chapter 19 air pollution. core case study: when is a lichen like a canary? lichens can warn us of...

Chapter 19

Air Pollution

Core Case Study: When Is a Lichen Like a Canary?

Lichens can warn us of bad air because they absorb it as a source of nourishment.

Figure 19-1

Core Case Study: When Is a Lichen Like a Canary?

Some lichen species are sensitive to specific air-polluting chemicals.

After Chernobyl, more than 70,000 reindeer had to be killed because they ate highly radioactive lichens.

Because lichens are widespread, long-lived, and anchored in place, they can help track pollution to its source.

STRUCTURE AND SCIENCE OF THE ATMOSPHERE

The atmosphere consists of several layers with different temperatures, pressures, and compositions.

Figure 19-2

Fig. 19-2, p. 440

Atmospheric pressure (millibars)

Temperature

Thermosphere

Pressure

Mesopause

Heating via ozoneMesosphere

Stratopause

Alt

itu

de

(kil

om

eter

s)

Stratosphere Alt

itu

de

(mil

es)

Tropopause

Ozone “layer”

Heating from the earthTroposphere

Temperature (˚C)

Pressure = 1,000 millibars at ground level

(Sea level)

STRUCTURE OF THE ATMOSPHERE

Troposphere: innermost layer, decreasing temp, movement causes weather, contains 80% of air mass & 99% of H2O vapor

Stratosphere: increasing temp, Ozone filters out most of the sun’s UV radiation. Very stable, little mixing

Mesosphere: decreasing temp Thermosphere: outer most layer, increasing

temp (up to 1500oC) 2 sub layers: ionosphere-northern lights, exosphere- satellites

AIR POLLUTION

Some primary air pollutants may react with one another or with other chemicals in the air to form secondary air pollutants.

Figure 19-3

Fig. 19-3, p. 442

Primary Pollutants

CO CO2Secondary Pollutants

SO2 NO NO2

Most hydrocarbons SO3

Most suspended particles HNO3

H2O2 O3 PANs

Most NO3– and SO4

2– salts

Sources Natural Stationary

Mobile

H3SO4

• The activities of humans make a make a major contribution to global air pollution, but natural processes can also be responsible.

Lightning causes forest fires, oxidizes nitrogen, and creates ozone.

• Volcanic activity releases toxic, corrosive, & greenhouse gases. Volcanic particulates can also block out sunlight and contribute to global cooling.

Natural Processes

Causes of Air Pollution

Motor vehiclesHydrocarbons

HCNitric oxide NOCarbon monoxide

COSmoke and lead

IndustrySulfur doxide SO2

Nitrogen dioxide NO2

Carbon monoxide COHydrogen sulfide H2S

Dust, smoke

VolcanoesSulfur oxides

Carbon dioxideVolcanic dust

Photochemical smogIn the presence of direct sunlight,

the mixture of pollutants from primary sources reacts to form

ozone, nitric acid, PANs (peroxyacyl nitrates), and organic

compounds such as formaldehyde.

Petrol and diesel combustion engines

Emissions from power plants and industry, as well as burning fossil fuels

Volcanoes and forest fires are a natural source of air pollutants

Methane from the belching and flatus of ruminants

Major Air Pollutants

Carbon oxides: Carbon monoxide (CO) is a highly toxic gas that

forms during the incomplete combustion of carbon-containing materials.

93% of carbon dioxide (CO2) in the troposphere occurs as a result of the carbon cycle.

7% of CO2 in the troposphere occurs as a result of human activities (mostly burning fossil fuels).• It is not regulated as a pollutant under the U.S. Clean

Air Act.

Major Air Pollutants Nitrogen oxides and nitric acid:

Nitrogen oxide (NO) forms when nitrogen and oxygen gas in air react at the high-combustion temperatures in automobile engines and coal-burning plants. NO can also form from lightening and certain soil bacteria.• NO reacts with air to form NO2.

• NO2 reacts with water vapor in the air to form nitric acid (HNO3) and nitrate salts (NO3

-) which are components of acid deposition.

Nitrous oxide (N2O) is a greenhouse gas, from fertilizer, animal waste, & burning fossil fuel


Sulfur dioxide (SO2) and sulfuric acid: About one-third of SO2 in the troposphere occurs

naturally through the sulfur cycle. Two-thirds come from human sources, mostly

combustion (S+ O2 SO2) of sulfur-containing coal and from oil refining and smelting of sulfide ores.

