Air Pollution and Biodiversity: Sources, Effects and Control

Historical industrial emissions, Birmingham, Alabama, May 1972. Photo: LeRoy Woodson, US EPA/DOCUMERICA, National Archives 545491; public-domain photograph via Wikimedia Commons. The visible plumes are not a chemical measurement.

Conservation and Biodiversity · Undergraduate biology and BS Botany

A leaf can be damaged by polluted air even when there is no visible smoke. These notes explain how airborne pollutants reach plants, soils and water, and why changes in those systems can reduce biodiversity. Start with the mechanisms, then use the worked example and assessments to test your understanding.

In this lesson

• What is air pollution?
• Primary and secondary pollutants
• How ozone damages plants
• Acid deposition: from air to soil and water
• Why extra nitrogen can reduce biodiversity
• Lead, carbon monoxide, CFCs and carbon dioxide
• BS-level assessment: concentration, deposition and risk
• A practical investigation and suitable controls
• How to write an evidence-based exam answer
• 20 revision MCQs
• 20-question interactive quiz

What is air pollution?

Air pollution is the presence of gases, particles or droplets in the atmosphere at concentrations and for durations that can harm organisms or the environment. A pollutant need not be visible. Clear-looking air can contain damaging ozone; a visible plume alone cannot identify its chemicals.

For conservation biology, follow the pathway from source → atmospheric transport or reaction → exposure → biological response. Pollution can injure a leaf directly or reach a plant indirectly after deposition changes its soil. Habitat degradation can then affect the insects, birds and other organisms that depend on that vegetation.

Learning goals: distinguish emissions from exposure, classify pollutants, explain four ecosystem damage pathways, interpret a critical-load calculation, and evaluate monitoring and control measures.

Primary and secondary pollutants

A primary pollutant is emitted directly, such as sulfur dioxide from sulfur-containing fuel or soot from combustion. A secondary pollutant forms through atmospheric reactions. Ground-level ozone is a key example: nitrogen oxides (NO_x) and volatile organic compounds (VOCs) participate in reactions driven by sunlight.

This classification describes how a pollutant reaches the air, rather than whether it is a gas or a particle. Nitrogen dioxide (NO₂) can be emitted directly and also form from oxidation of nitric oxide (NO). Particulate matter can likewise have primary and secondary origins.

Common pollutants: identity, source and ecological relevance

Pollutant	Typical sources or formation	Key point
SO2: sulfur dioxide	Burning sulfur-containing fuels; metal smelting	Contributes to acid deposition; emissions depend on fuel and controls.
NOx: principally NO and NO2	High-temperature combustion, including engines	Contributes to ozone formation, acid deposition and nitrogen inputs.
O3: ground-level ozone	Secondary formation involving NOx, VOCs and sunlight	Oxidant that damages sensitive vegetation.
PM: particulate matter	Combustion, dust and atmospheric particle formation	A mixture of suspended solid particles and liquid droplets.
NH3: ammonia	Livestock manure and fertilizer use	Direct vegetation effects and nitrogen enrichment.
Pb: lead	Metal processing and other lead-handling activities	Persistent contamination of soil and sediments after deposition.

PM₁₀ means particles with aerodynamic diameter generally ≤10 µm; PM_2.5 means fine particles generally ≤2.5 µm. These are size fractions, not chemical formulas; PM_2.5 is within the PM₁₀ fraction.

How ozone damages plants

Ozone can enter a leaf through its stomata. Reactions in leaf tissues generate oxidative stress, disrupting cellular processes and carbon assimilation. Sensitive plants may show reduced photosynthesis, growth or reproductive performance. Effects vary with species, exposure and growing conditions; injury is not always visible.

Compare two leaves exposed to the same outdoor ozone concentration. If stomatal opening differs, their absorbed doses may differ. Concentration outside the plant therefore does not completely describe the dose reaching its tissues. This links pollution biology to photosynthesis and the stomatal responses studied in plant water relations.

Ozone is location-dependent: ground-level ozone can injure vegetation, whereas stratospheric ozone absorbs much of the Sun's harmful ultraviolet radiation. The same molecular formula, O₃, has different environmental roles in different atmospheric layers.

Acid deposition: from air to soil and water

Atmospheric reactions involving SO₂ and NO_x can produce sulfuric and nitric acids. Wet deposition delivers dissolved substances in rain, snow or fog. Dry deposition delivers gases and particles without precipitation. “Acid rain” is the familiar term; acid deposition includes both routes.

