Transcript The Pollution-Climate Connection

Linking climate change and air quality: Results from a
pilot study.
Harmful components of smog:
• ozone
• aerosol (a.k.a. Particulate
matter, PM)
Collaborators:
Daniel Jacob, Shiliang Wu, Brendan Field
GISS: David Rind
Caltech: John Seinfeld, Hong Liao
U. Tennessee: Joshua Fu, Zuopan Li
Argonne: David Streets
Tropospheric ozone columns seen from GOME satellite, June 7-8, 1997
We know that day-to-day weather affects the severity and duration of
pollution episodes.
New England
days
Number of summer days with 8-hour ozone
> 84 ppbv, average for northeast U.S. sites
1988, hottest
on record
Probability
of ozone exceedance
vs. daily max. temperature
Lin et al. 2001
Why does probability of ozone episode increase with increasing temperature?
Faster chemical reactions, increased biogenic emissions, and stagnation.
How will a changing climate affect pollution?
Answer: we don’t know.
Rising temperatures could mean faster chemical reactions. . O3, PM
Higher surface temperatures could also mean a deeper boundary layer,
diluting concentrations at the surface. O3, PM
The picture is complicated.
Top of boundary layer
Soup of
pollution
precursors
{
ozone, aerosol
strong mixing
How to make pollution:
Need sunlight, water vapor, and a mix of
anthropogenic or natural “ingredients.”
H2O
Hydroxyl (OH)
winds
Ozone (O3)
+
Nitrogen oxides
CO, Hydrocarbons
rainout
(important for
aerosols)
deposition
Fires
Biosphere
Human
activity
Many meteorological variables affecting
pollution are sensitive to climate change.
How to make pollution:
Need sunlight, water vapor, and a mix of
anthropogenic or natural “ingredients.”
H2O
Hydroxyl (OH)
winds
Ozone (O3)
+
Nitrogen oxides
CO, Hydrocarbons
What will
people do?
rainout
(important for
aerosols)
deposition
Fires
Biosphere
Human
activity
Many meteorological variables affecting
pollution are sensitive to climate change.
GCAP Project: Global climate and air pollution study
GISS general circulation model, changing GHGs
1950 Spin-up
2000
2025
2050
archive temperatures,
humidity, winds, etc
precursor
emissions
GEOS-CHEM
global chemistry model
2075
2100
MM5
mesoscale
model
archive
chemistry
CMAQ regional
chemistry model
Why so many models? How do these models work?
All the models cut up the
atmosphere into gridboxes and
describe exchange of air mass,
and water vapor, chemical
species between boxes.
More boxes = more CPU time.
Feedbacks between chemistry
and climate require “on-line
chemistry” or iteration between
models.
Uncertainties: cloud feedbacks, land
cover effects, ocean circulation, abrupt
climate change, CO2 uptake.
Pilot project: We focus on future changes
in just winds (circulation) and rainout.
H2O
Hydroxyl (OH)
winds
Ozone (O3)
+
Nitrogen oxides
CO, Hydrocarbons
rainout
(important for
aerosols)
deposition
Fires
Biosphere
Human
activity
Pilot Project: Implement “tracers of anthropogenic pollution” into simpler
version of GISS General Circulation Model
Timeline
1950
spin-up (ocean adjusts)
2000
increasing A1 greenhouse gas
2050
Goddard Institute for Space Studies GCM: 9 layers, 4ox5o horizontal grid, CO2
+ other greenhouse gases increased yearly from 2000 to 2050.
July global mean temperature
Carbon Monoxide: COt
source: present-day anthro emissions
sink: CO + present-day OH fields
2045-2052
+2o C Temp change
spin up
Sensitive to climate change
Circulation also sensitive to climate change
{
Black Carbon: BCt
source: present-day anthro emissions
sink: rainout
19952002
Anthropogenic emissions:
• What changes:
Well-mixed greenhouse gas
concentrations over time
Climate response to greenhouse
gas trends, including rainout of
black carbon tracer
CO emissions (molecules /s)
• What remains the same:
Emissions of CO and black
carbon tracers
Sink of CO (monthly mean,
present-day OH)
BC emissions (kg/s)
Timeline
1950
spin-up (ocean adjusts)
2000
increasing A1 greenhouse gas
2050
Our approach: Look at daily mean concentrations averaged over
specific regions for two 8-year intervals (1995-2002) and (2045-2052).
Histogram of COt concentrations
averaged over Northeast for
1995-2002 summers (July-Aug)
midwest
California
northeast
southeast
Cumulative probability plot shows the
percentage of points below a certain
concentration.
Frequency distributions for surface COt and BCt show significantly
higher extremes in 2050s compared to present-day.
July - August
2045-2052
1995-2002
Changes at the extremes are due solely to changes in circulation and rainfall.
Frequency distributions for two U.S. regions in July-August show increased
severity of pollution episodes.
2050
2000
Daily COt and BCt
concentrations
correlate (R2 ~ 0.6 –
0.8) so much of the
difference is likely
due to changes in
circulation.
How does depth of boundary layer change with changing climate?
Maximum boundary layer heights.
2045-2052
Triangles
indicate days
of high
pollution.
1995-2002
Higher BL heights in future go in opposite direction to what is needed to
explain air quality differences.
Evolution of a typical pollution event. This happens repeatedly
during summertime.
weak winds
cyclone (low pressure system)
BCt and wind
fields for 6
consecutive days
in summer.
cold front from
Canada
We found 20%
decrease in
summertime
cyclone frequency
in future climate.
100 x mg/m3
A decrease in cyclone frequency over midlatitudes has also been
observed in recent decades.
1000
cyclones
Agee, 1991
500
100
1950
anticyclones
1980
annual number of surface
cyclones and anticylones for
North America and nearby
ocean
McCabe et al., 2001
30-60N
Standardized departure of
cyclone frequency over
Northern Hemisphere.
Model studies of future climate have
found similar declines relative to the
present-day. (e.g., Zhang and Wang, 1997;
Carnell and Senior, 2001; Geng and Sugi,
2003)
Two mechanisms for the meridional transport of energy on a round,
wet world.
1. Mid-latitude cyclones push warm
air poleward ahead of front, push
cold air equatorward behind front.
warm tropics
cold poles
cold front
2. Eddy transport of latent heat
carries energy to higher latitudes.
Reasons for decline in cyclone generation over midlatitudes in the
model.
DT
Change in zonally averaged
temperature for July-August.
Increase is greatest at high
latitudes. Reason is ice-albedo
feedback.
Change in northward transport of
latent heat by eddies in midtroposphere in future atmosphere.
Reduced temperature gradient
+
Increased transport of latent heat
Fewer cyclones generated
More persistent pollution events
How do you translate our results into “ozone alert days”?
Model predicts high-pollution days will occur about 66% more frequently in future due to
changes in circulation over Northeast and Midwest.
Best calculation includes full chemistry responding to all the meteorological changes.
Hotter maximum temperatures
Triangles
indicate days of
highest BCt
concentrations.
2050s
2000s
Reduced cloud cover
High maximum temperatures and reduced cloud cover suggest increased
ozone production, amplifying effect of stagnation.
Summary
Model predicts an increase in the severity and duration of pollution
episodes over the Midwest and Northeast U.S. by 2050, even with
constant emissions.
Change in pollution tied to a decrease in the frequency of cold fronts
arriving from Canada, which sweep away the pollution.
2050s
“In an ideal world, scientists would learn in
graduate school how to tell ordinary people
about their world.” Cornelia Dean, NYT
reporter and editor.
2000s