Transcript 3280 – Atmospheric chemistry

Atmospheric chemistry
Day 5
Ozone and air quality
Air quality and climate change
Impact of air pollution
UK Air Quality Strategy, 2007
• “Air pollution is currently estimated to reduce the life
expectancy of every person in the UK by an average of
7-8 months. The measures outlined in the strategy
could help to reduce the impact on average life
expectancy to five months by 2020, and provide a
significant step forward in protecting our
environment.”
•
Defra estimate the health impact of air pollution in
2005 cost £9.1–21.4 billion pa.
Air Quality Standards:
Ozone
• European Union Limit Value: Target of 120μg.m-3 (60
ppb) for an 8 hour mean, not to be exceeded more
than 25 times a year averaged over3 years. To be
achieved by 31 December 2010.
• UK Air Quality Objective: Target of 100μg.m-3 (50
ppb) for an 8 hour mean, not to be exceeded more
than 10 times a year. To be achieved by 31 December
2005.
Timescales of ozone chemistry
1. Global chemistry. Dominated by NOx + CH4 + sunlight.
Timescales are long as are transport distances.
2. Regional chemistry. Many VOCs are emitted, e.g. over
Europe. Each has its own lifetime governed by its rate
constant for reaction with OH. The timescales of
ozone production takes from hours to days. The
transport distance for a wind speed of 5 m s-1 and a
lifetime of 1 day is ~500 km.
3. Urban chemistry: high concentrations of NO from
transport sources. Ozone is depressed by the
reaction:
NO + O3  NO2 + O2
01/04/2006
01/04/2005
01/04/2004
01/04/2003
01/04/2002
01/04/2001
01/04/2000
01/04/1999
01/04/1998
01/04/1997
01/04/1996
01/04/1995
01/04/1994
01/04/1993
01/04/1992
01/04/1991
01/04/1990
01/04/1989
01/04/1988
01/04/1987
Monthly mean baseline ozone, ug/m3
Ozone mixing ratios at MaceHead
W. Ireland, under westerly airflows
110
100
90
80
70
60
50
40
Local effects – Ozone depression due to
reaction with high concentrations of NO in
London. Transect of ozone concentrations
70
Annual Mean Concentration (in
-3
g m )
60
50
40
30
20
10
0
465000
475000
485000
495000
505000
515000
525000
535000
545000
555000
Easting
PCM 2003
2003 AURN measurements
Ascot Rural
ADMS-Urban 2003
565000
575000
585000
Radiative Forcing
• Radiative forcing: the change in the net radiation balance at the
tropopause caused by a particular external factor in the absence
of any climate feedbacks.
• These forcing mechanisms can be caused by:
– change in the atmospheric constituents such as the increase
in greenhouse gases (GHGs)
– aerosols due to anthropogenic activity,
– changes in other components of the Earth/atmosphere
system such as changes in the surface albedo (the fraction
of incoming radiation that is reflected). Albedo changes are
caused, e.g., by changesin vegetation (e.g. burn scars or
agriculture).
Mechanisms of the radiative forcing
due to greenhouse gases and of the direct radiative forcings due to
aerosols
Global-average radiative forcing (RF) estimates and ranges in 2005
(relative to 1750) for anthropogenic GHGs and other important
agents and mechanisms
Carbon dioxide and methane mixing ratios versus time
(NOAA Climate Monitoring and Diagnostics Laboratory
http://www.cmdl.noaa.gov/ccgg/insitu.html)
Other GHGs
• N2O mixing ratios show an increase from a preindustrial value of around 270 ppb (Prather et al.,
2001) to 318 – 319 ppb in early 2004
• CFC-11, CFC-12, CFC-13, HCFC-22, and CCl4
concentrations increased from a pre-industrial value
of zero to 268 ppt, 533 ppt, 4 ppt, 132 ppt, and 102
ppt respectively (1998 concentrations) - leads to
radiative forcings of 0.07 W m-2, 0.17 W m-2, 0.03 W
m-2, 0.03 W m-2 and 0.01 W m-2
• Ozone: approximate doubling of concentrations
between the pre-industrial and present day.
Climate System
Schematic description of an ocean atmosphere general
circulation model
Evolution of models
Carbon cycle
Processes in an atmospheric chemistry model
Sulfur cycle
Sulfur emissions
Sulfur emissions 1860 - 1990
UK Air quality – comparison of trends in pollutants
relative annual mean concentration
120
100
80
60
40
SO2
PM10
CO
NOx
NO2
20
0
1997
1998
1999
2000
2001
Year
2002
2003
2004
Relative annual mean concentration (monthly intervals): selection
of monitoring sites in London.