Acid inputs can lower soil or water pH, promote loss of nutrient base cations and mobilize aluminum. These changes can impair roots and affect aquatic organisms. Sensitivity depends partly on geology and buffering capacity: two lakes receiving comparable inputs need not undergo the same pH change.

Normal rain is already mildly acidic because atmospheric CO₂ dissolves in water. Calling every rain sample below pH 7 “pollution-caused acid rain” is therefore incorrect. In an answer, connect acid-forming emissions → deposition → chemical change → biological effect, rather than simply saying that rain burns plants.

Why extra nitrogen can reduce biodiversity

Nitrogen is essential for growth, but excess atmospheric input can alter competition in habitats adapted to low nutrient supply. Fast-growing species may gain an advantage and shade smaller plants. The result can be greater vegetation biomass alongside lower plant diversity: productivity and biodiversity are different measurements.

Ammonia can affect foliage directly and, after deposition, contribute to nitrogen enrichment and soil chemical changes. Responses differ among lichens, mosses and vascular plants. Do not describe every nitrogen compound as equally harmful at every concentration.

Parmelia saxatilis, Black Hills, South Dakota, photographed 7 July 2011. Photo: Jason Hollinger, Wikimedia Commons, CC BY-SA 3.0; displayed without editing. This illustrates a lichen's form, not a diagnosed pollution injury.

Lichen communities can support biological monitoring, but interpretation requires species identification and environmental context. Tree-bark chemistry, moisture, light and habitat management can influence the observations. Some nitrogen-tolerant species may increase while sensitive species decline; total lichen cover alone can conceal that change.

Lead, carbon monoxide, CFCs and carbon dioxide

Lead: deposition can contaminate soil and sediment and affect plant and animal growth or reproduction. Leaded petrol for road vehicles was phased out globally by 2021, according to UNEP. That does not mean all airborne lead sources disappeared: metal processing remains relevant, and leaded fuel is still used by some piston-engine aircraft in the United States.

Carbon monoxide (CO): forms during incomplete combustion of carbon-containing fuel. Do not confuse it with carbon dioxide (CO₂) or describe it as a general product of “burning carbonates.”

Chlorofluorocarbons (CFCs): historically used in refrigeration, foams and some aerosol propellants, these stable compounds can reach the stratosphere. Ultraviolet radiation releases chlorine that catalytically destroys ozone. Production and use have been restricted under the Montreal Protocol; treating all modern aerosols or refrigerators as CFC sources is inaccurate.

CO₂: a natural atmospheric gas and photosynthetic substrate, but increasing its concentration strengthens greenhouse warming. Climate change can alter species ranges, seasonal timing and habitats. Dissolved excess CO₂ also contributes to ocean acidification. These mechanisms are distinct from ozone injury and sulfur/nitrogen acid deposition; naming the mechanism matters.

BS-level assessment: concentration, deposition and risk

Emission is the amount released at a source, commonly expressed as mass per time. Concentration is the amount in a volume of air, for example µg m⁻³. Deposition is transfer from the atmosphere to a surface. These quantities cannot be substituted for one another.

A critical level concerns atmospheric concentration above which adverse effects may occur according to current knowledge. A critical load concerns pollutant deposition, often expressed for nitrogen as kg N ha⁻¹ yr⁻¹. Values depend on the pollutant and sensitive habitat or receptor; there is no single universal ecological threshold.

Worked teaching example: suppose modeled nitrogen deposition is 12 kg N ha⁻¹ yr⁻¹ and the selected habitat critical load is 8 in the same units.
Exceedance = 12 − 8 = 4 kg N ha⁻¹ yr⁻¹.
The inputs are illustrative, not measurements from a named site or an official threshold. Positive exceedance indicates a concern for that habitat; it does not prove immediate death of every organism.

A practical investigation and suitable controls

Investigation: compare replicated sites along an exposure gradient with reasonably comparable habitat. Record pollutant measurements, dates, weather and vegetation composition. For a lichen survey, standardize the tree species and sampled trunk area, and identify species rather than recording only total cover. Include reference sites and acknowledge confounding variables.

Low-cost sensors can help teaching, but temperature, humidity, calibration, drift and pollutant interference can affect readings. Compare instruments under shared conditions before interpreting differences between sites. One cloudy-day reading or one damaged leaf cannot establish the cause of an ecosystem change.