SO2 in the atmosphere can be converted to sulfuric acid (H2SO4) and sulfate salts (SO4

2-) that return to earth as a component of acid deposition.


Suspended particulate matter (SPM): Consists of a variety of solid particles and liquid

droplets small and light enough to remain suspended in the air.

The most harmful forms of SPM are fine particles (PM-10, with an average diameter < 10 micrometers) and ultrafine particles (PM-2.5).

According to the EPA, SPM is responsible for about 60,000 premature deaths a year in the U.S.


Ozone (O3): Is a highly reactive gas that is a major

component of photochemical smog. It can

• Cause and aggravate respiratory illness.• Can aggravate heart disease.• Damage plants, rubber in tires, fabrics, and paints.

Major Air Pollutants Volatile organic compounds (VOCs):

Hydrocarbons emitted by the leaves of many plants Methane

• 1/3 natural sources: plants, wetlands, termites, anaerobic respiration

• 2/3 from human sources: landfills, oil & natural gas wells, cattle belching & flatulence, and rice paddies

Other VOCs: industrial solvents (trichlorethylene, benzene, vinyl chloride) and components of gasoline plastics, drugs, synthetic rubber.• Long-term exposure to benzene can cause cancer, blood

disorders, and immune system damage.


Radon (Rn): Is a naturally occurring radioactive gas found in

some types of soil and rock. It can seep into homes and buildings sitting

above such deposits. Causes lung cancer

URBAN OUTDOOR AIR POLLUTION

Industrial smog is a mixture of sulfur dioxide, droplets of sulfuric acid, and a variety of suspended solid particles emitted mostly by burning coal. In most developed countries where coal and

heavy oil is burned, industrial smog is not a problem due to reasonably good pollution control or with tall smokestacks that transfer the pollutant to rural areas.

Case Study: South Asia’s Massive Brown Cloud

A huge dark brown cloud of industrial smog, caused by coal-burning in countries such as China and India, stretches over much of southeastern Asia. In areas beneath the cloud, photosynthesis is

reduced interfering with crop development. Fine particles and droplets in the cloud appear to

be changing regional climates (including rainfall).• May have contributed to floods in 2002 and 2005

which killed thousands of people.

Sunlight plus Cars Equals Photochemical Smog

Photochemical smog is a mixture of air pollutants formed by the reaction of nitrogen oxides and volatile organic hydrocarbons under the influence of sunlight.

Sunlight plus Cars Equals Photochemical Smog

Mexico City is one of the many cities in sunny, warm, dry climates with many motor vehicles that suffer from photochemical smog.

Figure 19-4

Factors Influencing Levels of Outdoor Air Pollution

Outdoor air pollution can be reduced by: settling out, precipitation, sea spray, winds, and

chemical reactions. Outdoor air pollution can be increased by:

urban buildings (slow wind dispersal of pollutants), mountains (promote temperature inversions), and high temperatures (promote photochemical reactions).

Temperature Inversions

Cold, cloudy weather in a valley surrounded by mountains can trap air pollutants (left).

Areas with sunny climate, light winds, mountains on three sides and an ocean on the other (right) are susceptible to inversions.

Figure 19-5

Fig. 19-5, p. 447

Warmer air Descending warm air mass

Inversion layer Inversion layer

Sea breezeIncreasing altitude

Decreasing temperature

ACID DEPOSITION

Sulfur dioxides, nitrogen oxides, and particulates can react in the atmosphere to produce acidic chemicals that can travel long distances before returning to the earth’s surface. Tall smokestacks reduce local air pollution but

can increase regional air pollution.

ACID DEPOSITION

Acid deposition consists of rain, snow, dust, or gas with a pH lower than 5.6.

Figure 19-6

Fig. 19-6, p. 448

WindTransformation to sulfuric acid (H2SO4) and nitric acid (HNO3)

Windborne ammonia gas and particles of cultivated soil partially neutralize acids and form dry sulfate and nitrate salts

Wet acid depostion (droplets of H2SO4 and HNO3 dissolved in rain and snow)

Nitric oxide (NO)Sulfur dioxide (SO2) and NO

Dry acid deposition (sulfur dioxide gas and particles of sulfate and nitrate salts)

Acid fogFarm

OceanLakes in deep

soil high in limestone are

buffered

Lakes in shallow soil low in limestone

become acidic

ACID DEPOSITION

pH measurements in relation to major coal-burning and industrial plants.

