1. Christine Stevens Mike Thelen Nicole Verbiese
Use of Photochemical Ozone Creation Potential as a means of evaluating the contribution of volatile organic compounds to ground-level ozone concentrations
Christine Stevens
Mike Thelen
Nicole Verbiese

2. Presentation Outline
What are the drivers for increasing restrictions on Volatile Organic Compounds (VOCs)?
Role of VOCs in the ozone formation mechanism
VOC legislation in Europe; existing legislation
What is Photochemical Ozone Creation Potential (POCP)?
Use of the Photochemcial reactivity concept to gain exemption of Volatile Methyl Siloxanes (VMS) from US EPA VOC classification
POCP values of typical VMS
Why is it important that POCP becomes recognised as a means of evaluating VOCs in Europe
Conclusions
Acknowledgements

3. What are the drivers for increasing restrictions on VOCs?
Primary driver is to prevent the formation of ground-level ozone
Ozone can damage health & vegetation at high concentrations
Air Pollution by Ozone Directive (92/72/EEC) passed in Updated by Directive 2002/3/EC which sets a more stringent Alert Threshold to replace the Warning Threshold used in Directive 92/72/EEC and sets 120 µg/m3 as long term objective
Population Information Threshold (1 h average): 180 µg/m3 ozone
Population Alert Threshold (1 h average): µg/m "
Vegetation protection: µg/m “
VOCs in conjunction with oxides of nitrogen are a precursor for formation of ground-level ozone in the presence of sunlight

4. Role of VOCs in the ozone formation mechanism
AIR QUALITY
SUNLIGHT
UV: l nm
Troposphere
Ozone
Stratosphere
Ozone mixing
Sun
Light
50 km
10-16 km
0 km
UV: l
> 330 nm :
penetration to
Earth’s surface NO
+ O
NO + O 2 2 3 +
other
VOC + O
photochemical 2
reactants
Sea level
Biogenics
± 31%
“Mobile”
± 24%
Solvents
± 22%
Others
± 23%

5. Orange area – Concentrations exceed 240 µg/m3 Ozone Alert Threshold
European areas exceeding Ozone Thresholds in June 2002 (from European Centre on Air & Climate Change)
Key:
Yellow area – Concentrations exceed 180 µg/m3 Ozone Information Threshold
Orange area – Concentrations exceed 240 µg/m3 Ozone Alert Threshold
Examples of where hourly ozone concentrations have exceede 180 µg/m and 22 June 2002

6. Ozone concentrations in summer 2005
EU countries exceeding the Alert Threshold (240 µg/m3):
Austria, Belgium, Czech Republic, Estonia, Macedonia, Poland, Portugal, Slovak Republic, Slovenia, UK
EU countries exceeding the Information Threshold (180 µg/m3):
France, Germany, Greece, Netherlands, Spain, Switzerland
Most EU countries are exceeding Information Threshold limits during summer months.
Trend over recent years for average concentrations of ground-level ozone to increase
Global warming is expected to accelerate this trend

7. Other drivers
Clean Air for Europe (CAFE) programme – the objective is to protect against adverse effects of air pollution on human health and the environment. Included in 7th Framework Programme
SCALE (Science, Children, Awareness-raising, Legislation and Evaluation) programme) focuses on protecting children’s health. One of the main concerns is exposure to pollutants, including VOCs within buildings.
INDEX (Indoor Exposure Limits for Priority Pollutants) EU progamme
German NIK (Niedrigste Interessierende Konzentration) standard for emission limits from building materials (thereby having influence on indoor air)

8. VOC legislation in Europe
Integrated Pollution Prevention & Control (IPPC) Directive (96/61/EC) sets emission limits for various pollutants including organic carbon from large installations
Solvents Emissions Directive (1999/13/EC) (usually referred to as the VOC Directive) limits solvent emissions in a number of industrial sectors, but does not limit their use
National Emissions Ceilings Directive (2001/81/EC) sets emission limits for each Member State for four pollutants responsible for acidification, eutrophication & ground-level ozone pollution, namely, VOCs, sulphur dioxide, nitrogen oxides, and ammonia
VOCs in Paints, Varnishes and Vehicle Refinishing Products Directive (2004/42/CE)

9. What is Photochemical Ozone Creation Potential?
POCP is an indicator of the ability of a VOC to contribute to photochemical ozone formation
A measure of the reactivity of an organic compound with hydroxyl radicals & subsequent formation of ozone
VOCs vary in their reactivity & therefore contribute differently to the formation of ozone
Concept developed by Derwent and Jenkin in 1990’s who incorporated POCP into photochemical trajectory models

