ENSC 412612 Week 2 Air Quality, Standards, Sources

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ENSC 412/612 Week 2Air Quality, Standards,
Sources

• READINGS FOR THIS WEEK
• Text CHAPTERS 4,6,22

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Air Quality

• Ambient air quality -- refers to concentrations
  of pollutants in OUTDOOR AIR (differentiate from
  INDOOR AIR POLLUTION)
• Pollutant concentrations are highly variable in
  space and time WHY?

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• variations in emission rate
• variations in transport and diffusion mechanisms
  in atmosphere
• scavenging and conversion in the atmosphere --
  pollutant half-life
• Ambient concentrations are typically cyclic
  What are the cycles?

4

• annual variation in PM10 shows influence of dust
  episodes in late winter / early spring as roads
  dry out

• PM2.5 levels are highest in fall and winter due
  to combustion combined with stagnation events

NOTE figures from Suzuki and Wallis, 2003.
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• PM10 diurnal variation responds to traffic
  (dust)

• PM2.5 can see the influence of fumigation
  events (late morning) on the 95th and 98th
  percentiles

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• hebdomodal variability shows higher levels of
  PM10 during the week reflecting traffic and work
  patterns that generate dust (episodes caused by
  dust sources)

• PM2.5 have somewhat lower median and mean values
  during weekends, but 95 and 98th percentile
  values show no weekly trend (episodes caused by
  combustion sources which operate 24/7)

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Cycles of ambient pollutant levels

• diurnal (source strength, transport and
  diffusion)
• weekly (weekend vs weekday emission differences)
• seasonal (source strength, transport and
  diffusion)

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Diurnal cycle
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Impact of averaging time
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Trends

• Changes from year to year are trends.

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Trends in PM10/PM2.5
1995
1997
1999
2003
2005
2007
2001
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National Trends in O3 and PM2.5

• Ozone
• PM2.5

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Primary and secondary pollutants

• Substances emitted directly to the atmosphere are
  PRIMARY POLLUTANTS.
• Chemical reactions among primary pollutants and
  with the atmosphere form SECONDARY POLLUTANTS.

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Responses to Air Pollution
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Sources - Natural

• volcanos - particulates, SO2, H2S, methane, etc.
  can affect globe
• forest fires - smoke, unburned HC, CO, CO2, NOx,
  ash
• dust storm
• oceans - salt aerosols
• plants / trees - major source of HC - blue
  haze'' over forests is a reaction of volatile
  organics
• pollen, bacteria, rust, etc.

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Sources - Anthropogenic

• Industrial stationary, consistent emissions,
  mostly from manufacturing products from raw
  materials
• iron from ore
• lumber and paper from trees
• gas from crude oil
• stone from quarries
• Also when products are made into new products
• cars from steel
• furniture from lumber
• paint from solids and solvents
• asphalt from rock and oil

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Anthropogenic Sources contd

• 2. Utilities Power generation (e.g. coal
  burning to generate electricity) sewage
  treatment (sludge burning) burning dump (not
  common anymore)
• 3. Personal sources
• automobiles
• home furnaces
• home fireplaces
• BBQ
• backyard burning of garden wastes

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Personal Sources

• In our society, total personal sources are
  greater than both industrial and utility sources
  combined. Personal sources are probably the most
  difficult to control since they require the
  cooperation (subjugation?) of a large number of
  individuals and usually involve extra expense
  and/or lifestyle changes, eg
• regulations
• lifestyle changes
• change fuel to one with less emissions
• improve efficiency
• change form of pollution (eg. haul leaves to the
  dump instead of burning them)

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Combustion

• One of the most widely used but least understood
  chemical reactions (it is a free radical chain
  reaction).
• the rapid union of a substance with oxygen
  accompanied by the emission of light and heat.
• used mostly for heat by changing the potential
  chemical energy of the fuel to thermal energy.
• also used as a means of destruction of unwanted
  materials. The volume of solids is reduced,
  combustible gases with odours etc., are converted
  to less objectionable gases.
• C O2 ? CO2  
• 2H2 O2 ? 2H2O 

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• Products of burning are carbon dioxide and water,
  which are odourless and invisible.
• Problems occur because the process also produces
  other products, many of which are pollutants
  carbon monoxide, carbon dioxide, oxides of
  sulfur, oxides of nitrogen, smoke, fly ash,
  metals, metal oxides, metal salts, aldehydes,
  ketones, acids, polynuclear hydrocarbons, etc.
• It was only recently that these by products were
  considered important due to their negative
  impacts.

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• Efficient combustion requires 3T's
• time (to occur fully),
• temperature (to initiate and maintain), and
• turbulence (to ensure that the reacting fuel and
  oxygen molecules in the combustion process are in
  intimate contact).
• The physical state of the fuel determines how
  combustion will occur.
• A fuel can be a volatile material - burns with a
  flame fixed carbon - no visible flame or both.

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• Gaseous fuels burn easily
• liquid fuels must first be vapourized either by
  supplying heat, or by atomizing the fuel and then
  spraying it into a heated combustion chamber to
  accomplish gasification.
• solid fuels such as coal or wood require several
  steps to burn (drying, distillation, carbon
  burning, ash discharge)

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• Typical emissions from combustion

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Stationary Sources

• See text Chapter 6 for a discussion of various
  stationary sources. (Chemical, Resins and
  Plastics, Varnish and Paints, Acid manufacture,
  Soaps and detergents, Phosphate fertilizers,
  Inorganic chemicals, Petroleum and coal, Primary
  metals, Stone and clay products, Forest products,
  Noxious trades (smell, eg animal processing).

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Mobile Sources

• Vehicles powered by different types of engines,
  using different fuels.
• Largest source in western society.

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Emission Inventories

• A list of the amount of pollutants from all
  sources entering the air of a given area over a
  given period of time.
• This information is very useful to control
  agencies, as well as land use planners
• what are the sources and what are their relative
  sizes?
• Can be used
• as input into dispersion models to predict
  ambient pollution levels,
• design a sampling network (both location and type
  of sampling), and
• assess impact of pollutants on various areas.

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EI- continued

• Estimation methods are error prone however.
  Creating an inventory involves the following
  steps
• list types of sources in an area
• determine which pollutants are emitted from each
• find emission factors for each pollutant (amount
  of pollutant produced for each unit of input into
  the process, eg fuel)
• determine number and size of specific sources in
  area
• multiply numbers and sum to find total emissions
• There is a lot of variation in emission factors.
• Emission factors for a number of sources can be
  found at the US EPA's web site (http//www.epa.gov
  ).

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Air Quality Standards

• Objective of air quality management is to control
  emissions so that ambient concentrations do not
  exceed standards.
• Toward this the federal NAAQO's were established
  (National Ambient Air Quality Objectives).
• There are three criteria levels
• level A - maximum desirable'' long-term goal
  and is also the basis for an anti-degradation
  policy in unpolluted areas
• level B - maximum acceptable'' provide
  adequate protection against effects of pollutants
  on human health and discomfort, soil, water,
  vegetation, animals, and visibility.
• level C - maximum tolerable'' concentration
  beyond which action is required quickly to
  protect health of general population.

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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), and BCMoE have a PM2.5
objective of 25 µg / m3 for a 24 hour average, 8
µg / m3 for an annual average with 6 µg / m3 as
the goal.
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• Levels are defined based on laboratory and
  epidemiological experiments and studies.

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Readings for next week

• Text chapters 28, 29, 30, 31
• Millar (2007) paper