Climate change and pollution

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Climate change and pollution

• Eleanor J Highwood
• Department of Meteorology, University of Reading
• MSc Intelligent Buildings April 2002

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Outline climate change

• What is climate?
• Has climate changed in the recent past?
• If so has any change been unusual?
• What might have caused climate to change?
• Can we model climate change?
• What might happen in the future?
• What is there left to do?

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What is climate?

• Climate is what we expect, weather is what we
  actually get
• A full description of climate includes
• global means, geographical, seasonal and
  day-to-day variations of
• temperature, precipitation, radiation, clouds,
  snow cover etc.

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Has climate changed in the recent past?

• Temperature changes
• Sea level rise
• Precipitation changes
• Mountain glaciers
• Snow cover

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Temperature changes 1

• Global mean T of air at Earths surface has ? by
  0.6 /- 0.2 C over the 20th century.

IPCC 2001
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Temperature changes 2

• Regional changes can be much larger than global
  means some places have also cooled global
  warming is a misnomer.
• Size of warming depends on time period considered
  and time of year considered.

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Variation of warming with time period IPCC 2001
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Seasonal variation in warming IPCC 2001
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Temperature changes 3

• Over the period 1950 to 1993, diurnal temperature
  range has reduced because the nights have warmed
  more than the days.

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Sea level changes

• Observed rise of 0.1 - 0.2m during 20th century.
  Rises are of order 2mm/year
• Mostly due to thermal expansion of oceans

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Precipitation changes

• ?? over land in tropics and mid-latitudes and ?
  in the subtropics.
• NH mid-latitudes have seen an increase of 2-4 in
  frequency of heavy precipitation events

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Mountain glaciers

• Shrinkage of many glaciers since 1890. If it
  reaches the oceans this contributes to sea-level
  rise.

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Snow cover

• 10 reduction in NH snow cover between 1960s and
  present day

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Sea ice

• NH sea ice extent has decreased by 10-15 since
  1950s

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Have changes been unusual?

• Proxy records
• tree rings (past 100 years)
• shallow ice cores
• corals
• deep sea sediments (past 10, 000 years)
• Natural variability changes resulting from
  interactions between components of climate system

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Changes over past 1000 years (from Mann et al
1999
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Natural variability1
There have been large changes in temperature in
the past
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Natural variability2

• Even a climate with no forcing has a lot of
  variability (IPCC 2001)

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What might have caused these changes?

• The balance of evidence suggests that there is a
  discernible human influence on global climate
  (IPCC, 1995)
• There is new and stronger evidence that most of
  the warming over the past 50 years is
  attributable to human activities (IPCC 2001)

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Fundamental processes

• Many interacting components

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Energy balance
Solar energy absorbed by the Earth-atmosphere
system
Energy radiated from Earth- Atmosphere system to
space

S0 (1- ?p) ?re2 4 ?re2 ? Te4
30 of incoming solar radiation reflected to
space by clouds, surface, molecules and particles
in the atmosphere (albedo).
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Radiation and climate
IPCC 2001
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The natural greenhouse effect
??Ta4
??Ts4
??Ta4
Atmosphere absorbs radiation from ground and
re-emits less radiation since it is colder
(?0.77)
Earth radiates to space
Atmosphere traps radiation and warms surface so
that life can exist.
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Radiative forcing, ?F

• Radiative forcing measures the change to the
  energy budget of the atmosphere.
• Positive ? surface T ?
• Negative ? surface T ?
• Easier to calculate than change in temperature,
  but related to temperature change by ?T ??F
  where ? is the climate sensitivity.

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Radiative forcing due to ? in solar output

• ASR OLR

System in balance
ASR gt OLR
OLR must increase to balance ASR, so system must
warm up. ?F ve
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Radiative forcing due to ? in carbon dioxide

• ASR OLR

System in balance
OLR lt ASR
OLR must increase again to balance ASR, so
system must warm up. ?F ve
CO2 raises ?? so more radiation comes from cold
atmosphere so OLR increases
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Possible causes of climate change
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Natural climate change

• Solar variability
• Volcanic eruptions

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Solar variability 1

• Changes in the Suns strength
• 11 year cycle with sunspots
• small changes

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Solar variability 2

• Changes in Sun-Earth geometry
• Sun-Earth distance, tilt of Earth and ellipse of
  orbit
• act over very long timescales, many thousands of
  years
• possibly play a role in inducing ice ages but not
  important on past 250 years time scale
• at current time provides a cooling influence on
  climate

