Prof. Dudley Shallcross Atmospheric Chemistry Research Group 2012
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Transcript of Prof. Dudley Shallcross Atmospheric Chemistry Research Group 2012
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Prof. Dudley Shallcross Atmospheric Chemistry Research Group 2012
Air chemistry (outdoor and indoor)
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The Atmosphere: Pressure and Temperature
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3
O O O O
O O
O
O O
O
UV
UV
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4 The Chapman Mechanism
In the 1930s Sidney Chapman devised a mechanism that accounted
for the ozone layer and the temperature structure.
O2 + h O* + O*
O* + O2 + M O3 + M
O3 + h O2 + O*
O3 + O 2O2
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5Until 1964 the Chapman reactions were thought to be the principal processes governing the ozone balance in the stratosphere. However, measurements indicated that the actual concentration of ozone is smaller than that predicted by about a factor of two to four.
Predictions of ozone concentrations by the Chapman mechanism compared with observations at Panama, 1970.
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6Catalytic Ozone Destruction.
For a chemical to significantly affect the overall concentration of ozone it
either must be present in great abundance or must be involved in a catalytic
cycle. Breakthroughs in the 1970’s identified a number of NATURAL catalytic
processes that all have the form:
X + O3 XO + O2
XO + O X + O2
net : O3 + O 2O2
Where X = H, OH, NO, Cl or Br.
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7 CFCs: Molina and Rowland Nature 249, 810-812 (1974)
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8 Importance of reservoirs
If the catalysts carried on unabated they would
themselves destroy the ozone layer, but happily
there are termination reactions that lead to the
formation of reservoir species e.g.
Cl + CH4 HCl + CH3
ClO + NO2 ClONO2
Active (radicals) Inactive (reservoirs)
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The ozone hole27th Anniversary
Farman et al. Nature 1985
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What might have happened if we did nothing about CFCs?
Newman et al. Atm. Chem. Phys., 9, 2113 (2009)
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What might have happened if we did nothing about CFCs?
Newman et al. Atm. Chem. Phys., 9, 2113 (2009)
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12 Take home message
17% of globally averaged ozone gone by 2020
67% by 2065
Collapse of lower strat. tropical ozone by 2060
UV levels double by 2060
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13
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14 Air Pollution and the Troposphere10 km
NO, NO2, VOC
VOCs
halocarbons
0 kmCompounds of both biogenic and anthropogenic origin
1 km
The Tropopause
The Boundary Layer
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15
O3 + sunlight O * + O2 < ~ 330 nm
O* + H2O OH + OH
OH + R-H R + H2O
VOCs broken down by the OH radical,
generated by sunlight
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16 Ozone Chemistry- low NOx environment
Δ[O3]
[NOx]
Examples: Marine boundary layer, remote free troposphere
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17 Ozone Chemistry- low NOx environment
O3 + hν → O (1D) + O2 λ ≤ ~ 330 nm
O (1D) + M → O (3P) + M
O (1D) + H2O → 2 OH
CO + OH → CO2 + H
H + O2 + M → HO2 + M
HO2 + O3 → OH + 2O2
Net: CO + O3→ CO2 + O2
Δ[O3]
[NOx]
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18 Ozone Chemistry- higher NOx environment
Δ[O3]
[NOx]
Examples: Outflow from pollution centres and biomass
burning regions
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Ozone Chemistry- higher NOx environment
CO + OH → CO2 + H
H + O2 + M → HO2 + M
HO2 + O3 → OH + 2O2
NO + HO2 → NO2 + OH
NO2 + hν → NO + O(3P)
O(3P) + O2 + M → O3 + M
Net: CO + 2O2 → CO2 + O3
Δ[O3]
[NOx]
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Ozone Chemistry- higher NOx environment
CO + OH → CO2 + H
H + O2 + M → HO2 + M
HO2 + O3 → OH + 2O2
NO + HO2 → NO2 + OH
NO2 + hν → NO + O(3P)
O(3P) + O2 + M → O3 + M
Net: CO + 2O2 → CO2 + O3
Δ[O3]
[NOx]
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Ozone Chemistry- higher NOx environment
CO + OH → CO2 + H
H + O2 + M → HO2 + M
HO2 + O3 → OH + 2O2
NO + HO2 → NO2 + OH
NO2 + hν → NO + O(3P)
O(3P) + O2 + M → O3 + M
Net: CO + 2O2 → CO2 + O3
Δ[O3]
[NOx]
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NOx Limiting Environment
Δ[O3]
[NOx]
NO2 + OH → HNO3
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What about the indoor environment?
