warming on these currents could be to increase or decrease the ability of the ocean to absorb CO2

plants are being more productive with the increase in atmospheric carbon dioxide (as measured in tree rings)

may be the CO2 levels will stabilize under the influence of plants

CO2 is not the only greenhouse gas:

there are as many as 1500 lbs of termites per capita, mostly found in the tropics
termites thrive in recently razed forests
termites are estimated to produce 1/4 to 1/2 of atmospheric methane

if the overall pattern of the effects of warming form a negative feedback loop (ie if global CO2 or temperature homeostasis remains intact), we would not expect a runaway greenhouse

but there are factors that could have a positive feedback effect

methane ice under the oceans could melt causing a rapid increase in greenhouse gas
melted ice caps, reduced snow fall mean less solar reflection

the effects of global warming are also not certain, though we have some ideas:

EPA estimates that sea level will rise somewhere between 1 and 7 feet in the next 100 years, some folks estimate higher
melting of ice causes a steady rise, but the unstable West Antarctic ice sheet could rapidly break up and fall into the ocean causing a 15 to 20 foot rise in a matter of years or centuries
the mildening of northern winters could permit the spread of tropical diseases throughout the industrialized north
the temperature difference between the poles and the equator would decrease causing a decrease in the air flow patterns that bring rain to areas such as the midwestern US (the breadbasket)

Ozone

UV protection

in the conditions of chemistry and radiation in the stratosphere, oxygen forms ozone

ozone has a absorption maxima in the short wave UV, as well as xray and gamma rays
this radiation is only a few percent of the solar radiation reaching the stratosphere, but if it were to reach the ground it would be quite harmful to living things

Depletion

chlorofluorocarbons reaching the stratosphere catalyze the destruction of ozone
there is hard evidence that the ozone layer over the poles has been damaged
the estimates of overall ozone depletion, even at current levels of CFC release, predict sufficient loss to cause ground level health effects; if increase in CFC release is not prevented, serious effects may result

Climate-Human Effects

Cooling

dust causes a decrease in solar radiation reaching the surface of the earth
this is seen with volcanoes and forest fires (the ultimate would be the hypothetical nuclear winter)

Warming-discussed above
Heat Islands

building materials heat up in the sun; generation and use of electricity releases heat; combustion releases heat
cities are hotter than the countryside
this temperature difference can have an effect on air flow and the weather

increased fog or precipitation
pollutant plume sending junk downwind into the country
the bubble of hot air can act almost like a mountain that produces a stagnant weather system and a persistent urban haze

Cloud Seeding

silver iodide crystals are dispersed into clouds to provide nucleation sites for supercooled water vapor

the effectiveness and/or desirability of cloud seeding is a matter of some debate
holes can be punched in fog at airports and severe hail can sometimes be averted
some have argued for using cloud seeding to increase rainfall in agricultural areas or to de-fuse hurricanes

but not enough is known about overall rainfall patterns or the function of hurricanes for this to be clearly a good idea, even if it could be done (can you imagine the lawsuits?)

Air Circulation & Weather Patterns

The basic idea:

warm air rises and cool air rushes in to take its place

the land tends to heat up and cool off rapidly, the water more slowly

the ocean is cooler than the land during the day or in the summer, warmer at night or in the winter
two effects:

sea breezes (ie wind off the water) as the land warms up in the day and land breezes as the land cools off in the evening
the weather is more moderate along the shore

the oceans also carry heat from the tropics to the middle and higher latitudes, moderating the climates

Antarctica is colder than the arctic because it is surrounded by water; the ring of water allows a circumpolar current that blocks the warmer water from the lower latitudes

highs and lows

where warm air is rising there tends to be low pressure and where cool air is descending there tends to be high pressure

air wants to move from the areas of high pressure to low
because of the effects of the rotation of the atmosphere with the earth, the air rotates clockwise around or out of highs and counterclockwise around or into lows (in the northern hemisphere); this combination of pressure and rotational flow is called a high pressure or low pressure system (or anticyclone and cyclone)

cyclones associated with storms (including hurricanes & tornadoes) because water vapor condenses in the rising air; this process can lead to violent winds
anticyclones assoc with fair weather because the descending air tends to warm up and dry out, this process is not associated with violent winds

mountains

a mountain range can produce a cyclical wind pattern as well, either cool winds or warm (eg the Santa Ana winds)
mountains can also block the flow of moisture

as the moist air rises, it tends to dump its precipitation on the windward side
on the leeward side there is often a rain shadow or desert

or warm or cold air

the Himalayas separate a tropical region (India) from a near arctic (Siberia)

Warm & cold fronts

associated with rain

at a warm front, warm air climbs up over cold, is cooled as it rises and thus loses moisture as rain
at a cold front, cold air moves under warm, raising the warm, which cools as it rises....
and rain (stratiform) clouds:

cirrus
cirrostratus
altostratus
nimbostratus

Jet Stream

high altitude large scale winds, fast moving
regions of very high speeds are found where the air current narrows (jet maximums)

these are associated with strong fronts hence severe storms

Storms

Hurricanes

large amounts of latent heat are released by late season thunderstorms
the rising heated air leaves a low pressure area that surrounding air spirals in to fill
the air moving in is like a figure skater pulling in his or her arms to speed up: around the eye the wind is whistlin' (75 mph or more)
the inrushing air brings more moisture (ie more latent heat released as the air dumps its rain)
the storm is destructive due to high winds, high waves, lots of rain and a storm surge of water actually sucked up by the low atmospheric pressure