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Volcanoes
Large eruptions like Pinatubo (1991) put clouds
of sulphur dioxide gas into stratosphere, above
the weather. ?? cloud of sulphuric acid droplets
scatter and absorb solar radiation ? cooling of
surface and warming of stratosphere
But, aerosols only last a few years, so generally
climate impact only lasts a few years (apart from
cumulative effect? )
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Observed effect on T
IPCC 2001
El Chichon
Pinatubo
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Anthropogenic causes

• Greenhouse gases
• Ozone changes (stratospheric and tropospheric)
• Tropospheric aerosols
• Surface albedo changes
• Heat pollution

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Greenhouse gases 1

• Water vapour is most important natural greenhouse
  gas, but we dont usually change it directly
• Strength of a greenhouse gas depends on
• strength of absorption of infra-red radiation
• overlap of absorption with other gases
• lifetime in the atmosphere
• amount added over given period of time

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Greenhouse gases 2

• CO2 (carbon dioxide)
• CH4 (methane)
• N2O (nitrous oxide)
• CFCs/HCFCs/HFCs (chlorofluorocarbons/hydrochlorofl
  uorocarbons/hydrofluorocarbons)

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Strengths of greenhouse gases
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CO2 1

• Risen by 31 since 1750, roughly in line with
  emissions from fossil fuel burning

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CO2 2

• Rate of recent increase has been unprecedented
• Also increased by deforestation in the tropics
  and biomass burning
• Lifetime of 200 years and is slow to respond to
  changes in emissions

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Carbon cycle
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CH4 1

• Increased by 50 since 1750 and continues to
  increase.

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CH4

• Current concentrations have not been exceeded in
  420 thousand years
• From rice-growing, domestic cattle, waste
  disposal and fossil fuel burning
• 12 year lifetime (a quick-fix for global
  warming)

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N2O

• Increased by 17
• Unprecedented in past 1000 years
• Half of current emissions are anthropogenic
  (fertilisers etc)

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CFCs

• CFCs contain chlorine which damages the ozone
  layer in the stratosphere. They last 50 years or
  more and so built up in the atmosphere during
  1970s/80s. Banned under Montreal
  Protocol?Replaced temporarily by HCFCs which
  still contain chlorine but break down in
  atmosphere much more quickly

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HFCs

• No chlorine (therefore dont affect ozone layer)

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HFCs

• No chlorine (therefore dont affect ozone layer)
• BUT
• they are powerful greenhouse gases and very
  long-lived
• Entirely anthropogenic in origin (and used in a
  variety of odd ways!)
• Rising quickly in the atmosphere

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Emission of CFCs etc
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CF4
SF6
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Ozone

• Spatially non-uniform
• Radiative forcing depends critically on level at
  which ozone changes
• troposphere ozone has increased and produces a
  positive radiative forcing
• stratosphere ozone has decreased implying less
  absorption and re-emission of IR radiation
  producing a negative forcing (also small ve
  forcing due to increased solar radiation reaching
  the surface)

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Tropospheric ozone changes
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Tropospheric aerosols

• Tiny particles (or droplets)
• Many different types from both natural and
  anthropogenic sources
• dust (from land-use change)
• sulphates (fossil fuel burning)
• soot (fossil fuel and biomass burning)
• organic droplets (fossil fuel and biomass burning)

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Aerosols Direct solar effect

• Aerosols scatter and absorb solar radiation

No aerosol
Scattering aerosol
Absorbing aerosol
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Aerosols Direct terrestrial effect

• Large aerosols (e.g. dust or sulphuric acid in
  the stratosphere) behave like greenhouse gases.

Aerosol absorbs radiation from ground and
re-emits a smaller amount up and down
No aerosol ground emits to space
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Aerosols Indirect effects

• Some aerosols can alter the properties of clouds,
  changing their reflectivity or lifetime

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Aerosol forcing

• Magnitude and sign of forcing depends on
  distribution and mixing
• Very spatially non-uniform distributions

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Aerosol forcing

• Cannot be used to cancel out greenhouse gas
  forcing (patterns are completely different)
• Response may also be different
• Indirect effect is very uncertain but potentially
  large

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CO2 vs aerosol forcing
CO2
Sulphates
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Land albedo changes

• Land use changes alter the albedo and the amount
  of solar radiation reflected back to space.

