Air Pollution and its Impacts on Forests: Knowledge and Challenges Zhong Chen, Ph.D. Office of Academic Assessment Northern Arizona University Jiangsu.

Air Pollution and its Impacts on Forests: Knowledge and Challenges

Zhong Chen, Ph.D.

Office of Academic Assessment

Northern Arizona University

Jiangsu Institute of Botany

November, 2006

Outline

• Why this topic

• Air pollution-general

• Acid rain/deposition (SO2 and NOx)

• Ozone (O3) and UV-B

• Summary

Environmental Challenges in China• 16 of 20 most polluted cities in the world are located in China (World

Bank, 2006)• SO2 emission (a major source of acid rain) highest in the world• 2nd largest energy consumer in the world (next to US)• Severe Air, Water, and Soil pollution (close to Western Europe in 1960s)• ¾ urban population exposed to poor air quality (below national standard)• 300,000 premature death in China annually (WHO, 2002)• ¼ of world average in fresh water per capita (about 2,200 m3), limited

water resources but overused and highly polluted• Rapid urbanization increased traffic related air pollution and water

pollution• Land use change (particularly loss of wetland) and loss of biodiversity

Source: Frontiers in Ecology and the Environment, September 2006

Early Spring Sandstorm in Senyang, NE China, 2004

Pollutants• Primary pollutants: directly emitted into the

atmosphere through natural and human-related activities as gases, liquid or solid particles (aerosol); deposited onto surface by dry or wet (rain, fog, and hail) deposition

• Dry deposition involves diffusion (gases), Brownian motion (fine particles < 2.5 um in diameter), gravitational settling or sedimentation, and impaction (coarse particles > 2.5 um in diam.)

• Secondary pollutants: ozone (O3) and sulfate (SO4) particles through radiation and temperature

• Human (anthropogenic) activity: fossil combustion including transportation, and biomass burning (e.g. forest fires)

• Major natural processes: lightning, soil microbial processes, oxidation of ammonia

• Natural processes > human activity in the emission of methane (CH4), and carbon monoxide (CO) , both global warming gases

• Human activity > natural processes in global emission of sulfur dioxide (SO2) and oxides of nitrogen (NOx, NO+NO2)-two key pollutants

Sources of air pollution• Stationary -Point- emit air pollutants from one or more controllable

sites such as smokestacks of power plants -Fugitive-generate air pollutants from open areas

exposed to wind process such as dirty roads, construction sites, farmlands, storage piles, surface mines

-Area-emission from a well-defined area and several sources such as small urban community and intense industrialization within urban complex or spray herbicide and pesticide on agricultural areas

• Mobile – automobiles, trucks, buses, aircrafts, ships, trains

The Kaiser Aluminum Plant smokestack, behind the Catholic church, belches fumes over the residential area in the Chalmette section, 1973

Pollution from the Jones and Laughlin Steel Corp. at Aliquippa, PA, near Pittsburgh. Some discharge also is made into the Ohio River. The pollution has continued since this picture was taken. Some controlled improvements have been made and additional cleanup efforts have been scheduled, 1973. U.S. National Records Archive.

(China’s Environmental Pollution, National Geographic, March 2004)

Categories of pollutants• Infectious agents (environmentally transmitted infectious

diseases via water, air, soil and food)• Toxic heavy metals (mercury, lead, cadmium, nickel, gold,

silver, arsenic, selenium, vanadium, chromium…)• Organic compounds• Radiation (nuclear radiation)• Thermal pollution (electric power plants)• Particulates• Asbestos (small, elongated mineral fragments/fibers)• Noise pollution• Electromagnetic fields (electric transmission lines for

utilities and appliances)• Light pollution (urban areas particularly)

• Sulfur dioxide (SO2)• Nitrogen oxides (NOx)• Carbon monoxide (CO)• Photochemical oxidants (ozone, O3)• Hydrocarbons• Hydrogen sulfide (H2S)• Hydrogen fluoride (HF)• Other hazardous gases• Particulate matter (PM)• Asbestos and lead

