Prof. Dudley Shallcross Atmospheric Chemistry Research Group 2012

1. Prof. Dudley Shallcross Atmospheric Chemistry Research Group 2012 Air chemistry (outdoor and indoor)

2. The Atmosphere: Pressure and Temperature

3. UV O O O O O O O O O O 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

5. Until 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.

6. Catalytic 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)

9. The ozone hole 27th 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

14. Air Pollution and the Troposphere 10 km The Tropopause The Boundary Layer 1 km NO, NO2, VOC VOCs halocarbons 0 km Compounds of both biogenic and anthropogenic origin

15. VOCs broken down by the OH radical, generated by sunlight O3 + sunlight O * + O2  < ~ 330 nm O* + H2O OH + OH OH + R-H  R + H2O

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 20 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 21 Δ[O3] [NOx]

22. NOx Limiting Environment Δ[O3] [NOx] NO2 + OH → HNO3

23. What about the indoor environment? Three differences • No meteorology – slower movement of air (in general) ventilation rates important • More surfaces (surface:volume ratio) deposition and emission of chemicals much more important • Light levels very different (less UV indoors but may have higher total light levels than outdoors?)

24. Different ventilation ratesSome ideas from experiments in London

25. Site features

26. DAPPLE #02– Summer 2004 Gloucester Place Marylebone Rd.

27. Results Indoor (2004) Roof conc. approx 10 times greater than Indoor Longer transport time to Indoor position Longer decay time

28. 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.

29. 2. Emissions and deposition • 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. • Typical sources indoors include; fabrics, varnishes, paint, cooking, heating systems, air fresheners! Cleaning products (with added scents)

30. 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

31. 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

32. 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

33. 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

34. 3. Light levels • 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. • All this means that Chemistry is much slower indoors than outdoors but the build up can be greater because of the slow air movement.