Match pollution control to the source and pollutant

Problem	Approach	Reason
Combustion emissions	Reduce fuel demand and use cleaner energy; maintain appropriate emission controls	Prevent or reduce release at source.
Industrial particles	Fabric filters or electrostatic precipitators	Capture particles from exhaust; gas removal needs different controls.
SO2 in exhaust	Suitable flue-gas desulfurization or scrubbers	Remove acid-forming sulfur compounds.
NOx and VOC sources	Appropriate combustion, exhaust and solvent-emission controls	Address ozone precursors as part of coordinated air-quality management.
Agricultural NH3	Improve manure handling and fertilizer management	Reduce reactive nitrogen losses rather than adding more nitrogen to sensitive habitat.

Emission reduction and habitat management are complementary. Tree planting alone cannot replace pollution controls, and successful source reduction does not guarantee instant ecological recovery. Monitor both air quality and biological responses over time.

How to write an evidence-based exam answer

For “Explain how air pollution threatens biodiversity,” develop at least two complete causal pathways. For example: ground-level ozone uptake → oxidative stress → reduced plant performance → altered habitat resources; and excess nitrogen deposition → changed competition → loss of nutrient-sensitive species. Add a control matched to the pollutant and a monitoring method.

Distinguish observation (“species richness is lower at site A”) from interpretation (“nitrogen deposition may contribute”). Stronger explanations use measured exposure, comparable controls, replication and alternative explanations. Avoid unsupported statements that air pollution always destroys every species or is universally the greatest biodiversity threat.

Frequently asked questions

Can air pollution reduce biodiversity without killing plants immediately?

Yes. Changes in growth, reproduction or competition can alter species abundance over time. Sensitive species can lose ground while tolerant species persist. A community shift is an ecological effect even when there is no obvious mass mortality.

Is nitrogen pollution the same as a shortage of soil nutrients?

No. In a nutrient-poor habitat, excess nitrogen can favour particular competitors and change the community. The ecological response depends on habitat and dose; an element essential for plant growth can still cause problems when supplied in excess.

Why do ozone concentration and plant ozone dose differ?

Concentration describes the surrounding air; absorbed dose also depends on entry into the plant over time. Stomatal behaviour and growing conditions influence uptake, so equal outdoor concentrations need not produce equal tissue exposure.

Does a positive critical-load exceedance prove that a species has disappeared?

No. It is an indicator of ecological concern based on the selected habitat threshold and deposition estimate. Species loss requires biological evidence; interpretation should also consider uncertainty, other pressures and the time period.

Can lichen surveys replace chemical air monitoring?

They provide complementary biological information. Species identity, bark chemistry and microclimate affect interpretation. Combine a standardized survey with suitable exposure measurements rather than converting lichen cover directly into an exact concentration.

Are ozone depletion, acid deposition and climate change interchangeable?

No. Ozone depletion concerns loss of stratospheric UV protection; acid deposition concerns acid-forming substances reaching surfaces; greenhouse warming concerns the energy balance. They can interact with ecosystem pressures but require distinct explanations.

20 revision MCQs with explained answers

Choose one answer before opening the explanation. The interactive quiz below uses a different set of questions.

1. Which statement correctly defines a secondary pollutant?
   1. It forms through reactions in the atmosphere.
   2. It is any pollutant released by the second factory surveyed.
   3. It is always a liquid aerosol.
   4. It is any pollutant deposited after rainfall.
   Answer and explanation

   A. It forms through reactions in the atmosphere. — Secondary describes formation, not source order or physical state.

2. Which combination is central to ground-level ozone formation?
   1. Oxygen and limestone dust alone
   2. NOx, VOCs and sunlight
   3. Lead, nitrogen gas and darkness
   4. Carbon dioxide and rainfall alone
   Answer and explanation

   B. NOx, VOCs and sunlight — Ozone formation involves photochemistry with nitrogen oxides and volatile organic compounds.

3. Which description best fits particulate matter?
   1. Only particles visible to the naked eye
   2. Only material released directly by vehicles
   3. A mixture of suspended solid particles and liquid droplets
   4. A single gas with a fixed molecular formula
   Answer and explanation

   C. A mixture of suspended solid particles and liquid droplets — PM is a size-classified mixture and can include secondary particles.