Major air pollutants

• Sulfur dioxide (SO2): 1) major sources- burning of fossil fuels (e.g. power plants), and industrial processes (petroleum refinery, cement, aluminum, and paper); 2) may be converted to fine particulate sulfate (SO4) through complex reactions; 3) directly results in injury to death of plants and animals, severe damage to respiratory system, precursor of acid rain

• Nitrogen oxides (NOx, NO and NO2): 1) nearly all NO2 emitted from anthropogenic sources (automobiles and power plants); 2) converted to ion (NO3 –2) within small water particules, impairing visibility; 3) smog, acid rain; 4) human respiratory diseases including influenza (lead to bronchitis and pneumonia); 5) nitrogen fertilization

• Carbon monoxide (CO): 1) sources- 90% from natural process (oxidation of natural hydrocarbons, microbial activity in oceans, emissions from plants), 10%-fires, automobiles, incomplete burning of organic compounds); 2) extremely toxic to humans (heart disease, anemia, respiratory diseases) and animals

• Photochemical oxidants (PAN (peroxyacyl nitrates) and ozone (O3); 1) sources- human activity (automobile, fossil fuel burning, and industry-produce nitrogen oxides); 2) photochemical smog; 3) hazardous gases to people (eyes and respiratory system); 4) very active chemically, short average life time of cells

• Hydrocarbons (CxHy): 1) sources- 80+% from natural process (oxidation of natural hydrocarbons, microbial activity in oceans, emissions from plants), 10%-fires, automobiles; 2) methane (CH4), butane (C4H10), and propane (C3H8)- greenhouse gases; 3) numerous adverse effects to people, plants, and animals through chemical changes

• Hydrogen sulfide (H2S) and Hydrogen fluoride (HF): 1) sources- H2S mainly natural process, and HF industry (power plant); 2) both high toxic and corrosive; 3) hazardous gases to people, plants and animals

• Particulate matter (PM): 1) construction project-smoke, soot, dust; airborne asbestos; small particles of heavy metals-copper, lead (automobile battery and gasoline) , zinc from industrial facilities; 2) most significant of fine particulate sulfate and nitrates-converted to secondary pollutants (SO4 and NOx)-acid rain; 3) affect human health, ecosystems, and biosphere greenhouse gases (block sunlight may cause changes in climate) gases to people, plants and animals

Trace gases Sources Present con. (ppb)

Greenhouse effects, %

CO2 Fossil fuels,

deforestation

353,000 60

CO Fossil fuels,

Biomass burning

100 0

CFCs Refrigerants, aerosols, industrial process

0.28-0.48 12

CH4 Rice culture, cattle, fossil burning, biomass burning

1,720 15

N2O Fertilizer; land use conversion

310 5

Tropospheric ozone (O3)

Hydrocarbons (with NOX), biomass burning

25-45 8

H2O Land conversion, irrigation

3,000-6,000 unknown

Atmospheric trace gases that are radiatively active and of significance to global change (EarthQuest 1990)

Principal natural sources not included

London Smog

In December 1952, air in London became stagnant and cloud over blocked solar radiation

Thick fog developed (30F, 80% humidity)

Home heating (coal burning-emission of ash, SO2, soot, smoke) + Automobile exhausts

About 4,000 people died between Dec. 4-10, 1952

Weather changed and pollution disappeared.

Photochemical smog ------arises mainly from the combustion process by motor vehicles, as well as the increased use of fossil fuels for heating, industry, and transportation. These activities, along with slashing-and-burning of trees and agricultural organic wastes, led to large emissions of two major primary pollutants, volatile organic compounds (VOCs) and nitrogen oxides. Interacting with sunlight, primary pollutants form various hazardous chemicals known as secondary pollutants-namely peroxyacetyl nitrates (PAN) and ground-level (tropospheric) ozone.