AQEG PM report
Global NOx and CH4 emissions scenarios
200.0
160.0
NOx
120.0
80.0
40.0
0.0
1990
2000
Europe
Asia + Oceania
Africa + Middle East
SRES A2 - World Total
2010
2020
2030
North America
Latin America
Maximum Feasible Reduction (MFR)
SRES B2 - World Total
600
500
CH4
400
CLE - current legislation
SRES – IPCC analyses
MFR – maximum feasible
reduction
300
200
100
0
1990
2000
Europe
Asia + Oceania
Africa + Middle East
SRES A2 - World Total
2010
2020
North America
Latin America
Maximum Feasible Reduction (MFR)
SRES B2 - World Total
2030
•
•
•
•
•
•
•
SRES (IPCC Special Report on Emission Scenarios) scenarios
The A1 storyline is for a future world with very rapid economic
growth, global population that peaks in mid-century and declines
thereafter, the rapid introduction of new and more efficient
technologies and with a substantial reduction in regional
differences in per capita income. Within this family are three
sub-scenarios with different technological emphasis:
A1FI – A1, fossil fuel intensive
A1T – A1, with non-fossil energy source emphasis
A1B – A1, with a balance across energy sources.
The A2 storyline is a more pessimistic scenario, describing a
very heterogeneous world based on self-reliance, regional
differences in economic and technological development and
continuous increase in global population.
The B1 storyline describes a convergent world like A1, with
global population peaking in mid-century, but with rapid changes
in economic structures, introduction of clean and resourceefficient technologies, emphasis on global solutions to social and
environmental sustainability.
The B2 storyline describes a world with emphasis on local
solutions to social and environmental sustainability, less rapid
and more diverse than in B1 and A1, with continuously increasing
global population, but at a lower rate than A2.
Royal Society Report on ozone over next 100 years
Level of automobile emission limits in Asian countries, compared
with the EuropeanUnion. Source: Clean Air Initiative for Asian cities
Impact of improved technologies in Asian countries on
assessment of NOx emissions
New estimates of CO emissions
New estimates of CH4 emissions
Predicted lobal temperature rise for different
scenarios
Surface O3 (ppbv) 1990s
Change in surface O3, CLE 2020s-1990s
No climate change
CLE
+2 to 4 ppbv over
N. Atlantic/Pacific
>+10 ppbv
India
A large fraction is
due to ship NOx
BAU
ΔO3 from climate change
Warmer temperatures
&higher humidities
increase O3destruction
over the oceans
O3 + hn O1D + O2
O1D + H2O  2OH
O1D + N2, O2  O3P
But also a role from
increases in isoprene
emissions from
vegetation &changes in
lightning NOx
OH+RH(+O2)
 RO2 + H2O
RO2 + NO RO + NO2
NO2+ hn(+O2)NO+O3
2020s CLEcc2020s CLE
Atmospheric oxidation of
Termination
CH4 removed
mainly by reaction
with OH
O
3
NO2
CH4
NO2
OH
O3
NO
CH3O2
HO2
HO2
NO
Low NOx route
Ozone destruction
(background atmos)
Yield of OH and loss of
O3 depend on humidity
light
H2O
Termination
O1D +H2O 2OH
O1D +N2,O2 O3P

methane
O3
NO2
O3
Termination
HO2
High NOx route
Ozone formation
Polluted atmos
PAN – peroxy acetyl nitrate
PAN is formed from reactions of the acetyl peroxy radical and NO2:
e.g. CH3CHO + OH (+O2)  CH3COO2 + H2O
CH3COO2 + NO2
CH3COO2NO2 (PAN)
PAN is a reservoir compound
for nitrogen oxides and
provides a mechanism for their
transport, especially in the
upper troposphere. It provides
a means of carrying nitrogen
oxides from polluted to less
polluted regions. It is a major
player in the intercontinental
transport of pollutants
Impact of climate change on air quality - ozone
Heat wave in Europe, August 2003
• Monitoring stations in
Europe reporting high
band concentrations of
ozone
• >15 000 ‘excess deaths’
in France; 2000 in UK,
~30% from air
pollution.
• Temperatures
exceeded 350C in SE
England.
• What about Hungary?
• How frequent will such
summers be in the
future?
ozone / microg/m3
Budapest, 1 – 31 August 2003
200
180
160
140
120
100
80
60
40
20
0
Széna tér
Baross tér
Pesthidegkút
Kőrakás park
Laborc u.
0
100
200
300
400
time
500
600
700
800
NO2 in Budapest and
Hungary in 2005
Diurnal variation
13th August 2003
Pesthidegkut
ozone/ microg/cm3
200
150
100
Ser i es1
50
0
-1
4
9
14
time of day
19
24
Future summer temperatures
2003: hottest on record (1860)
Probably hottest since 1500.
15 000 excess deaths in Europe
Using a climate model
simulation with
greenhouse gas emissions
that follow an IPCC SRES
A2 emissions scenario,
Hadley Centre predict
that more than half of all
European summers are
likely to be warmer than
that of 2003 by the
2040s, and by the 2060s
a 2003-type summer
would be unusually cool
Stott et al. Nature, December 2004
Emission of biomass smoke from Portugal in August
2003: effects on local albedo