4. What distinguishes PM2.5 from PM10?
   1. PM2.5 consists only of sulfur dioxide.
   2. PM10 cannot contain liquid droplets.
   3. PM2.5 means particles exactly 2.5 millimetres wide.
   4. PM2.5 is a smaller aerodynamic size fraction within PM10.
   Answer and explanation

   D. PM2.5 is a smaller aerodynamic size fraction within PM10. — The cutoffs are generally 2.5 and 10 micrometres, not millimetres.

5. What is an important route of ozone entry into leaves?
   1. Stomata
   2. Root hairs absorbing gaseous ozone from soil water only
   3. Pollen tubes conducting ozone from flowers
   4. Xylem transporting ozone directly from the stratosphere
   Answer and explanation

   A. Stomata — Stomatal uptake allows ozone to reach reactive sites in leaf tissues.

6. What does the absence of visible ozone injury establish?
   1. It establishes that photosynthesis increased.
   2. It does not rule out physiological damage.
   3. It proves that ozone uptake was zero.
   4. It proves that the plant is equally tolerant at all doses.
   Answer and explanation

   B. It does not rule out physiological damage. — Sensitive plants can lose performance without obvious injury symptoms.

7. Which pair contributes to sulfuric and nitric acid formation in air?
   1. Oxygen and molecular nitrogen alone
   2. Lead and sodium chloride alone
   3. SO2 and NOx
   4. Helium and argon
   Answer and explanation

   C. SO2 and NOx — Sulfur dioxide and nitrogen oxides participate in acid-forming atmospheric chemistry.

8. Which event illustrates dry deposition?
   1. Nitrate arriving in a rain droplet
   2. Dissolved acid arriving in snow
   3. Fog droplets depositing dissolved sulfate
   4. Particles settling on foliage without rain
   Answer and explanation

   D. Particles settling on foliage without rain — Dry deposition transfers gases or particles without precipitation.

9. Why can lakes respond differently to comparable acid inputs?
   1. Their catchments and waters can differ in buffering capacity.
   2. Every lake has the same geology.
   3. Acid inputs cannot change water chemistry.
   4. Lake area alone uniquely determines pH.
   Answer and explanation

   A. Their catchments and waters can differ in buffering capacity. — Geology and buffering help determine sensitivity to acidification.

10. Which outcome can follow excess nitrogen input to a nutrient-poor habitat?
    1. Every organism dies immediately.
    2. Fast-growing competitors increase while sensitive species decline.
    3. All species increase equally.
    4. Nitrogen ceases to be an essential nutrient.
    Answer and explanation

    B. Fast-growing competitors increase while sensitive species decline. — Nitrogen enrichment can change competition and community composition.

11. Which statement about nitrogen dioxide is correct?
    1. It is always a solid particle.
    2. It can never be emitted by combustion sources.
    3. It can have both direct emissions and secondary formation.
    4. It can only form inside a plant.
    Answer and explanation

    C. It can have both direct emissions and secondary formation. — Formation pathway matters: NO2 can be primary and secondary.

12. What does a critical load primarily describe?
    1. A gas concentration expressed only as volume per volume
    2. The total number of vehicles using a road
    3. The maximum number of species in a habitat
    4. A pollutant deposition quantity relevant to harmful ecological effects
    Answer and explanation

    D. A pollutant deposition quantity relevant to harmful ecological effects — Critical loads concern deposition; critical levels concern atmospheric concentration.

13. Which units suit an annual nitrogen critical load?
    1. kg N per hectare per year
    2. Micrometres of particle diameter
    3. Milligrams of nitrogen per litre of air only
    4. Degrees Celsius per minute
    Answer and explanation

    A. kg N per hectare per year — Deposition loading is expressed as mass per area per time.

14. Why are lichen observations interpreted cautiously?
    1. Bark chemistry never affects lichens.
    2. Species responses and habitat conditions can influence the pattern.
    3. All lichen species have identical pollution sensitivity.
    4. Lichens directly report every pollutant concentration.
    Answer and explanation

    B. Species responses and habitat conditions can influence the pattern. — Community composition can indicate stress but is not a stand-alone chemical measurement.

15. Which statement about leaded road petrol is current?
    1. Its phase-out eliminated every airborne lead source.
    2. It was first introduced worldwide in 2021.
    3. Its global phase-out was completed in 2021, while other lead sources remain.
    4. It remains the universal fuel for road vehicles.
    Answer and explanation

    C. Its global phase-out was completed in 2021, while other lead sources remain. — UNEP reported the end of leaded road petrol in 2021; metal processing and some aviation uses remain relevant.