Sulfur dioxide[SO2]

Ozone[O3]

NO2

Peroxyacetyl nitrate(PAN)

CH3-CO-ONO2

OAir:

Nitrogen 78%

Oxygen 21%

CO2 0.03%

Fuel:

Hydrocarbons

Sulfur contaminant 1-6%

Additives (tetraethyllead)

Combustion, heat, and pressure

Unburned hydrocarbons

Lead (particulate)

CO2 and CONO UV light

UV light

O2

[O]

Plant-pathogenic air pollution resulting from the combustion of fossil fuels (Manion 1991)

NOx

OrganicCompounds

Hydrocarbons

Concentrated photochemical smog (brown air)

+

Solar radiation

With presence of an inversion layer, trapping pollutants

Burning coal or oil in an urban area

Sulfur oxides (SOx)+Particulates

With stagnant, stable air sufficient relative humidity, cloud cover, and formation of inversion layer and thick fog, lasting several days

Concentrated sulfurous smog (gray air)

Acid rain/deposition• Acid rain encompasses both wet (rain, snow, fog)

and dry (particulate) acid deposition that occur near and downwind of areas where major emissions of SO2 and NOx result from burning fossil fuels, pH (1.5-5.6 (“pure rain”))

• Examples of damages: 1) death of thousands of acres of conifer trees in Bavaria, Germany; half of red spruce in Vermont; 2) death of fish in lake ecosystems; 3) human society-steel, paint, masonry, buildings , and considerable health hazards

1) Major sources- burning of fossil fuels (e.g. power plants), and industrial processes (petroleum refinery, cement, aluminum, and paper)

2) May be converted to fine particulate sulfate (SO4) through complex reactions

3) Precursor of acid rain/deposition

4) Directly results in injury to death of plants and animals, severe damage to respiratory system

Sulfur dioxide (SO2)

SO2 pollution facts• Almost all from fuel burning (electronic power

plants), about 20 times natural sulfur emission, unprecedented in geological records

• Acid rain, and forming small aerosols with other particulates and moisture

• As an environmental threat, since at least 18th century, deleterious effects to lakes, forests, soils etc. have been scientifically documented for at least 30 years

• Long-term impacts—predispose trees succumb to insects, diseases, drought, and nutrient stresses

http://telstar.ote.cmu.edu/environ/m3/s4/cycleSulfur.shtml

Nitrogen oxides (NOx, NO and NO2)

1) Nearly all NO2 emitted from anthropogenic sources (automobiles and power plants)

2) Converted to ion (NO3 –2) within small water particules, impairing visibility

3) Smog, acid rain/deposition

4) Human respiratory diseases including influenza (lead to bronchitis and pneumonia)

5) Nitrogen fertilization

Global budget for the oxides of nitrogen, NOx (NO + NO2)

Sources Nitrogen (1012 g/year)

Fossil fuel combustion 21 (14-28)

Biomass burning 12 (4-24)

Lightning 8 (2-20)

Microbial activity in soils 8 (4-16)

Oxidation of ammonia 1-10

Biological processes in the ocean > 1

Input from the stratosphere About 0.5

Total 25-99

http://www.physicalgeography.net/fundamentals/9s.html

Acid neutralizing capacity• Great acid deposition results in increased leaching

of base cations (e.g. Ca 2+ , Mg 2+ , K+, Na+) through

acid neutralizing reactions in the soil • Release of base cations: 1) mineral weathering of

rocks; 2) cation exchange in soils (e.g. hydrogen ions H+ replaced other cations)

• Cation depletion is a cause for concern because of the roles in acid neutralization and importance as essential nutrients

• Depletion of base cation and increase aluminum mobilization cause mortality of sugar maples in west and central Pennsylvania

N deposition- too much a good thing

• Increased mobile aluminum (Al), which will be toxic to root systems, meaning decreasing symbiotic mycorrhizae fungi and loss of fine root biomass