10. Use of the POCP concept by Regulatory Authorities in other geographic areas
Used by the US Environmental Protection Agency as a basic measure to compare reactivities of volatile compounds
Maximum Incremental Reactivity (MIR) – scheme developed in the US & used by California Air Resources Board (CARB); calculated for reference scenarios based on:
Specified meteorological conditions
Initial pollutant concentrations
Emission rates of NOX & VOC

11. Use of POCP concept to gain exemption of Volatile Methyl Siloxanes (VMS) from US EPA VOC classification
US EPA definition of a VOC is any carbon compound, which reacts photochemically in the atmosphere*. Methane & ethane which have negligible photochemical reactivity are the base line for comparison.
As volatile methyl siloxanes (VMS) do not deplete stratospheric ozone, Dow Corning successfully petitioned US EPA in 1994, for an exemption of VMS from US VOC regulations for use as chlorofluorocarbons (CFCs) substitutes (specifically precision & electronic cleaning applications)
Subsequent to this, VMS were exempted from regulation as VOCs, permitting their use as replacements for CFCs in a range of industrial and consumer products
* This differs fundamentally from the EU definition defined in the Solvents Directive where a VOC is any organic compound with a vapor pressure ≥ 0.01 kPa at 20ºC, i.e. no account is taken of reactivity

12. Volatile Methyl Siloxanes – smog chamber study
Environmental chamber experiments performed by University of California (Atkinson, 1991; Carter,1992)
Studies consisted of 6 h irradiation of smog precursors with & without VMS in the presence of high & low concentrations of NOX
VMS tested:
Hexamethyldisiloxane (HMDS)
Octamethylcyclotetrasiloxane (D4)
Decamethylcyclopentasiloxane (D5)
Pentamethyldisiloxanol (hydroxylated degradation product of HMDS)
VMS were found to make no contribution to photochemical ozone formation

13. Incorporation of POCP values for VMS into European Photochemical Trajectory Model
POCP Trajectory model developed by Derwent and Jenkin (1990, 1991) used to predict POCP values of VMS for three trajectories over Europe
Trajectory 1: traverses southern England and simulates 1 day’s photochemistry across downwind of London, travelling in a westerly direction
Trajectory 2: traverses Germany, Belgium, UK and Ireland, simulating 4 days’ photochemistry, travelling in a westerly direction
Trajectory 3: traverses France, Belgium, Netherlands, Germany, Denmark & Sweden, simulating 4 day’s photochemistry, travelling in a northerly direction
POCP values calculated by Derwent and Jenkin vary from -1.6 to 0, and the results were compared with ethylene (on a scale where ethylene = 100)

14. POCP values of VMS expressed relative to ethylene*
Traject-ory
Southern England
Germany→Ireland
France→Sweden
Mean
Day 1 2 3 4
Ethylene
100
HMDS
-0.3
-0.2
-0.1 D4
-0.6
-0.4
-0.5 D5
0.0
MDOH
* Ethylene is a very strong precursor for the formation of ground-level ozone

15. Why is it important that POCP becomes recognised as a means of evaluating VOCs in Europe
Despite the introduction of legislation limiting VOC emissions in Europe, average ozone levels are gradually increasing.
The focus by the EU Commission is therefore shifting to consumer market segments as illustrated by the recent Directive (2004/42/CE) on VOCs in Paints, Varnishes and Vehicle Refinishing Products Directive & the ongoing review by IVAM (Netherlands) on use of VOCs in personal care products.
The use of low-POCP VOCs is a more focused approach which can be used in order to meet the increasingly stringent regulations on ozone, while at the same time permitting the continued use of valued consumer products in the market place.

16. Conclusions
Current “mass-based” legislation in Europe does not distinguish between the reactivity of different VOCs in terms of ozone creation potential
If further VOC reduction measures are to be considered, then replacing highly reactive VOCs with less reactive VOCs could be a more focused, cost-effective approach
In the US, the use of volatile methyl siloxanes was successfully used as an alternative to reduce the regulated VOC content of a product
The use of volatile methyl siloxanes with zero (even negative) Photochemical Ozone Creation Potential should be considered as one means of meeting ever more stringent ground-level ozone regulations in Europe

17. Acknowledgements
This work was sponsored by Dow Corning Corporation