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Heat pollution

• Urban and industrial regions output large amounts
  of local heat.
• Important regionally and may modify the
  circulation

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Radiative forcing since 1750

• GHG 2.43 Wm-2 (60 CO2, 20 CH4)
• Tropospheric ozone 0.35 Wm-2
• Stratospheric ozone -0.15 Wm-2
• Tropospheric aerosols (direct)
• sulphates (-0.4 Wm-2), biomass (-0.2 Wm-2),
  organics (-0.1 Wm-2), black carbon (0.2 Wm-2),
  dust ?
• Indirect effect -0 to -2 Wm-2
• Solar /- 0.2 Wm-2

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Can we model climate change?

• At the simplest level we can relate
• ?T??F
• But what is ?? Represents feedbacks between
  climate components.
• Many feedbacks, three very important ones.

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Water vapour - temperature feedback
? T (e.g. due to CO2)
More evaporation at the surface
Water vapour is a greenhouse gas, therefore
ve feedback
More water vapour in the atmosphere
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Snow/ice - temperature feedback
? T (e.g. due to CO2)
Less snow and ice
More solar energy is absorbed at the surface,
therefore
ve feedback
Planetary albdeo increases
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Cloud feedback

• Clouds can reflect solar radiation (low thick
  clouds) and act as greenhouse gases (high thin
  clouds)
• Uncertain as to how clouds changes in a changing
  climate or how these changes would feedback to
  climate
• positive or negative feedback?

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Other feedbacks

• biosphere

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Climate modelling

• We use climate models to
• model present day climate and understand physical
  processes
• model past climate and attribute change to
  particular mechanisms
• predict future climate change

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Types of model1

• There are 2 approaches of model
• empirical statistical based on extrapolation
  from previous climates that have occurred - cant
  predict anything new
• first principles based on fundamental
  mathematical equations governing fluid dynamics -
  can predict new situations

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Model validation

• Simulate present day climate
• Individual components such as radiation /
  convection
• Simulate past climates of Earth
• Simulate climates of other planets

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Hierarchy of models
0 dimensions (e.g. simple energy balance model)
Latitude - longitude (paleoclimate models)
Latitude - altitude (chemistry models)
3-D models
Coupled atmosphere/ocean models
slab ocean
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Types of experiments
Equilibrium response Perturb the atmosphere
and do a long simulation until energy balance us
restored at a new equilibrium, then record
temperature change. Can be done with a simplified
model.
Transient response Perturb the atmosphere and
examine the temperature as a function of time -
allows us to examine what happens at a given
time, but needs a good ocean and is more more
expensive.
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Temperature changes
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What might happen in the future

• Human influences will continue to change
  atmospheric composition throughout the 21st
  century (IPCC,2001)
• We can have most confidence in those changes
  predicted consistently by several different
  models.

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Future temperature changes

• Increases in global mean temperature of 1.4 - 5.8
  C by the year 2100
• Greater warming over land than over ocean,
  especially in North America and northern and
  central Asia during the cold season
• Probably an increase in number of hot days and
  decrease in cold days
• Night-time increase more than day-time

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T
Precip.
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Future sea level changes

• Rise by a further 0.09 to 0.88m by the year 2100
• Half of this rise comes from thermal expansion,
  remainder from melting glaciers and the Greenland
  ice sheet

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Other future changes1

• Increases in global averages and variability of
  both precipitation and evaporation (NH mid-lats
  more rain than snow)
• Increased summer heating decreases soil moisture
• recent trends for SST patterns to become more El
  Nino -like

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Other future changes 2

• Change in frequency and duration of extreme
  events
• Possible but very uncertain changes in weather
  events

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Impacts

• Increases in heatwaves - increase in mortality
  due to heat stress
• flooding
• coastal erosion
• agricultural yields decrease in places
• extension of desertification
• pressure on water resources
• spread of disease and pest to new areas

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The number of people at risk by the 2080s by the
coastal regions under the sea-level rise scenario
and constant (1990s) protection, showing the
regions where coastal wetlands are most
threatened by sea-level rise. (From Met Office)
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Percentage change in average crop yields for the
climate change scenario wheat, maize and rice.
(From Met Office)
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Change in natural vegetation type (From Met.
Office)
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Change in water stress, due to climate change, in
countries using more than 20 of their potential
water resources (From Met Office)
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Potential transmission of malaria a) baseline
climate conditions (1961-1990) b) climate
change scenario for the 2050s. (From Met
Office)
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Impacts for the UK