• Reduced ability of taking up water and tolerant to water stresses

• Leaching out essential nutrients (Ca, Mg, and K) and decrease tree growth

Acid deposition variations• Elevation : greater amount of deposition in higher

elevation than in lower elevation, may not hold true for areas that close to a significant source of air pollution (e.g. close to LA metropolitan areas)

• Regions: 1) NE soil developed in most recent glaciations has less ability to absorb sulfate in soil, tend to surface water acidification; 2) SE older non-glacial soils higher capability of absorbing sulfate, surface water acidification does occur; 3) western region in US, California-high N deposition but soil has higher base saturation

• Land use: 1) harvesting may deplete soil pools of mineral nutrients-resulting in lower buffering capacity of soil-more susceptible to acid deposition; 2) fires, particularly in severely fire disturbed areas-retain nitrogen deposition for extended period of time

• Ecosystem response to acid deposition is nonlinear and case specific!

Acid deposition variations (cont’d)

Pollution-related forest declines of the past 50 years

• Widely assumed major role -Massive die-off forests in Europe

(Waldsterben) -Decline of ponderosa pine and

Jeffery pine in the San Bernardino Mts. of California

-Regional decline of white pine in the eastern US and Canada

• Possible major role -Decline of red spruce, Balsam and Frasser

firs at high elevation in the Appalachian Mts from Georgia to New England

-Growth decline without other visible symptoms in loblolly, short leaf, and slash pines in the Piedmont regions of Alabama, Georgia and Carolinas

-Widespread dieback of sugar maples in northeastern US and SE Canada

Pollution-related forest declines of the past 50 years (cont’d)

Pollution-related forest declines of the past 50 years (cont’d)

• Declines related to biological or physical factors - Decline of oaks in Germany and France since

early 1900s - Birch, ash dieback in northeastern US and

SE Canada - Maple decline in northeastern US and SE

Canada - Littleleaf disease of shortleaf pine in SE US - Oak decline in PA, VA, and TX

Recovery of ecosystems from acidification depends on

• The amount of acid deposition (nitrogen and sulfur oxides)

• Contribution of natural acidity

• Sub-lethal level chronic effects

• Depletion of exchangeable base cations (Ca

++, Mg++, Na

+, K+)

Patterns of major air pollutant change worldwide and impacts on forest ecosystems

(Karnosky et al. 2003)

Pollutant Distribution and change Impacts

CO2 Increasing globally Short-term growth and productivity increase; long-term effects uncertain

O3 Global increases in O3 and its precursors with largest increase from developing countries

Growth and yield loss to sensitive species; predisposition to insects and diseases

Nitrogen Global increase, particularly in developing countries

Stimulating growth in N-poor soils, contribution to increase ozone, negative effects from nitrogen saturation

Sulfur Decrease in the past few decades in developed countries but increase in developing countries, stable globally

Acidification in soils in many parts of the world and difficult to mitigate

S monitoring and research needs• Monitoring

-1) S deposition in countries in transition and in developing countries; 2) continued assessments of impacted forest ecosystems to ensure proper restoration

• Forest research

-1) methods to mitigate long-term sulfur inputs into soils and to restore sustainable forest ecosystems; 2) effects of S deposition on forest ecosystems, particularly in developing countries

N monitoring and research needs• Monitoring -1) N deposition in countries with rapidly

expanding automobile traffic and industry; 2) long-term monitoring of acidification of streams, ponds, and lakes; 3) long-distance transportation and contribution to O3 formation

• Forest research -1) Effects of N additions in N-saturated or

nearly N-saturated ecosystems; 2) effects of N deposition to ecosystems experiencing other pollutants; 3) effectiveness of various N mitigation treatments on forest soils and watersheds

Ozone is a molecule that contains three atoms of oxygen and thus has the formula O3; Ozone was first discovered in 1839 by German scientist Christian Friedrich Schonbein.