Figure 19-7

ACID DEPOSITION

Acid deposition contributes to chronic respiratory disease can leach toxic metals (such as lead and

mercury) from soils and rocks into acidic lakes used as sources for drinking water.

ACID DEPOSITION

Acid deposition Damages statues, monuments, buildings Kills fish Harms crops & trees Is a regional problem downwind from coal-

burning facilities.

ACID DEPOSITION

Figure 19-8

ACID DEPOSITION

Air pollution is one of several interacting stresses that can damage, weaken, or kill trees and pollute surface and groundwater.

Figure 19-9

Fig. 19-9, p. 451

Emissions

SO2 NOxAcid deposition

H2O2 O3

Others

Direct damage to leaves & bark

Reduced photo-synthesis and growth

Susceptibility to drought, extreme cold, insects, mosses, & disease organisms

Soil acidification

Tree death

Leaching

of soil nutrients

Release of toxic metal ions

Root damage

Reduced nutrient & water uptakeAcids

Lake

Groundwater

PANs

Fig. 19-10, p. 452

Solutions

Acid Deposition

Prevention Cleanup

Reduce air pollution by improving energy efficiency

Add lime to neutralize acidified lakes

Reduce coal use

Add phosphate fertilizer to neutralize acidified lakes

Increase natural gas use

Increase use of renewable energy resources

Burn low-sulfur coal

Remove SO2 particulates & NOx from smokestack gases

Remove NOx from motor vehicular exhaust

Tax emissions of SO2

INDOOR AIR POLLUTION

Indoor air pollution usually is a greater threat to human health than outdoor air pollution.

According to the EPA, the four most dangerous indoor air pollutants in developed countries are: Tobacco smoke. Formaldehyde. Radioactive radon-222 gas. Very small fine and ultrafine particles.


Indoor air pollutants 2 – 5 times higher than outdoor levels

Source of cancer risk: 6000 deaths/yr Pesticide residue brought in on shoes Mold & mildew greatest cause of allergic

reactions Dust mite & coachroach droppings increase

asthma rates by 3x


Household dust mites that feed on human skin and dust, live in materials such as bedding and furniture fabrics. Can cause asthma

attacks and allergic reactions in some people.

Figure 19-12


Sick Building Syndrome (SBS) 1 in 5 commercial buildings considered “sick”

• When 20% or more report symptoms when inside the building and/or report relief of symptoms when outside

Exposes employees to health risks from unhealthy levels of indoor air pollutants

Dizzyness, headaches, coughing, shortness of breath, nausea, burning eyes, sore throats, respiratory infections, flu-like symptoms, skin irritation, chronic fatigue

Buildings at risk• Newer – formaldehyde & other VOCs offgasses, also

less gas exchange because more air-tight• Older – lead, asbestos, mold, mildew, poor ventilation,

temperature, & humidity control

Chloroform

Benzo-a-pyrene

Styrene

Radon-222

Methylene Chloride

Tobacco Smoke

Carbon Monoxide

Asbestos

Nitrogen Oxides

1, 1, 1-Trichloroethane

Particulates

FormaldehydeTetrachloroethylene

Para-dichlorobenzene

Fig. 19-11, p. 453

‣ Major indoor air pollutants:Radon is a radioactive gas that results from the decay of radium and uranium found in the bedrock under buildings. Responsible for tens of thousands of lung cancer deaths each year. Prevention: Remove radon by sealing or ventilating where radon enters the home.

Molds and allergens are caused by moisture induced growth of mold and mildew and the release of animal dander and plant pollen. Prevention: filtration, humidity and dust control methods

Carbon monoxide can be released from tobacco smoke, space heaters that use fossil fuel and wood burning stoves. Causes headaches and dizziness. Prevention: Proper ventilation

Indoor Air Pollution

Radon

Molds & Allergens

Carbon Monoxide

FormaldehydeAsbestos

Lead

‣ Major indoor air pollutants:VOCs like formaldehyde that can be associated with new building material like furniture and carpeting. Causes irritation of eyes, nose, throat and lungs Prevention: Ventilation or alternative materials

Asbestos fibers are present in floor or ceiling tiles and insulation materials of older buildings. Long term inhalation can lead to lung disease or mesothelioma. Prevention: Removal or sealing

Lead can be found in old plumbing pipes and fixtures, older paints, and some ceramic glazes. Causes impaired mental and physical development. Prevention: alternative paints or plumbing


Radon

Molds & Allergens

Carbon Monoxide

FormaldehydeAsbestos

Lead

Case Study: Radioactive Radon

Radon-222, a radioactive gas found in some soils and rocks, can seep into some houses and increase the risk of lung cancer.