• Much harder to predict regional climate change
• Northwards shift of vegetation by 50-80km per
  decade
• impacts on wildlife, soils, water resources and
  agriculture in South

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Legislation

• Mitigation vs adaptation?
• To prevent any further rise in CO2 we would need
  to cut emissions by 60
• Can stressed ecosystems adapt fast enough?
• Migration is in many places impossible

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Timescale for future change
10s/100s yrs
100 years
100s / 1000 yrs
Stabilised CO2 concs in the atmosphere
Stabilised surface temperature
Stabilised sea level
Stabilised emissions
Any response to changes we make will be very slow.
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Kyoto Protocol

• Reduction of emissions of CO2, CH4, N2O and
  basket of 6 gases which includes SF6 and
  several of the HFCs
• Role of carbon sinks uncertain
• Ratification (particularly by US)?
• Role of developing nations?

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Measures for Kyoto Protocol

• Global Warming Potentials (accounts for strength
  and lifetime of greenhouse gases)
• Total Equivalent Warming Impact (TEWI)
• e.g. for a refrigerant

Effect of CO2 emission while using appliance
GWP of refrigerant GWP of insulator
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What have we found so far?

• Climate change is unlikely to be solely the
  result of either natural or anthropogenic effects
• Complexity is still an issue, especially
  interaction of biosphere and other components
• Can get good representation of past climate
  change using greenhouse gases and aerosols

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What is there still to do?

• Aerosols
• Biosphere feedbacks
• Regional climate change
• Parameterisations for climate models
• Real knowledge is to know the extent of ones
  ignorance
• Confucius

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Pollution 1

• Smog including ozone
• Particulates PM10
• Acid rain
• Heat
• (Noise)

Primary and secondary sources of pollutants
adverse effects of secondary pollutants are often
more severe
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Pollution 2

• Short -term and long-term risks from exposure
• Short-term eye irritation, asthma
• Long term strain on immune system, cancer
• Effects of anthropogenic pollution extend beyond
  the immediate urban area

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Pollution sources

• Combustion - CO2, CO, NOx, SO2, H2O unburnt
  hydrocarbons
• Emissions from cars are important in formation of
  photochemical smog
• Low temperature sources e.g. leakage from
  natural gas lines, evaporation of solvents,
  fertilisers, refrigerants and electronics
  industry
• Compared by emission factor

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Classical (or London) smog

• Smokefog - heavily polluted air in cities due to
  SO2 and aerosols from fossil fuel burning
• Infamous London smog of 1952 4 days and
  implicated in death of 4000 people (but may have
  been due to coincident low temperatures)
• very rare since air pollution regulations

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Formation of London smog
Fog droplets form on smoke aerosols
SO2 absorbs into these droplets
SO2 oxidised to form sulphuric acid
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Photochemical Los Angeles smog
From Hobbs (2000)
Hydrocarbons and NOx from vehicles sunlight
stagnant weather conditions
High concentrations of nitrogen oxides, ozone,
CO, aldehydes
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New winter smog

• High levels of NO2 resulting from vehicle
  emissions of NO, low temperatures and stagnant
  meteorology

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Pollution meteorology

• Usually the atmosphere can disperse even quite
  high emissions of pollutants
• Calm conditions, valleys and coastal areas are
  particularly at risk due to local circulations
• Vertical movement is controlled by temperature
  profile of atmosphere (e.g. inversions)

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Air pollution disasters
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Particulates, PM10

• Released again from fossil fuel burning (and dust
  associate with vehicles)
• Can stick to lung walls if inhaled (especially if
  charged particles)
• Concentrations are often higher inside cars in
  heavy traffic than by the side of the road due to
  air intake into cars.

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Acid rain

• Key environmental issue in 1980s
• Rainfall of very low pH value or dry deposition
  of acidic gaseous and particulate constituents
• Usually attributed to SO2 from fossil fuel
  burning or nitrogen oxide emissions and often
  falls at great distance from source
• Countries with high rainfall (e.g. Sweden) most
  at risk

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Other pollution

• Heat
• Noise
• indoor pollution
• global pollution (as in greenhouse gases etc)