(Source: http://www.theozonehole.com/ozone.htm)

Layers of the Earth's atmosphere

NOAA Graphic

(Sources: http://www.theozonehole.com/ozone.htm)

Ozone Precursors

• Seasonal: summer highest, related to temperature and UV radiation

• Diurnal: 1) far from urban areas- concentrations are low in early morning and increase only slightly during mid-afternoon; 2) rural with urban influence-concentrations are low in early morning, increase during the afternoon, and decline at night; 3) urban areas-concentration rise beginning at sunrise, peak by early afternoon and then decrease

Patterns of ozone exposure

Patterns of ozone exposure

Concentrations in the US

-average 20-60 ppb over most of the US; average 6-80 ppb in urban areas of California; much higher levels can occur over several hours or days; O3 in Flagstaff 1980-88 was 44 ppb, but 60+ ppb for 14% of all hours; S. California 1-hr peaks above 200 ppb are common; day time average 50 ppb in forest areas in summer

Examples of ozone damage

• Mixed conifer forests of S. California-Ponderosa pine and Jeffery pine forest in the San Gabriel and San Bernardino Mts. Began showing symptoms of foliage damages in the early 1950s, subsequent controlled experiments confirmed ozone as a causal agent (McLaughin and Pearcy 1999)

• Eastern white pine (P. strobus)-needle “blight” (tipburn, chlorosis, necrosis) symptoms appeared about 70 years ago in parts of Appalachian Mts. and NE, experiments between 1960-70 confirmed ozone damage

• Eastern hardwoods and conifers in S. Appalachian Mts.• Current damage crops and forest trees at ambient

concentrations on a regional level in N. America

Physiological effects of ozone on forest trees

• Increased production of antioxidant compounds-defense mechanisms, but requires energy normally devoted to support other processes

• Decreased net photosynthesis-damage chloroplast membranes

• Increased dark respirations-repair of damaged membranes or the production of antioxidant compounds

• Decreased stomatal sensitivity to water stress-predispose trees to water stress

• Decreased leaf longevity-premature senescence

Physiological effects of ozone on forest trees (continued)

• Altered carbohydrate fractions-foliar starch typically reduced and sugar concentration increased perhaps due to disruption of carbohydrate sink-source relationships

• Increased turnover of N in young foliage-may drain the energy pool

• Decreased wood density and tracheid length-based on limited study with Populus and several eastern conifers, may due to changes of carbon allocation toward repair or replacement of damaged foliage

Physiological effects of ozone on forest trees (continued)

• Increase shoot-to-root ratio: exposure to ozone typically reduced root growth more than shoot growth- this may be a consequence of changes in carbon allocation towards repair or replacement of damaged foliage; this further may increase susceptibility of trees to drought by decreasing capacity for water uptake

• Decreased root carbohydrate concentration: seedlings typically decreased storage of carbohydrates in dormancy

• Decreased carbon allocation to mycorrhizae (Andersen and Rygiewicz 1995)

• Distinct visible discoloration in western conifer needles – chlorotic mottle typically occurs on needle surface (Miller et al. 1962)

• Chlorotic mottle- 1) needle tip and necrosis, progress basipetally; 2) needle abscission; 3) old whorls of needles dropped (4-1); 4) crown death (upward) (Miller 1977)

• Sensitive species: Ponderosa pine, Jeffery pine, and White fir (A. concolor)

Assessing O3 injury

Susceptibility to ozone

• Inter-specific variation: stomatal conductance (crops > hardwoods > conifers), high conductance allows more ozone to enter the leaf

• Conifers sensitive to ozone: ponderosa pine, jeffery pine, and white fir (Abies concolor)

• Intra-specific variation: black cherry and loblolly pine genotypes support a positive correlation between genetic differences in stomatal conductance and foliar ozone sensitivity (however, higher foliar damage was not always associated with greater growth reduction)

• Ontogenetic variation: sensitivity to ozone differed between young and mature trees in many cases (highest conductance associated with the most sensitivity to ozone)

• Intra-tree variation: position within crown, sun versus shade leaves etc.

