The Climate Change

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The Climate Change Urban Pollution Relationship

• Effects of climate change on air quality
• Effects of aerosols on regional climate

Smog over Pittsburgh, ranked 1 city for
particulate pollution in 2008 by ALA
Loretta J. Mickley, Harvard University also
Shiliang Wu, Jennifer Logan, Dominick Spracklen,
Amos Tai, Rynda Hudman, Daniel Jacob, Moeko
Yoshitomi, Eric Leibensperger, Havala Pye
Funding for this work NASA, EPA, EPRI
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Millions of people already live in areas of high
pollution.
Number of people living in areas that exceed the
national ambient air quality standards (NAAQS) in
2006.
0.08 ppm
Calculated with old 0.08 ppm standard. New
standard of 0.075 ppm will push more areas into
non-attainment.
65 mg/m3
EPAs Technical Support Document for the proposed
finding on CO2 as a pollutant. Cites the threat
of climate change to air quality.
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O2
hn
Chemistry of tropospheric ozone oxidation of CO,
VOCs, and methane in the presence of NOx
O3
STRATOSPHERE
8-18 km
TROPOSPHERE
Stagnation promotes ozone production
hn
NO2
NO
O3
hn, H2O
OH
HO2
H2O2
Deposition
CO, VOC
Nitrogen oxide radicals NOx NO NO2
combustion, soil, lightning Methane wetlands,
livestock, natural gas Nonmethane volatile
organic compounds (VOCs) vegetation,
combustion, industry CO (carbon monoxide)
combustion, VOC oxidation
Tropospheric ozone precursors
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Weather plays a large role in ozone air quality.
The total derivative dO3/dT is the sum of
partial derivatives (dO3/dxi)(dxi/dT). x
ensemble of ozone forcing variables that are
temperature-related.
Lin et al., 2001
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Cyclones crossing southern Canada affect ozone
air quality in Eastern US.
cold front
EPA ozone levels
L

• Stalled high pressure system associated with
• increased biogenic emissions
• clear skies
• weak winds
• high temperatures.

3 days later
cold front
L
Cold front pushes smog poleward and aloft on a
warm conveyor belt.
Hazardous levels of ozone
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Decline in mid-latitude cyclone number over
mid-latitudes leads to more persistent stagnation
episodes, more ozone.
1950-2006 trend in JJA cyclones in S. Canada
Trend in cyclones appears due in part to weakened
meridional temperature gradients, reduction of
baroclinicity over midlatitudes.
1980-2006 trends
Trend in emissions and trend in cyclones have
competing effects on surface ozone. If cyclone
frequency had remained constant, we calculate
zero episodes over Northeast.
Mickley et al., 2004 Leibensperger et al., 2008
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Particulate matter (PM, aerosols) sources and
processes
ultra-fine (lt0.01 mm)
fine (0.01-1 mm)
cloud (1-100 mm)
precursor gases
oxidation
nucleation
cycling
coagulation
H2SO4
SO2
condensation
RCO
VOCs
coarse (1-10 mm)
scavenging
NOx
HNO3
wildfires
NH3
carbonaceous combustion particles
combustion biosphere volcanoes
soil dust sea salt
agriculture biosphere
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• Observed correlations of total PM2.5 with
  meteorology
• Precipitation
• Stagnation
• Temperature
• Positive correlation with temperature occurs due
  to
• Increased oxidation of SO2
• Greater biogenic emissions