16. What is the correct source description for carbon monoxide?
    1. Complete conversion of nitrogen to ammonia
    2. Photosynthetic splitting of water
    3. Deposition of inert argon gas
    4. Incomplete combustion of carbon-containing fuel
    Answer and explanation

    D. Incomplete combustion of carbon-containing fuel — CO formation is associated with incomplete combustion, distinct from CO2.

17. How do CFCs contribute to ozone depletion?
    1. They can release chlorine in the stratosphere under ultraviolet radiation.
    2. They remove all oxygen from the troposphere.
    3. They turn carbon dioxide directly into ozone.
    4. They act only by lowering rainfall pH.
    Answer and explanation

    A. They can release chlorine in the stratosphere under ultraviolet radiation. — Released chlorine participates in catalytic ozone destruction.

18. Which mechanism connects rising CO2 to climate change?
    1. Formation of lead particles in cloud droplets
    2. Enhanced absorption of outgoing infrared radiation
    3. Direct conversion of all atmospheric ozone into oxygen
    4. Removal of all nitrogen from air
    Answer and explanation

    B. Enhanced absorption of outgoing infrared radiation — Increasing greenhouse gases alters the planet's energy balance.

19. What does an electrostatic precipitator principally collect?
    1. Only ultraviolet radiation
    2. All dissolved nutrients in groundwater
    3. Particles in an exhaust stream
    4. All gaseous pollutants without distinction
    Answer and explanation

    C. Particles in an exhaust stream — Charged particles are attracted to collection surfaces; separate technologies address gases.

20. Which study design strengthens an ecological pollution investigation?
    1. One photograph with no site information
    2. One sensor reading with no calibration context
    3. Two different habitats sampled in different seasons without adjustment
    4. Replicated comparable sites with exposure measurements and relevant controls
    Answer and explanation

    D. Replicated comparable sites with exposure measurements and relevant controls — Replication and control of confounding variables make an explanation more defensible.

Interactive quiz: 20 new application questions

One correct option per question. Select your answers, check your score, then use the explanations to revise. Your answers stay in this browser; this quiz does not send them to a server.

1. A class measures deposition of 15 kg N/ha/year against an illustrative critical load of 9. What is the exceedance?

A. 6 kg N/ha/yearB. 24 kg N/ha/yearC. 1.67 micrograms/m3D. 9 kg N/ha/year

2. A report compares 20 micrograms/m3 with 8 kg N/ha/year. What must be corrected?

A. The comparison is valid because both contain nitrogen.B. The quantities use different dimensions and cannot be subtracted directly.C. The first number must be multiplied by the number of species.D. Both numbers must be treated as particle diameters.

3. Two seedlings have identical ambient ozone exposure but different stomatal opening. Which inference is justified?

A. The seedling with closed stomata must have higher ozone uptake.B. Stomatal behaviour is unrelated to gas entry.C. Their absorbed ozone doses may differ.D. Their tissue doses must be identical.

4. A rural woodland has elevated ozone despite few nearby factories. Which explanation should be investigated?

A. Proof that plants manufacture all measured ozoneB. Proof that the instrument measures only CO2C. The absence of any possible pollution sourceD. Transport of precursors or ozone and atmospheric formation

5. A student writes that all NO2 is secondary. What is the best correction?

A. Some NO2 is emitted directly, and some forms in air.B. All NO2 is primary, with no atmospheric formation.C. NO2 is not an air pollutant.D. NO2 is another name for PM2.5.

6. A 1-micrometre particle is identified in exhaust. Which size classification can include it?

A. Only particles greater than 10 micrometresB. Both PM2.5 and PM10C. PM10 but never PM2.5D. Neither fraction

7. Two ponds receive similar acid deposition, but one changes pH less. Which measurement would help explain this?

A. The age of the sampling notebookB. The colour of the sensor caseC. Buffering capacity and catchment geologyD. Only the number of passing vehicles

8. Rain has pH 6. A student calls this proof of industrial acid rain. What is the strongest response?

A. Every sample below pH 7 proves SO2 pollution.B. Rain cannot contain dissolved CO2.C. All rainfall naturally has pH 7 exactly.D. A below-neutral pH alone does not identify the source of acidity.