Sources and paths of entry for indoor radon-222 gas.

Figure 19-13

Fig. 19-13, p. 454

Outlet vents for furnaces and dryers

Open window

Openings around pipes

Cracks in wall

Slab joints

Wood stove

Cracks in floorClothes

dryerSump pumpFurnace

Slab Radon-222 gas Uranium-238

Soil

HEALTH EFFECTS OF AIR POLLUTION

Your respiratory system can help protect you from air pollution, but some air pollutants can overcome these defenses. Figure 19-14

Fig. 19-14, p. 455

Epithelial cellCilia

Nasal cavity

Oral cavity

Goblet cell (secreting mucus)

Pharynx (throat)

MucusTrachea (windpipe)

BronchusBronchioles

Right lung

Bronchioles

Alveolar sac (sectioned)

Alveoli

Alveolar duct

HEALTH EFFECTS OF AIR POLLUTION

Normal human lungs (left) and the lungs of a person who died of emphysema (right).

Figure 19-15

Air Pollution is a Big Killer

Each year, air pollution prematurely kills about 3 million people, mostly from indoor air pollution in developing countries. In the U.S., the EPA estimates that annual deaths

related to indoor and outdoor air pollution range from 150,000 to 350,000.

According to the EPA, each year more than 125,000 Americans get cancer from breathing diesel fumes.

Air Pollution is a Big Killer

Spatial distribution of premature deaths from air pollution in the United States.

Figure 19-16

PREVENTING & REDUCING AIR POLLUTION

The Clean Air Acts in the United States have greatly reduced outdoor air pollution from six major pollutants: Carbon monoxide Nitrogen oxides Sulfur dioxides Suspended particulate matter (less than PM-10) Ozone Lead

‣ Major primary pollutants:Carbon monoxide (CO) is odorless and colorless poisonous gas emitted form the incomplete combustion of fossil fuels especially for transportation and combustion of waste. CO has a stronger affinity for hemoglobin than oxygen in the blood and can potentially cause suffocation. NAAQS criteria: Yes

Lead (Pb) is a product of leaded gasoline and comes out of the exhaust of cars and is also a product of metal smelting. Lead is a heavy metal that is toxic to nerve cells and can cause neurological damage. NAAQS criteria: Yes

Sulfur dioxide (SO2) is produced from industrial processes that burn fossil fuels like coal and petroleum. SO2 is implicated as a precursor to acid rain. Volcanoes are a non-anthropogenic source of SO2. SO2 reacts with the atmosphere to produce H2SO4 (sulfuric acid). NAAQS criteria: Yes

Primary Criteria Air Pollution

‣ Major pollutants:Nitrogen dioxide (NO2) is both primary and secondary and is emitted form high temperature combustion like power plants for energy production and automobile engines NO2 (N2+O2 NO2) Besides being a major component in photochemical smog, it can also lead to acid deposition. NAAQS criteria: Yes

Particulate matter (suspended particulate matter / spm) is both primary and secondary and consist of tiny particles, solid or liquid, suspended in a gas and are derived from soot and SO2 from coal burning. Dust from human activities and dust from storms, fires & volcanoes are other sources. Causes respiratory irritation. NAAQS criteria: Yes

Tropospheric ozone (O3) aka Ground level ozone is a secondary air pollutant that forms in a reaction with NO from motor vehicles, VOC’s, sunlight, heat and O2. Ozone in the troposphere damages plants and respiratory systems, traps heat and contributes to thermal inversions. NAAQS criteria: Yes

Criteria Air Pollution

2 SO2 + 2 H2O + O2 → 2 H2SO4

PREVENTING & REDUCING AIR POLLUTION

The EPA also established standards for 187 hazardous air pollutants (HAPs)

Cause serious health and ecological effects Chlorinated hydrocarbons Volatile Organic Compounds (VOCs)

• Benzene• Formaldehyde

Toxic metals

‣ Major air pollutants:Carbon dioxide (CO2) is a primary polluntant produced from the combustion of any organic material: gasoline, petroleum, coal, natural gas, biomass and also is a product of respiration. CO2 is a greenhouse gas that absorbs thermal radiation and re-emits the radiation at lower wavelengths.