Tornadoes

smaller than a hurricane (several thousand times smaller in diameter) but incredibly vicious winds (450 mph or more)

the pressure can be low enough to cause buildings to explode

form when cool dry air cruises in over warm moist air

the warm air punches a chimney into the cold and the warm air rushes up the chimney (imagine water running out of the bathtub only upside down)
associated with thunderstorms
spawned at the edges of large hurricanes
not uncommon in Connecticut

Air Pollution

weather and air pollution interact

pollution can affect heating and cooling
temperature and wind can affect the distribution and mixing of pollutants
ordinary condensation was exacerbated by smoke causing the original London smog
sunlight and automobiles combine to form modern (LA) photochemical smog

Health effects

air pollution can be deadly in short order when concentrated by a temperature inversion: more than 4,000 people died in London in the autumn of 1952

four factors affect any given individuals response to a chemical or other agent, in the context of air pollution:

concentration: under normal conditions of horizontal and vertical mixing, pollutants do not become concentrated to toxic levels; but some conditions allow the toxins to accumulate

an inversion can occur when the air is still (analogous to the formation of a thermocline in a lake); when a bubble of warm air sits atop a layer of cool, there is no horizontal mixing; as in a lake, the lower layer becomes an isolated chemical system
(NOTE: its called an inversion, because normally the temperature decreases with altitude)
on open flat land, the effect of an inversion is not serious because the pollutants can still spread out horizontally by diffusion; if there are horizontal obstructions like mountains-LOOK OUT!

duration exposure: those present under or at the inversion will be exposed as long as the inversion lasts and they stay put

inversions caused by nightly cooling dissipate as the day warms up, but
inversions caused by fronts etc last as long as the weather

toxicity: varies with the toxin

expressed as an LD50: the dose which kills 50% of rats etc in experimental exposure
some toxins also have a threshold dose below which no toxic effects are seen:

Dose Response Curve

individual susceptibility: response to a given dose varies from person to person

age
pulmonary and cardiac health
allergies

the health effects of air pollutants are also mediated by a number of other factors:

synergy: a combination of toxins may multiply the toxic effects beyond the simple addition of expected dose responses; two or more toxins presented at less than threshold dose might have a toxic effect
physical state of the pollutant (gases vs particles)

gases freely enter the lungs fully
particles may be excluded from the lungs depending on size:

mucus and cilia in the nose and bronchiae exclude particles bigger than 10 microns
particles smaller than 1 micron can get trapped deep in the lungs
particles smaller than 0.01 microns behave essentially like molecules

different toxins affect different target organs

irritants and fibers have an acute or chronic effect directly on the lungs
some toxins (heavy metals, pesticides, organics) simply enter at the lung and subsequently damage the brain, liver, or other organs and systems
other toxins (particularly asbestos, radon, organics) can cause cancer

Other effects

dust and chemical pollutants (especially ozone) can cause deformation, reduced productivity and death in plants
particulate matter makes things grimy and sooty
acid from sulfur oxides rapidly dissolves marble and other stone and corrodes metal

Sources in the community

stationary point sources: smoke stacks, ventilation ducts
non-point sources or area sources: dust from construction and mining sites; emissions from a shopping center
mobile sources: cars, trucks

these continue to produce nearly intolerable levels of NMHCs, CO, NOx
formerly produced a tremendous burden of lead dust that remains on the roadsides (though levels of lead poisoning have abated since leaded gas was withdrawn)

Air pollution control standards

two different types:
- ambient standards (the NAAQSs) set maximum levels of the criteria pollutants in outdoor air for anywhere in the US
- emission standards regulate the amount of a pollutant that can be discharged from a particular source

Types of air pollution

suspended particulate matter

formerly TSP, now PM10 (particulate matter <10 microns)
typically produced by incomplete combustion (soot, smoke, mist) or by inorganic material mixed in with fuel (fly ash)
sources are power plants, industrial furnaces, boilers and similar stationary sources

coal is worse than oil, natural gas fired furnaces typically have no particulate emissions

fugitive dust from construction, manufacturing, foundries etc
four basic contol devices:

cyclone

relies on centrifugal acceleration to spin particulate matter to the walls of a round tube
cleaned air is emitted from the middle

baghouse

sort of like a giant vacuum cleaner or a fast sand filter (for water)
the dirty air is passed through a bank of fine mesh fabric bags
bags have to be cleaned periodically (usu by shaking)
effective down to submicron size
sensitive to high temperature and humidity or other vapors

wet scrubber

particles (and soluble gases) can be removed by streams of water
a spray tower is effective for larger particles
a venturi scrubber blasts high pressure streams of water across gas flowing through a venturi
essentially 100% effective against particles >5 µm
drawbacks:
produce a visible plume of water vapor
produce wastewater

electrostatic precipitator

widely used at power plants because they have the cheap and available juice
pipe or plate type: the particles are charged by a wire anode and migrate to a pipe or plate cathode
the buildup of dust makes the cathodes less effective
no moving parts (except that pipes must be banged to remove dust), require only electricity to operate but expensive

efficiencies:

