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)
Major air pollutants
•
•
•
•
•
•
•
•
•
•
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
• 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 industryproduce 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
Atmospheric trace gases that are radiatively active and
of significance to global change (EarthQuest 1990)
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
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 pollutantsnamely peroxyacetyl nitrates
(PAN) and ground-level
(tropospheric) ozone.
Ozone
[O3]
O2
UV light
Sulfur dioxide
[SO2]
[O]
NO2
Peroxyacetyl
nitrate
(PAN)
CH3-CO-ONO2
O
Air:
Nitrogen 78%
CO2 and CO
NO
UV light
Oxygen 21%
CO2 0.03%
Fuel:
Hydrocarbons
Sulfur contaminant 1-6%
Additives (tetraethyllead)
Combustion,
heat, and
pressure
Unburned
hydrocarbons
Lead
(particulate)
Plant-pathogenic air pollution resulting from the
combustion of fossil fuels (Manion 1991)
Solar radiation
Burning coal or oil in
an urban area
NOx
Organic
+ Compounds
Hydrocarbons
With presence of an inversion
layer, trapping pollutants
Concentrated
photochemical
smog (brown air)
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
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) Precursor of acid rain/deposition
4) Directly results in injury to death of plants
and animals, severe damage to respiratory
system
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/s
4/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
Fossil fuel combustion
Biomass burning
Lightning
Microbial activity in soils
Oxidation of ammonia
Biological processes in the ocean
Input from the stratosphere
Total
Nitrogen
(1012 g/year)
21 (14-28)
12 (4-24)
8 (2-20)
8 (4-16)
1-10
>1
About 0.5
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
Acid deposition variations
(cont’d)
• 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!
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
Pollution-related forest declines
of the past 50 years (cont’d)
• 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)
• 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 Acidification in soils in many
developed countries but increase in parts of the world and difficult
developing countries, stable
to mitigate
globally
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
Ozone Precursors
(Sources: http://www.theozonehole.com/ozone.htm)
Patterns of ozone exposure
• Seasonal: summer highest, related to
temperature and UV radiation
• Diurnal: 1) far from urban areasconcentrations 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 areasconcentration rise beginning at sunrise, peak
by early afternoon and then decrease
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 compoundsdefense 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 stresspredispose 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 lengthbased 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)
Assessing O3 injury
•
•
•
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)
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)
Susceptibility to ozone
(continued)
• 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.
Spatial distribution of [O3]
Ambient ozone effects on forest trees
of the eastern US (summary)
• 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)
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).
Ozone on forests in Europe
(continued)
• 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.
(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 + Cl
Cl + O3 ==> ClO + O2
ClO + O ==> Cl + O2
The free chlorine atom is then free to attack
another ozone molecule
Cl + O3 ==> ClO + O2
ClO + O ==> Cl + O2
and again ...
Cl + O3 ==> ClO + O2
ClO + O ==> Cl + O2
and again... for thousands of times.
Spectrum Wavelength
region
Infrared > 700 nm
% total
energy
49.4
Comments
Visible
400-700 nm
42.3
Photosynthesis
UVA
400-320 nm
6.3
UVB
320-290 nm
1.5
UVC
< 290 nm
0.5
Bronzing of skin and
suntan
Sunburn to skin cancer
High absorption by
plants
Near complete
atmospheric
attenuation
Heat
(Source: http://www.epa.gov/uvnet)
Ozone hole: natural or humanmade 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
• Communityseedling establishment and
competition, phenology and reproductive
outputto 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
Habitat loss
Pollution
Over-exploitation
Exotic species
Small, fragmented, and
isolated populations
Demographic
stochasticity
Reduced
population size
Extinction
Vortex
Inbreeding and loss
of genetic diversity
Environmental
change
Catastrophic
events
Reduced adaptability,
survival, and reproduction
(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
Control
measures
Legislation
Emission of primary air
pollutants (SO2, NOx, NH3, CO,
(CH)n, PM…)
Meteorology (dispersion
and transport)
Monitoring
Wet and dry
deposition
(acid rain)
Physical and chemical
transformation to
secondary pollutants
Ambient air
Control strategy
options
transport models
Photochemical
smog (ozone)
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
Questions??
Email: Zhong.Chen@nau.edu
Phone: +928-523-8978