Air Pollution Miljmtteknik FKF100 vt2009 Part 3

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Air PollutionMiljömätteknik FKF100 vt-2009Part 3

• Erik Swietlicki
• Professor
• Div. of Nuclear Physics, Physics Department
• Lund University Lund Institute of Technology
• Erik.Swietlicki_at_nuclear.lu.se

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Atmospheric chemistry
The troposphere is a chemical reservoir that is
fairly well separated from the stratosphere. The
mixing time in the troposphere is 1-2 months
within each hemisphere. Chemical substances with
a lifetime shorter than 1 year are transformed
within the troposphere.
Horizontal mixing
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Ground-Level OzonePhotochemical smog
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Photostationary equlibrium for ozone
In a sunlit atmosphere with NO and NO2 but
without hydrocarbons (11.11) NO2 hn ?
NO O (?lt 420 nm) (10.2) O O2 M ?
O3 M (only way to produce O3) (11.14)
NO O3 ? NO2 O2 Net reaction
A photostationary
equilibrium exists. More sun light (?lt 420 nm)
gives more ozone O3. NO consumes ozone. In the
vicinity of strong sources of NO, then O3 is
titrated out and can be entirely depleted (e.g.
close to a smoke stack or the tail pipe of a car.)
hn NO2 O2 ? NO O3
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Oxidation of hydrocarbons
O2
Hydrocarbons are combusted in the presence of
nitrogen oxides NOX under solar radiation and
results in O3 formation.
hn
NO
NO2
O3
hn
H2O
HO2
OH
Fast radical chemistry
Combusted fuel
O2
Fuel
O2
(hydrocarbons)
RO
(oxidized hydrocarbons)
RO2
O3
NO2
NO
hn
O2
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Ground-Level Ozone Production
Hydrocarbons are needed to shift the equilibrium
to the right, i.e. towards an increased ozone
production. Hydrocarbons consume NO (by producing
the peroxy radicals HO2 and RO2 that in turn
react with NO). More sunlight (?lt 420 nm) results
in more ozone O3.
hn NO2 O2 ? NO O3

• Prerequisites for high levels of ozone
• Sunlight (?lt 420 nm)
• Hydrocarbons
• Nitrogen oxides (NOX)

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Hydrocarbon (VOC) emissions 1997 (EMEP)
Unit tonnes NMVOC
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Ground-Level Ozone Background Levels in Southern
Sweden
http//www.ivl.se/miljo/projekt/ozon/ http//www.e
ea.europa.eu/maps/ozone/map
Daily averages and highest hourly averages in
southern Sweden Station Vavihill (Söderåsen) 2006
Inform the public
Highest hourly average
Health effects
Daily average
Crop damages
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1 ppb ozone 2 µg/m3
Updated 2007
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Air Quality Background Monitoring Station
Vavihill, Söderåsen
LU PM10, PM2.5, Climate-related aerosol
properties IVL EMEP-station, ozon
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Hemispheric background levels of ground-level
ozone have increased by 5 ppb per decade the
last 20-30 years.
Data from the station Mace Head on the west coast
of Ireland.
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Trends in ground-level ozone in Swedish
background air
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Ground-level ozone Photochemical smog
In polluted environments (e.g. large cities),
concentrations of hydrocarbons, nitrogen oxides,
ozone and aerosol particles often follow a
certain diurnal pattern.
Hydrocarbons
Oxidized and nitrated hydrocarbons
Aerosol particles

NO
NO2
O3
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Ozone Damages on Crops
Crop yields decrease with increased accumulated
exposure to ozone above the threshold 40 ppb
(AOT40). AOT40 should be lt 3000 ppb?h (5
decrease in crop yield).
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AOT40 based on the RAINS model
AOT40 (ppm?h)
for 1990 emissions
Emissions according to the Gothenburg protocol
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Transboundary Acidification, Eutrophication and
Ground Level Ozone in Europe, EMEP Report 12
2002, http/ /www.emep.int
Growing crops take up ozone through their stomata
(klyvöppningar)
AOT40 quantifies ozone exposure, not ozone
uptake. Southern Europe High ozone levels but
dry climate ? Stomata closed (klyvöppnigarna
stängda) ? Less ozone uptake
Estimated ozone uptake by growing crops through
the stomata, June (nmol m-2 s-1)
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Acidification
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Acidification
Sulphur- and nitrogen-containing compounds are
oxidized in the atmosphere and are transferred
from the gas phase to solid or liquid phase in
the form of aerosol particles or cloud droplets.
The sulphur and nitrogen is then in the form of
sulphates and nitrates. Th acidic aerosol
particles and cloud droplets are deposited mainly
as acid rain (wet deposition). The low levels of
SO2 found in Sweden today are not a threat to
human health. Concentrations of aerosol
particles (containing sulphates and nitrates) are
close to new PM air quality limit values. The
acid deposition is still higher than what our
ecosystems can endure in the long term (critical
load).
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Aqueous Phase Oxidation of Sulphur
S(IV) dissolves in aqueous solutions
SO2(g) ? SO2?H2O ? HSO3- H ? SO32- 2H
S(IV) in aqueous solutions is often in the form
of HSO3- (bisulfite ion).
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Aqueous Phase Oxidation of Sulphur

• S(IV) is oxidized in aqueous solution
• Via hydrogen peroxide H2O2
• HSO3- H2O2(aq) H ?
• 2H SO42- H2O
• Via ozone O3
• S(IV) O3(aq) ?
• S(VI) 2H O2
• Catalyzed by transition metals
• (e.g. Mn, Fe) at night, winter-time.

(?SO2 1 week).
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Exchange between phases
HNO3
NH3
Organic compounds with low vapour pressures
NO3-
NH4
HCl
Cl-
OC
H
H2O
SO4
H2O
SO2
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Emissions of sulphur dioxide 1997 (EMEP)
Unit tonnes of SO2
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EMEP Eulerian Acid Deposition model - Sulphur
(1997)
SO2
SO42-
Sulphur deposition to Sweden
Sulphur deposition
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Critical load Acidification, eutrophication
Definition (Nilsson and Grennfelt, 1988) The
threshold below which significant harmful effects
on specified sensitive elements of the
environment do not occur according to present
knowledge is called the critical load. Critical
load (acidification, eutrophication) Represents
a deposition that is sutainable in the long
term. Can be expressed in various ways. E.g.
2-percentile for critical load is the deposition
of acidifying (or eutrophying) compounds at which
98 of all ecosystems are protected in the long
term.
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Critical Load
The critical load for acidification given as
the 2- percentile (protects 98 of all
ecosystems) (equivalents / ha / year) Nordic
soils are very sensitive. Mediterranean soils are
quite insensitive to acid deposition.
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Exceedance of Critical Load
(Unit of ecosystems, Scale 0-100)
For emissions according to the 1999 Gothenburg
protocol
For emissions 1990