Susceptibility to ozone (continued)

Spatial distribution of [O3]

• Symptoms of damage by ozone influenced by both endogenous and exogenous factors, a clearly defined cause and effect relationship has not been established;

• Ozone sensitivity affected by: tree species, developmental stage, microclimate, and ability to compensate for ozone injury through leaf production, alteration in carbon partitioning and allocation;

• Tremendous variability exists within natural systems;

• Scaling continues to necessitate future research

(Chappelka and Samuelson 1997)

Ambient ozone effects on forest trees of the eastern US (summary)

Ozone on forests in Europe• Critical levels of ozone (AOT40, accumulated

exposure of O3 over a threshold of 40 nl l-1)• Level I-define where adverse effects of O3

might occur• Level II-estimate impacts of O3 in the field• Today, only Level I approach has been adopted• It must be recognized that critical levels for

forest trees are not definitive or absolute based on the best available knowledge (Skarby et al. 1997).

• Insufficient evidence to support annual exceeding AOT40 will have negative effects on forest tree growth, but good evidence to support the risk of reduction in yield is high;

• Changes in photosynthetic rates, carbohydrate production, C allocation and translocation etc. are key factors influencing tree growth, and ultimately survival;

• Interactions between O3 and climatic stress, particularly drought and frost hardiness, are likely to result in potentially detrimental effects.

Ozone on forests in Europe (continued)

(Skarby et al. 1997)

Ozone destruction/depletion

• Ozone is destroyed by reactions with chlorine, bromine, nitrogen, hydrogen, and oxygen gases through catalytic processes

• Antarctic ozone hole (first reported in 1985)• Man-made materials such as CFCs or

chlorofluorocarbons are now known to have a very dramatic influence on reducing ozone level

What is it?The Antarctic ozone hole is an area of the Antarctic stratosphere in which the recent (since about 1975) ozone levels have dropped to as low as 33% of their pre-1975 values. The ozone hole occurs during the Antarctic spring, from September to early December, as strong westerly wind start to circulate around the continent and create an atmospheric container. In this container over 50% of the lower stratospheric ozone is destroyed.

Chemical equation

CFCl3 + UV Light ==> CFCl2 + ClCl + O3 ==> ClO + O2ClO + O ==> Cl + O2

The free chlorine atom is then free to attack another ozone molecule

Cl + O3 ==> ClO + O2ClO + O ==> Cl + O2

and again ...Cl + O3 ==> ClO + O2ClO + O ==> Cl + O2

and again... for thousands of times.

Spectrum region

Wavelength % total energy

Comments

Infrared > 700 nm 49.4 Heat

Visible 400-700 nm 42.3 Photosynthesis

UVA 400-320 nm 6.3 Bronzing of skin and suntan

UVB 320-290 nm 1.5 Sunburn to skin cancer

High absorption by plants

UVC < 290 nm 0.5 Near complete atmospheric attenuation

(Source: http://www.epa.gov/uvnet)

Ozone hole: natural or human-made chemicals caused?

• Controversy

• “Scientific knowledge is a body of statements of varying degrees of certainty-some most unsure, some nearly sure, but none absolutely certain”

-Nobel Prize physicist Richard Feynman (1918-88)

UV-B + CO2 on photosynthesis and growth

• CO2 enrichment may provide protection to the photosynthetic apparatus or compensate for UV-B damage

• UV-B may limit the ability of plants to exploit elevated CO2 in some species

• Species specific biomass allocation altered• Community- seedling establishment and

competition, phenology and reproductive output- to ecosystem process (e.g. decomposition and nutrient cycling)

(Source: Sullivan 1997. Plant Ecology 128: 194-206)