Particle size (m m)	<1	5	25	100
Device	Removal efficiency (%)
Cyclone	25	65	92	97
Precipitator	50	89	99	100
Spray Tower	75	95	>99	100
Venturi Scrubber	88	100	100	100
Baghouse	93	100	100	100

other (gaseous) pollutants can also be controlled using scrubbers, or

absorption columns (AC etc)
incineration at about 1500°F
catalytic combustion at about 900°F

sulfur oxides (SOx)

of serious health concern; also responsible for acid precipitation
emitted mostly by power plants etc burning fuel (mostly coal, some oil) that contains sulfur
control schemes:

tall smoke stacks
change to low-sulfur fuel
remove the sulfur from coal before it is burned

inorganic sulfur (mostly pyrite) can be detergent-washed out of pulverized coal
organic sulfur can be solvent washed
or, the coal can be gassified or liquefied

sulfur can be removed from the flue gases

industrial emissions may have enough SOx to permit the economically feasible condensation of sulfuric acid (particulates must be removed first)
fossil fuel combustion gases can be desulfurized using lime or other dissolved neutralizing agents but solid sulfur waste disposal presents a thorny problem

carbon monoxide (CO)

an extremely toxic gas (reversibly destroys the oxygen carrying capacity of hemoglobin)
produced by incomplete combustion, primarily in automobile engines
catalytic converters complete the combustion of CO in the exhaust system
oxygenated fuels, with MTBE or ethanol added are required in some areas (including CT)

nitrogen oxides (NOx)

produced in automobile engines
react with HCs in the sunlight to form ozone and smog

sources of HCs include auto exhausts, fuel tanks, fueling, and fuel storage
HC controls include PCV devices, catalytic converters and other emission controls on cars; changes in fueling and fuel storage technology

NOx controls include changes in engine design and reduced auto use

lead

ambient standard set by EPA in response to a NRDC suit in the mid 70s

to achieve this standard (and to avoid poisoning catalytic converters), leaded gas had to be phased out (with observable reductions in blood lead as a result)

emergency controls: reduction or elimination of transportation or stationary source emissions (shut downs) can be required depending on the severity of pollution episodes

Trends in Community Air Quality

improvement with respect to SOx has been achieved in many areas by the control measures discussed
increasingly strict emission controls have reduced automobile pollution (CO, NMHCs)

but many areas (including CT) remain well above NAAQS
emission controls alone are not expect to be effective; thus other measures are being taken:

carpool lanes and other promos
commuter taxes on businesses
requirements for reduced or zero-emission-vehicles (natural gas or electric) and fleets

emissions of all the criteria pollutants was lower in the 80s than the 70s except for NOx (maybe because fuel efficiency sort of trades off for NOx production in autos)

hazardous air pollutants

the Clean Air Act empowers EPA to issue standards for pollutants that pose a health risk

standards have been issued or proposed for arsenic, asbestos, benzene, beryllium, mercury, radionuclides, and vinyl chloride and are under consideration for a number of other solvents, PAHs, and cadmium

indoor air pollution

problems with household air came to light following the energy efficiency needs of the 70s

household pollutants include combustion products, formaldehyde and other building material outgasses, cleaning products and other solvents, cigarette smoking, radon

ventilation regimes of large buildings must be properly designed, installed and maintained to provide adequate quantities of high quality air; improper ventilation can lead to the "sick building syndrome" which has reportedly been fatal (especially when you consider ventilation-related illness such as Legionaires Disease)

Acid Deposition

pH decreases in lakewater have been observed since the 1950s
acidification has destroyed fish life in hundreds of lakes in the northeast US (particularly upstate NY and northern NE) and southeast Canada (particularly Ontario); sulfur emissions from Great Britain have acidified lakes in Scandanavia; the eastern Great Lakes have been affected and the acidification of rainfall has been observed as far south as Texas and Florida
the acid is mostly due to the formation of sulfuric acid from SOx emissions, although some is due to NOx forming nitric acid
about 60% of SOx is from power plants, more than 30% from industrial combustion and other processes
rainwater has been measured with a pH as low as 1.5 (that would really sting your eyes or any cuts or scrapes)
the ecological effect is greatly buffered in areas that have limestone bedrock or soils and in lakes that have a high alkalinity; in areas like New England with granitic bedrock and soils, the ground is naturally acidic to start with and surface waters have a very low alkalinity
acid snow can have a drastic effect by causing a rapid drop in pH for a few days or weeks during the spring thaw
the controls discussed above for SOx can be effective against acid deposition, except that tall smokestacks just send the problem further downwind

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ANTHONY G BENOIT
ROOM 201B
(860) 885-2386

abenoit@trcc.commnet.edu