Mercury (Hg) is a primary pollutant and the product of the combustion of coal. Mercury is a heavy metal that is toxic to nerve cells and is capable of bioaccumulation and biomagnification once fallout occurs and the Hg gets into water.

Nitrogen oxides (NO) is a prmary pollutant from transportation (cars, trucks, trains, boats & planes). High heat of engine causes O2 + N2 NO. Besides being poisonous NO reacts with O2 to form NO2, leading to ground-level ozone production.

Volatile organic compounds (VOCs) are both primary and secondary pollutants and are emitted from automobile exhaust, solvents, industrial processes, and household chemicals. These volatile chemicals contribute to climate change & ground level ozone. Some are carcinogenic (cancer causing) while some harm the respiratory system.

Non-Criteria Air Pollution

‣ Major air pollutants:Nitric acid (HNO3) is a secondary pollutant produced from reactions associated with transportation (cars, trucks, trains, boats and planes). NO2 + H2O NO + HNO3. Besides being a contributor to acid deposition nitric acid also harms respiratory systems and causes loss of soil fertility by leaching nutrients.

Peroxyacetyl nitrates (PANs) are secondary pollutants produced from reactions associated with transportation (cars, trucks, trains, boats and planes). NO2 + hydrocarbons (“HC”) PANs. PANs are a strong respiratory and eye irritant, can be potentially mutagenic and can damage vegetation by the inhibition of photosynthesis.

Sulfur trioxide (SO3) is a secondary pollutant produced from the combustion of coal and petroleum. (Coal has variable quantities of sulfur.) SO3 reacts with water in the atmosphere to form sulfuric acid (H2SO4) which contributes to acid deposition.

Sulfuric acid (H2SO4) is a secondary pollutant produced from the combustion of coal and petroleum. (Coal has variable quantities of sulfur.) H2SO4 contributes to acid deposition and harms respiratory systems and causes loss of soil fertility by leaching nutrients and possibly releasing toxic elemernts.

Secondary Air Pollutants

Air Quality is better in US; EPA estimates since 1970

Particulate Matter (PM) – down 78% Carbon Monoxide (CO) – down 56% Nitrogen Oxides (NOx) – down 30% Lead (Pb) – down 98% Sulfur Dioxide (SO2) – down 32%

Ground level Ozone (O3) – down 14% VOCs – down 55%

Air quality is worse in developing countries:

Mexico City & Beijing: air exceeds WHO standards 350 days/year

PREVENTING AND REDUCING AIR POLLUTION

Environmental scientists point out several deficiencies in the Clean Air Act: The U.S. continues to rely on cleanup rather than

prevention. The U.S. Congress has failed to increase fuel-

efficiency standards for automobiles. Regulation of emissions from motorcycles and

two-cycle engines remains inadequate. There is little or no regulation of air pollution from

oceangoing ships in American ports.


Airports are exempt from many air pollution regulations.

The Act does not regulate the greenhouse gas CO2.

The Act has failed to deal seriously with indoor air pollution.

There is a need for better enforcement of the Clean Air Act.


Executives of companies claim that correcting these deficiencies would cost too much, harm economic growth, and cost jobs.

Using the Marketplace to Reduce Outdoor Air Pollution

To help reduce SO2 emissions, the Clean Air Act authorized and emission trading (cap-and-trade) program. Enables the 110 most polluting power plants to

buy and sell SO2 pollution rights. Between 1990-2002, the emission trading system

reduced emissions. In 2002, the EPA reported the cap-and-trade

system produced less emission reductions than were projected.

Solutions: Reducing Outdoor Air Pollution

There are a of ways to prevent and control air pollution from coal-burning facilities. Electrostatic precipitator: are used to attract

negatively charged particles in a smokestack into a collector.

Wet scrubber: fine mists of water vapor trap particulates and convert them to a sludge that is collected and disposed of usually in a landfill.

