Air Quality Considerations

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Air Quality Considerations

• Sources ? Atmosphere ? Receptors

All must be considered! Most AQ issues are
complex and solutions that work can be
challenging What we care about are impacts on
Receptors (i.e. people)
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Sources

• No source no pollution!
• Amount, configuration, characteristics all
  important
• Total discharge of a particular source may not be
  as important as other factors (e.g. elevation of
  emission, distance from population)

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Atmosphere

• Acts to dilute, disperse, transform, remove
  pollutants, as well as transporting them between
  source and receptor
• Most AQ episodes are due to atmospheric
  conditions, not emission changes
• Inversions and light winds associated with High
  Pressure systems cause episodes in PG

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Receptors

• Where pollution is received and has impact (where
  people live and work)
• Different pollutants will have different impacts
  (e.g. PM vs TRS)
• Health issues, environmental degradation,
  visibility, nuisance / odor, etc.

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Air pollution in the boundary layer

• There are several important emission properties
  amount, physical and chemical nature of
  pollutants, shape of emission area, duration of
  releases, effective height at which injection of
  pollutants occurs.
• After release, the dispersion of pollutants is
  controlled by turbulence or atmospheric motion.
• Stability, wind speed, roughness are some of the
  key atmospheric parameters, whereas wind
  direction variability determines the extent of
  wind spreading.

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• While in the atmosphere, pollutants may undergo
  physical and chemical transformations that are
  related to meteorological characteristics water
  vapour/cloud, temperature, incoming solar
  radiation, etc.
• The removal of pollutants by precipitation
  (scavenging), by settling/absorption and
  impaction is related to the state of the
  atmosphere.
• In general the atmosphere is highly dispersive.

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Oke (1987)
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Sulfur Components

• Mostly SO2 (sulfur dioxide), H2S (hydrogen
  sulphide), but also sulfurous (H2S3) and sulfuric
  (H2SO4) acid.
• SO2 is a waste product from fuel burning.

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Oxides of Carbon (COx)

• Carbon monoxide (CO) arises from incomplete
  combustion.
• Carbon dioxide (CO2) is a product from fossil
  fuel burning.

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Hydrocarbons

• The most natural hydrocarbon is from
  decomposition of vegetation.
• It is also produced by combustion of fossil fuels
  and evaporation of gasoline.

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Oxides of Nitrogen (NOx)

• Nitrogen oxides are naturally produced during
  decomposition.
• Anthropogenic releases accompany combustion of
  fuel -- nitric oxide (NO) which oxidizes to give
  nitrogen dioxide (NO2).
• This is a brown irritant from cars, coal,
  fertilizers, etc.

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Particulates

• Approximately 90 of particulates are natural,
  and the other 10 have an anthropogenic source.
• Because of their weight, particulates tend to
  settle out near their source.
• Particles lt 10 µm can remain suspended longer,
  and those lt 1 µm may be in suspension for several
  days (such as during haze).

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Other Pollutants

• In addition, there are a number of minor
  pollutants emitted in small quantities -- because
  of toxicity these may be significant (e.g.,
  hydrogen fluoride, fertilizers, toluene (paint
  and solvents), radioactive substances, ammonia
  (chemical fertilizer).
• There are also secondary pollutants that are
  created by chemical reactions in the atmosphere
  (between pollutants or between pollutants and
  natural constituents).
• For instance ozone (O3), peroxyacetyl nitrate
  (PAN) and aldehydes arise from photochemical
  reactions.

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• Cars are the largest source of pollutants in
  North America so that the pollutant mix is
  dominated by CO, NO, NO2, HC and particulates.
• Add sunlight to the mix and the result is
  photochemical smog and secondary pollutants.
• Also require information on the source
  configuration ? shape, duration, height (point
  source, line source, area source).

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Oke (1987)
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Atmospheric Controls

• Largely controls vertical movements of
  pollutants.
• Unstable ? large eddies ? enhanced vertical
  diffusion.
• Stable ? decreased turbulence and diffusion.
• Presence of inversions is very important for
  vertical diffusion.
• There are several types of inversions 1)
  surface-based, nocturnal 2) subsidence warming
  and 3) advective (such as associated with warm
  fronts, advecting warm air over a cold surface).
• The latter are not as important for air pollution
  as the air is usually in movement.

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Oke (1987)
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Oke (1987)
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Effect of wind

• Wind diffuses pollutants by stretching them along
  the wind direction.
• Wind speed also enhances turbulence, and thus
  vertical and horizontal diffusion.
• Variations in wind direction are also important
  as they lead to sinuous plumes

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Oke (1987)
21
Oke (1987)
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• The greatest potential for pollution is in low
  wind situations because horizontal transport and
  turbulent diffusion are both curtailed.
• Local circulations (land/sea breezes etc.) are
  not good pollution ventilators because they are
  associated with low wind speeds, they are closed
  systems, and there usually is a diurnal reversal
  ? pollution comes back.

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• Depending on local meteorology, pollution may
  recirculate, thus increasing concentration over a
  period of days.
• Topography and/or climate conspires to limit
  ventilation (e.g., Vancouver, Prince George, Los
  Angeles, or Mexico City).

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Pollutant removal

• Gravitational settling removes particulates gt 1
  µm, with those gt 10 µm settling quickly.
• Gaseous pollutants can be absorbed onto particles
  and removed with them.
• Deposition (surface absorption) is a turbulent
  transfer (flux) of pollution to the ground,
  analogous to heat, water vapour, etc., fluxes.

