1. Hemispheric Ozone and Cooperation
Terry J. Keating, Ph.D.
U.S. EPA
Co-chair TF HTAP
Frank Dentener, Ph.D.
European Commission JRC
Co-chair TF HTAP
Air Science Policy Forum, Dublin, 15.04.2013

2. Why do we worry about hemispheric tropospheric ozone?
•Ground-level ozone is one the most harmful air pollutants in Europe
•Levels continue to exceed air quality thresholds (EEA, 2011)
•New evidence of health impacts of ozone at lower levels
•Ozone is also damaging crops and natural vegetation
•Tropospheric ozone is an important climate forcer (ca. 0.4 Wm-2 )
•Hemispheric ozone is changing.
2

3. Lower troposphere
Mid-upper troposphere
Pathways of transport hemispheric
air pollution
Stohl et al, 2004
3

4. • Change in global baseline O3?
• Changes were stronger in 1990s
than in 2000s
• What is the role of changing
global emissions and climate?
• How does this impact air quality
in Europe?
• Is this happening everywhere
along the borders of Europe?
Courtesy D. Derwent, K. Law, D Parrish
What is causing the change in O3
between 1989-1994 and 2006-2010?
Ozone at Mace Head, Ireland
4

5. IPCC AR5 courtesy O. Cooper, 2013
Global baseline ozone changes between 1990s
and 2010
5

6. • Established in 2004 by the UNECE
Convention on Long-Range Transport Air
Pollution
• Co-chaired by the European Commission
and the U.S. EPA
• An expert group of scientists studying
hemispheric transport of air pollution
• HTAP Phase 1: HTAP Assessment report
2010
• HTAP Phase 2: by 2015 targeted
briefings, reports and publications
What is HTAP?
6
www.htap.org

7. •Examine transport of air pollution across the Northern
Hemisphere, including ozone (precursors) and PM and components
(including black carbon), mercury, and persistent organic
pollutants.
•Assess potential emission mitigation options available inside and
outside the UNECE region
•Assess their impacts on regional and global air quality,
public health, ecosystems, near-term climate change
•Collaboration with other groups both inside and outside the
Convention
Mandate
7

8. NA
EU
EA
SA
HTAP (2010) Multi-Model Experiments
Source-Receptor Sensitivity Simulations:
•Base Year 2001
•More than 30 global models from Europe, US and Asia
•Decrease emissions of precursors in each region by 20%
•Precursors emission combinations NOx, VOC, CO, CH4, Hg, POPs
8

9. Total O3
change
Within EU
Outside of EU
Methane
HTAP reconstruction of O3 changes in
Europe: attribution of drivers.
NA
EU
EA
SA
• Annual average - large region –global models
• Largest O3 (6 ppb) decreases before 1980; small
reductions in O3 during 1980-2000
• O3 reductions attributable to EU emissions
compensated by increasing emissions elsewhere
• Important role for (global) CH4 30-50 %
• Taken together changes in O3 from outside
Europe and CH4 are larger than within EU (60-70
% of total)
• External O3 becomes more important when
‘local’ sources are more regulated.
• Hemispheric transport more important at ‘lower’
concentrations
Wild et al, ACP, 2012
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10. 10
European annual regional mean O3 changes [ppb] for a range
of future global air pollution scenarios
Wild et al, in prep. 2013
SRES A2
RCP 8.5
RCP 2.6

11. 1. Emissions &
Projections
2. Source/Receptor &
Source Apportionment 3. Model/Observation &
Process Evaluation
4. Impacts on Health,
Ecosystems, & Climate 5. Impact of Climate
Change on Pollution
6. Data Network & Analysis Tools
Policy-RelevantScience
Products&Outreach
TF HTAP: Themes of Cooperative Activities 2012-2016

12. 12
• An improved modeling system based on ensembles of regional and
global models that reflect our current best knowledge on the
intercontinental transport of air pollution and its impacts on health,
ecosystems and climate under past-present and future conditions.
• An evaluation of the potential for mitigation of large scale air
pollution problems under future emission scenarios, considering
various alternatives at the country, regional and global level,
anchored by a set of consistent and plausible benchmark scenarios
developed by IIASA and an understanding of possible changes in
emission drivers.
• Enhanced global scientific cooperation to develop models, methods,
and measurements to improve our understanding of the role of
hemispheric air pollution and its impacts.
Perspectives for TF HTAP Phase: 2015

13. 13
• To better understand hemispheric O3 transport, long-term, high
quality monitoring of O3 and related components at strategic
(inflow) locations in Europe are indispensable.
• Scientific assessments show that the contribution of hemispheric O3
to local pollution is increasing.
• Increasing hemispheric pollution necessitates greater and more
expensive controls at the local or national level to achieve the same
air quality objectives and justifies efforts to cooperate on a
hemispheric or global scale to reduce tropospheric ozone.
• The issue is being addressed by UNECE CLRTAP- with full support of
the EC and the US EPA, elsewhere the TF HTAP is an important
instrument to raise awareness.
• A portfolio of options is emerging- it is clear that emission reduction
of CH4 (producing O3) is going to be very important- with links to
co-benefits from climate policies.
Take home messages