Electrostatic Precipitator Can remove 99% of

particulate matter Does not remove

hazardous ultrafine particles.

Produces toxic dust that must be safely disposed of.

Uses large amounts of electricity

Figure 19-18

Fig. 19-18a, p. 460

Clean gas out

Negatively charged electrode

Positively charged precipitator wall

Dirty gas (smoke) in

Dust falls off into collector

Taken to landfill

Wet Scrubber

Can remove 98% of SO2 and larger particulate matter.

Not very effective in removing hazardous fine and ultrafine particles.

Figure 19-18

Fig. 19-18b, p. 460

Clean gas out

Separator

Liquid water in

Dirty gas (smoke) in

Polluted liquid (sludge) out

Catalytic Converter

installed on cars allow for more complete combustion of gasoline.

Fig. 19-17, p. 459

Solutions

Stationary Source Air Pollution

Prevention

Burn low-sulfur coal

Disperse emissions above thermal inversion layer with tall smokestacks

Remove sulfur from coal

Convert coal to a liquid or gaseous fuel

Remove pollutants after combustion

Shift to less polluting fuels

Tax each unit of pollution produced

Dispersion or Cleanup


In 2003, fourteen states and a number of U.S. cities sued the EPA to block new rules that would allow older coal-burning power plants to modernize without having to install the most advanced air pollution controls.


There are a of ways to prevent and control air pollution from motor vehicles. Because of the Clean Air Act, a new car today in

the U.S. emits 75% less pollution than did pre-1970 cars.

There is and increase in motor vehicle use in developing countries and many have no pollution control devices and burn leaded gasoline.

Fig. 19-19, p. 460

Solutions

Motor Vehicle Air Pollution

Prevention Cleanup

Emission control devices

Mass transit

Bicycles and walking

Less polluting engines

Less polluting fuels

Improve fuel efficiency

Car exhaust inspections twice a year

Get older, polluting cars off the road

Give buyers large tax write-offs or rebates for buying low-polluting, energy efficient vehicles

Stricter emission standards


Little effort has been devoted to reducing indoor air pollution even though it poses a much greater threat to human health than outdoor air pollution.

Environmental and health scientists call for us to focus on preventing air pollution (especially indoor) in developing countries.

Fig. 19-20, p. 461

Solutions


Prevention

Cover ceiling tiles & lining of AC ducts to prevent release of mineral fibers

Use adjustable fresh air vents for work spaces

Increase intake of outside airBan smoking or limit it to well ventilated areas

Change air more frequently

Set stricter formaldehyde emissions standards for carpet, furniture, and building materials

Circulate a building’s air through rooftop green houses

Prevent radon infiltration Use exhaust hoods for stoves and appliances burning natural gasUse office machines in well

ventilated areas

Use less polluting substitutes for harmful cleaning agents, paints, and other products

Install efficient chimneys for wood-burning stoves

Cleanup or Dilution

Fig. 19-21, p. 461

What Can You Do?


• Test for radon and formaldehyde inside your home and take corrective measures as needed.

• Do not buy furniture and other products containing formaldehyde.

• Remove your shoes before entering your house to reduce inputs of dust, lead, and pesticides.

• Test your house or workplace for asbestos fiber levels and for any crumbling asbestos materials if it was built before 1980.

• Don't live in a pre-1980 house without having its indoor air tested for asbestos and lead.

• Do not store gasoline, solvents, or other volatile hazardous chemicals inside a home or attached garage.

• If you smoke, do it outside or in a closed room vented to the outside.

• Make sure that wood-burning stoves, fireplaces, and kerosene- and gas-burning heaters are properly installed, vented, and maintained.

• Install carbon monoxide detectors in all sleeping areas.

Fig. 19-22, p. 462

Solutions

Air Pollution

Outdoor Indoor

Improve energy efficiency to reduce fossil fuel use

Reduce poverty

Rely more on lower-polluting natural gas

Distribute cheap & efficient cookstoves or solar cookers to poor families in developing countries

Rely more on renewable energy (especially solar cells, wind, & solar-produced hydrogen) Reduce or ban indoor

smoking

Transfer technologies for latest energy efficiency, renewable energy, & pollution prevention to developing countries

Develop simple and cheap tests for indoor pollutants such as particulates, radon, and formaldehyde

chapter 19 air pollution. core case study: when is a lichen like a canary? lichens can warn us of...

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