Three differences
1. No meteorology – slower movement of air (in
general) ventilation rates important
2. More surfaces (surface:volume ratio) deposition
and emission of chemicals much more important
3. Light levels very different (less UV indoors but
may have higher total light levels than outdoors?)
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1.Different ventilation rates
Some ideas from experiments in London
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Site features
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A BC
X2
X1D
KEY
Receptor Site 1-12
Receptor Site A-C
Tracer Release Points
Marylebone Rd.
Glo
ucester P
lace
DAPPLE #02– Summer 2004
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Comparison between rooftop and indoor site
0.0E+00
5.0E-06
1.0E-05
1.5E-05
2.0E-05
2.5E-05
3.0E-05
3.5E-05
4.0E-05
4.5E-05
5.0E-05
0 2 4 6 8 10
Bag No,
C/Q
Roo
ftop
.
0.0E+00
5.0E-07
1.0E-06
1.5E-06
2.0E-06
2.5E-06
3.0E-06
3.5E-06
4.0E-06
4.5E-06
5.0E-06
C/Q
Indo
or .
Rooftop
Indoor
Roof conc. approx 10 times greater than Indoor
Longer transport time to
Indoor position
Longer decay time
Results Indoor (2004)
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Ventilation rates
Mechanically ventilated –
sealed building, air sucked in and pumped out, regulated by levels of CO2. Outdoor air pumped in
but filtered to remove particles.
Naturally ventilated –
leaky buildings (most dwellings and many offices),
too hot, open a window, too cold, close off room.
Inevitable ingress of outdoor air.
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2. Emissions and deposition
1. Many chemicals released indoors are also
released outdoors but depending on confinement
and ventilation, exposure levels indoors may be
much much higher and last for much longer.
2. Typical sources indoors include; fabrics,
varnishes, paint, cooking, heating systems, air
fresheners! Cleaning products (with added scents)
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Some examples of chemicals indoors
• Paradichlorobenzene Moth crystals, room deodorants
• Methylene chloride Paint removers, solvent usage
• Formaldehyde Pressed wood products, foam
• Styrene Insulation, textiles, disinfectants, plastics, paints
• Acetaldehyde Glues, deodorants, fuels, preventives, mold
growth on leathers
• Acrolein Component of oak-wood, by-product of the
combustions of wood, kerosene and cotton
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Some examples of chemicals indoors
• Toluene diisocyanate Polyurethane foam, aerosols
• Benzene Smoking
• Tetrachloroethylene Wearing or storing dry-cleaned
clothes
• Chloroform Chlorinated water (showering, washing
clothes, dishes)
• 1,1,1-trichloroethane Wearing or storing dry-cleaned
clothes, aerosols sprays, fabric protectors
• Carbon tetrachloride Industrial strength cleaners
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Some examples of chemicals indoors
• Aromatic hydrocarbons (toluene, xylenes,
• ethylbenzene, trimethylbenzenes)
• Paints, adhesives, gasoline, combustion sources
• Aliphatic hydrocarbons
• (octane, decane, undecane)
• Paints, adhesives, gasoline, combustion products
• Terpenes (limoneme, α-pinene) Scented deodorizers,
polishes, fabrics, fabric softeners, cigarettes, food
beverages
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Some examples of chemicals indoors
• Alcohols Aerosols, window cleaners, paints, paint
thinners, cosmetics and adhesives
• Ketones Lacquers, varnishes, polish removers,
adhesives
• Ethers Resins, paints, varnishes, lacquers, dyes,
soaps, cosmetics
• Esters Plastics, resins, plasticizers, lacquers
solvents, flavours, perfumes
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3. Light levels
1. Glass will cut off high energy UV light from the
Sun and will reduce visible light levels. General
shading by buildings will also reduce light levels in
general.
2. All this means that Chemistry is much slower
indoors than outdoors but the build up can be
greater because of the slow air movement.