9. After nitrogen enrichment, total grass biomass rises but plant species richness falls. What follows?

A. Higher productivity does not necessarily mean higher biodiversity.B. The richness measurement must be impossible.C. Nitrogen has no influence on competition.D. Every ecological measure improved.

10. An observer records the same total lichen cover at two sites. What useful next step is missing?

A. Discard both observations because lichens never respond to pollution.B. Identify species and compare community composition and habitat.C. Assume identical air quality immediately.D. Convert cover percentage directly into ozone concentration.

11. A trunk survey compares different tree species in sun and shade. What most weakens the pollution inference?

A. Recording species namesB. Repeating counts in a defined areaC. Bark and microclimate differences are confounded with site exposure.D. Using more than one field notebook

12. Two identical low-cost sensors disagree after one was moved to humid conditions. What should the class do first?

A. Declare that the wetter site is definitely more polluted.B. Average readings without investigating the disagreement.C. Use the larger value as the official legal measurement.D. Check performance, humidity effects and calibration under shared conditions.

13. A factory installs a particle filter. Which claim still needs separate evidence?

A. That gaseous SO2 emissions have also been controlledB. That particles can be capturedC. That source controls can reduce emissionsD. That exhaust can contain a pollutant mixture

14. A city wants to reduce ozone injury in nearby crops. Which strategy addresses formation?

A. Treat ozone as a directly emitted metal dust.B. Manage NOx and VOC emissions using a coordinated assessment.C. Collect only fallen leaves after harvest.D. Remove atmospheric molecular nitrogen.

15. A photograph shows a white chimney plume. Which conclusion is defensible from the photograph alone?

A. The plume proves a particular PM2.5 concentration.B. The plume establishes the extinction of local lichens.C. A plume is visible, but its composition and concentration are undetermined.D. The plume must be pure sulfur dioxide.

16. A text claims modern road petrol is the dominant lead source everywhere. Which update is essential?

A. Replace lead with ozone without checking sources.B. State that airborne lead can no longer exist.C. Assume every aircraft uses the same fuel.D. Recognize the road-fuel phase-out and examine current local lead sources.

17. A student combines CFC ozone depletion and ground-level ozone injury into one mechanism. What distinction resolves this?

A. Stratospheric ozone loss and ground-level ozone exposure are different processes.B. Both are caused by ozone dissolving into roots only.C. Ground-level ozone is the layer that filters most UV radiation.D. CFCs are another name for nitrogen oxides.

18. A plant has yellow leaves near a road. What is a sound immediate interpretation?

A. The road must be the only possible cause.B. Pollution is one hypothesis; nutrient status, disease and water stress also need checking.C. The symptom uniquely identifies ozone.D. The symptom proves nitrogen deposition exceeded a critical load.

19. Annual deposition declines from 14 to 11 kg N/ha/year; an illustrative critical load is 8. Which statement is correct?

A. Deposition is now below the critical load.B. Every sensitive species must already have recovered.C. Exceedance fell from 6 to 3 but remains positive.D. Exceedance increased from 3 to 6.

20. Air-quality measurements improve after controls, but sensitive species return slowly. What is the best assessment?

A. The air-quality improvement must be false.B. The controls cannot have reduced emissions.C. All habitat management should end immediately.D. Monitor ecological recovery because exposure improvement does not guarantee immediate restoration.

Continue learning

• Biodiversity and its three levels — distinguish genetic, species and ecosystem diversity before studying their threats.
• Carbohydrates: structure and biological roles — connect photosynthetic carbon assimilation with the molecules plants produce.
• Water potential and plant water relations — connect water status with stomatal behaviour.
• Conservation and Biodiversity course — continue with habitat loss, overexploitation and other biodiversity pressures.

Sources and further reading

These independently written notes and teaching examples can be checked against the following scientific references.

• EPA: Ground-level ozone basics
• EPA: Ecosystem effects of ozone
• EPA: 2020 Integrated Science Assessment for Ozone
• EPA: Particulate matter basics
• EPA: What is acid rain?
• EPA: Effects of acid rain
• APIS: Ammonia and vegetation
• APIS: Lichens and bryophytes
• APIS: Critical loads and levels
• EPA: Lead air pollution
• UNEP: End of leaded petrol for road vehicles, 2021
• EPA: Ozone layer science
• EPA: Basics of climate change
• EPA: Climate change and ecosystems
• EPA: Pollution reduction strategies
• EPA: Electrostatic precipitators
• EPA: Air sensor limitations