Prof. Dudley Shallcross Atmospheric Chemistry Research Group 2012

Air chemistry (outdoor and indoor)

2

The Atmosphere: Pressure and Temperature

3

O O O O

O O

O

O O

O

UV

UV

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

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.

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.

7 CFCs: Molina and Rowland Nature 249, 810-812 (1974)

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)

The ozone hole27th Anniversary

Farman et al. Nature 1985

10

What might have happened if we did nothing about CFCs?

Newman et al. Atm. Chem. Phys., 9, 2113 (2009)

11

What might have happened if we did nothing about CFCs?

Newman et al. Atm. Chem. Phys., 9, 2113 (2009)

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

13

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

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

16 Ozone Chemistry- low NOx environment

Δ[O3]

[NOx]

Examples: Marine boundary layer, remote free troposphere

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]

18 Ozone Chemistry- higher NOx environment

Δ[O3]

[NOx]

Examples: Outflow from pollution centres and biomass

burning regions

19

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]

20

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]

21

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]

NOx Limiting Environment

Δ[O3]

[NOx]

NO2 + OH → HNO3

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?)

1.Different ventilation rates

Some ideas from experiments in London

Site features

1

2

3

4

5 6

7

9

8

10

11 12

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

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)

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.

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)

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

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

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

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

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.