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• Fp - KP ??/?z
• Where Fp is the pollutant flux that depends on
  the eddy diffusivity of the matter (Kp) and on
  the pollutant (?) concentration gradient.
• Another mechanism for pollutant removal is
  through precipitation that scavenges pollutants
  from the air.
• This effectively cleanses the air of gases and
  small particulates, some of which may become
  condensation nuclei for raindrops or snowflakes.
  Falling precipitation can also collect material
  (washout).

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Processes of pollutant transformations

• This is a complex and not well understood topic
  (atmospheric chemistry).
• Two transformations of importance are
• 1) transformations of the oxides of sulfur ?
  sulfurous (London-type smog).
• 2) transformation of the oxides of nitrogen and
  hydrocarbons ? photochemicals (L.A. - type
  smogs).

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• SO2 is a primary pollutant from the combustion of
  fuels ? oxidizes to form sulfur trioxide (SO3)
  that reacts with water vapour (H2O) in the
  presence of catalysts to form sulfuric acid mist
  (H2SO4).
• H2SO4 may combine with other things to form
  sulfate particles which settle out.
• An exceptional example occurred in London, in
  1952, where over a period of 4-5 days about 4000
  people were killed.

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• From action of solar radiation on nitrogen oxides
  in the presence of secondary pollutants (ozone,
  oxygen, NO2, peroxyacetyl nitrates PAN)
• Odour, brownish haze (NO2 and particles), and
  throat irritations (O3), aldehydes, PAN), plant
  damage (O3, NOx, PAN, ethylene)
• Fullest expression is in low latitude (lots of
  solar radiation) in urban environments (lots of
  cars).

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Air Quality Issues in Prince George
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Air Quality Management

• Goal is to lower ambient levels of particular
  pollutants to a level sufficient to protect
  health, environment and quality of life
• Decision makers have to weigh information from
  various sources and experts, as well as
  potentially competing interests (e.g. health,
  environment, economy) on behalf of the public

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BC Ambient Air Quality Objectives
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1.
2.
3.
4. Also for PM2.5 Canada Wide Standard in
2010 will be 98th percentile of 30 µg / m3
averaged over 3 years (can exceed 30 only
2 of the time 7 days / year)
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PG Topography

• PG in a bowl
• bowl restricts free mixing of air and dilution
  of pollution
• especially under inversion conditions and light
  winds

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• Annual wind roses

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source 2007 and 2003 Annual Air Quality Report
for Prince George, BCMOE

• TRS the smell
• Dominant source
• is pulp mills

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source 2007 Annual Air Quality Report for
Prince George, BCMOE
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Particulate Matter What is it?

• An airborne atmospheric particle
• PM10 - a particle of 10 microns, about 1/5th the
  width of a human hair.
• PM2.5 - a particle of 2.5 microns, about 1/20th
  the width of a human hair
• BC Ministry of Health has called PM single
  greatest air pollution problem in BC
• PM10 travels into the lungs and cause a variety
  of respiratory problems
• PM2.5- penetrates the respiratory system deeper
  and is therefore more of a problem than the sizes
  gt 2.5 microns

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• PM size distribution is bi-modal.
• coarse mode generally results from mechanical
  breakdown of larger particles
• fine mode generally results from combustion
  processes and secondary particulates

Source Seinfeld (1986)

• PM2.5 is about 15 dust and the rest from
  combustion it can be used as a measure of
  ambient conditions due to combustion sources
• The coarse fraction (PM10 PM2.5) comprises 85
  of the dust

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Typical PM2.5 Components

• Geological Material suspended dust consists
  mainly of oxides of Al, Si, Ca, Ti, Fe, and other
  metal oxides.
• NaCl salt is found in PM near sea coasts, and
  after de-icing materials are applied.
• Sulfate secondary particulate resulting from
  conversion of SO2 gas to sulfate-containing
  particles.
• Nitrate secondary particulate resulting from a
  reversible gas/particle equilibrium between NH3,
  HNO3, and particulate ammonium nitrate.

• Ammonium ammonium bisulfate, sulfate, and
  nitrate most common.
• Water (liquid) soluble nitrates, sulfates,
  ammonium, sodium, other inorganic ions, and some
  organic material absorb water vapor from the
  atmosphere.
• Organic Carbon (OC) consists of hundreds of
  separate compounds containing mainly carbon,
  hydrogen and oxygen.
• Elemental Carbon (EC) composed of carbon
  without much hydrocarbon or oxygen. EC is black,
  often called soot.

Chow and Watson, 1997
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PM Bottom Line

• Smaller particles (PM2.5) are worse than larger
  particles (coarse part of PM10)
• Particles from combustion more harmful than
  particles from dust
• Many sources of PM are hard to quantify

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Sources of PM

• Industrial processes
• Dust
• Locomotive engines
• Heating
• On-road mobile
• Burning
• Chemical transformations of gases (e.g. SO2) to
  sulfate (secondary particulates)
• Many others
• Diversity of Sources Makes PM difficult to manage!

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Draft Emission Inventory (with rail emissions
revised, but further changes have also been
identified)
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PM10 2007 (continuous)
BC Rail
Plaza
Gladstone
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• Plaza PM10

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PM2.5 2007 (continuous)
Plaza
Gladstone
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• Plaza PM2.5

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PM10 comparison with other BC communities
Risk factor is a relative health index
normalized to 2000 average values based on
increments gt 25 ug/m3
source 2004 Annual Air Quality Report for
Prince George, BCMOE