Interactive effects of N deposition, tropospheric O3, elevated CO2, and land use history on the

carbon dynamics of northern hardwood forests (Ollinger et al. 2002, Global Change Biology, 8: 545-562)

• The combined effects of all physical and chemical factors produced growth estimates were similar to those obtained in the absence of any form of disturbance

• Intact forests may show relatively little evidence of altered growth since preindustrial times despite substantial changes in their physical and chemical environment

Small, fragmented, and isolated populations

Reduced adaptability, survival, and reproduction

Inbreeding and loss of genetic diversity

Reduced population size

Extinction Vortex

Habitat loss Pollution Over-exploitation Exotic species

Demographic stochasticity

Environmental change

Catastrophic events

(Frankham et al. 2002)

State of science and gaps in our knowledge in relation to air pollution

• Mechanisms of action and indicator development -State of science: ozone injury from molecular (salicylic

and jacmonic acid regulated defense genes) and gene marker, gas exchange and water relations under CO2 and O3, N and P dynamics in determining plant response to elevated, modeling O3 uptake

-Gaps: only few model plant species (poplar, birch, Arabidopsis); scaling from molecular to ecosystem levels with specific reference to root physiology, plant competition, and progeny fitness; working tools (OTC, FACE, field plots); combination of ecophysiology, molecular biology, and modeling---multidisciplinary approach

State of science and gaps in our knowledge in relation to air pollution (continued)

• Atmospheric deposition, soils, and biogeochemistry

-State of science: importance of dry deposition of gases and particulates; nitrogen deposition to soil nutrition and affect forest ecosystems; competition from weeds to ponderosa pine seedlings in response to O3; decomposition; modeling; CO2 + O3 in FACE study

-Gaps: biogeochemical cycle, and soil system in response to multiple stresses; forest and water; linking atmospheric, plants, and soil components; large-scale research approach and use of passive samples

Sources

Physical and chemical transformation to secondary pollutants

Emission of primary air pollutants (SO2, NOx, NH3, CO, (CH)n, PM…)

Meteorology (dispersion and transport)

LegislationControl measures

Wet and dry deposition (acid rain)

Photochemical smog (ozone)

Control strategy options

transport modelsAmbient airMonitoring

Impacts

Air pollution system (Finlayson-Pitts and Pitts 1986)

Control of air pollution• Particulates- fugitive source (waste pile)-

protecting open areas by cover, dust control by water, reducing the effect of wind by plantation

• Automobile pollution-exhaust restriction and emission control, reduce number of cars on the roads, development of cleaner fuels

• Acid rain-long-term solution is to reduce the emission of SO2 and NOx, increasing energy efficiency, conservation measures, and alternative nonpolluting energy sources

Government Regulation

• Emission standards-”reasonably available control technology” for “best practical means” approach

• Air quality standards versus critical levels (the critical level is based solely on the best available scientific knowledge and understanding, “threshold”, critical level not for compliance purpose)

• Emission taxes (e.g. US EPA to implement the goals of the Montreal Protocol, on CFCs use)

• Cost-benefit analysis approach

Summary (1)• Human activity contributes majority of the

pollutants of sulfur and nitrogen oxides in the atmosphere-primary pollutants

• The secondary pollutants-acid rain/deposition and ozone caused significant damages to both human and natural systems

• The effects of acid rain/deposition depends on the elevation, land use, regions, and soil acid neutralizing capacity

• Ozone remains as one of the big concerns in the field of air pollution effects on forest ecosystems; mechanisms of impacts: from molecular to ecophysiological process

Summary (2)• Numerous reports suggested forests affected by air

pollution, the extent remains uncertain• Routine monitoring systems provide many data, yet

often they do not fit statistical requirements for detecting status and trends of forest health

• There is a clear need for a new examination of monitoring concepts, designs, and choice of ecological indicators

• Much work remains to be done, particularly in the areas of scaling up to landscape under multiple stressors

Email: [email protected]: +928-523-8978

Questions??