Precipitation
Stagnation
Results from EPA AQS database 1000 sites
sampled every 1-6 days from 1998 to 2007.
Observed correlations provide means to test
model simulations. E.g., observed sulfate
response to temperature is 0.08 µg m-3/K, 4x
greater than Dawson et al. 2007 model.
Temperature
Tai et al., ms.
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What do models project for future air quality? We
have developed GCAP (Global Change and Air
Pollution).
GISS GCM Physics of the atmosphere Qflux ocean or
specified SSTs
GEOS-Chem Emissions Chemical scheme Deposition
met fields
met fields
chemistry fields
met fields
Regional chemistry model
Regional climate model
Chemistry model driven by GCM meteorology to
study influence of climate on air quality.
Mickley et al., 2004
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2000-2050 climate change increases JJA surface
ozone 1-5 ppb on average across US, 5-10 ppb
during heat waves in Midwest
Max. 8-hr-avg ozone
Effect of climate change alone
2000s conditions 2050s climate 2050s
emissions 2050s climate emis
Increase of summer max-8h-avg ozone
99th percentile
Cumulative probability ()
Midwest
Daily max 8h-avg ozone averaged in JJA (ppb)
We define the climate change penalty as the
effort required to meet air quality standards
under future climate change.
Wu et al., 2007
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Change in annual mean surface inorganic aerosol
from 2000-2050 climate change (no change in
emissions)
Increase in Northeast due to increased
temperature and accelerated oxidation rates
Decrease in Southeast due mainly to increased
precipitation.
Calculation of future aerosol levels is
challenging because of uncertainty in future
rainfall over mid-latitudes. Also, mix of aerosol
species is expected to change, so sensitivity to
climate will also change.
Present-day annual average
Pye et al., 2009
sulfate nitrate ammonium
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Projected increase in wildfires could affect air
quality in the US.
We predict future wildfires using observed
relationships between meteorology and area burned
for different ecosystems.
2000-2050 changes in fire season surface ozone.
Spracklen et al., 2009 Hudman et al, ms.
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Present-day radiative forcing due to aerosols
over the eastern US is comparable in magnitude,
but opposite in sign, to global forcing due to
CO2.
Globally averaged radiative forcing due to CO2 is
1.7 Wm-2. warming
Over the eastern US, radiative forcing due to
sulfate aerosols is -2 Wm-2.
cooling
IPCC, 2007 Liao et al. , 2004
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Is the climate response to changing aerosols
collocated with regions of radiative forcing?
Recent US Climate Change report says NO Trends
in short-lived species (such as aerosols) affect
global, but not regional, climate. Regional
emissions control strategies for short-lived
pollutants will . . . have global impacts on
climate. U.S. Climate Change Science Program,
Synthesis and Assessment Product 3.2
Harvards work to date says YES Removal of the
aerosol burden over the eastern US will lead to
regional warming, in a way that the US Climate
Change report would not have recognized.
Calculated present-day aerosol optical depths
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What is the influence of changing aerosol on
regional climate? In pilot study, we zero out
aerosol optical depths over US.
GISS GCM
For pilot study, 2 scenarios were simulated
Control aerosol optical depths fixed at 1990s
levels. Sensitivity U.S. aerosol optical
depths set to zero (providing a radiative forcing
of about 2 W m-2 locally over the US)
elsewhere, same as in control simulation. Each
scenario includes an ensemble of 3 simulations.
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Removal of anthropogenic aerosols over US leads
to a 0.5-1o C warming in annual mean surface
temperature.
Additional warming due to zeroing of aerosols
over the US.
Warming due to 2010-2025 trend in greenhouse
gases.
Mean 2010-2025 temperature difference
No-US-aerosol case Control White areas signify
no significant difference. Results from an
ensemble of 3 for each case.
Annual mean surface temperature change in
Control.
Mickley et al., ms.
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The regional surface temperature response to
aerosol removal appears to persist for many
decades in the model.
Annual mean temperature trends over Eastern US
Temperature response is initially strongest in
winter. Summertime temperature response kicks in
around 2030.
Mickley et al., ms
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• Implications for policymakers
• Policymakers need to consider climate change
  penalty, i.e., the additional emission controls
  necessary to meet a given air quality target.
• Efforts to clear the air of anthropogenic
  aerosol over the US may exacerbate regional
  warming.

Directions for future research Understand causes
in interannual variability of air
quality. Investigate model sensitivity of
pollutants to meteorology, and compare to
observations. Understand chemistry of biogenic
species, e.g. isoprene Improve emission
inventories for recent past/future, especially
for NH3, black carbon, organic carbon,
mercury Improve global and regional models of
mercury Understand secondary organic aerosols
sources, chemistry. For cities improve modeling
of fine scale features, investigate how best to
downscale meteorology from global climate models,
test effects of land use change. Understand
aerosol-cloud interactions, characterize aerosol
composition
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Extra slides
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Ozone exceedances in eastern US correlate with
frequency of cyclone passage through southern
Canada/Great Lakes region.
Correlation between cyclone number in red and
green boxes and US ozone exceedances over 27-year
record, JJA
Storm tracks for 3 years (NCEP, summer 1979-1981)
Storm tracks calculated with cyclone tracker
tool, applies cyclone criteria to observations or
model output.
Leibensperger et al., 2008
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Projected increase in wildfires could affect air
quality in the US.
2000-2050 change in JJA surface organic aerosol
due to increased wildfires
We have developed a fire prediction tool based on
observed relationships between meteorology and
area burned. Applying these relationships to GCM
meteorology, we predict area burned and future
emissions of wildfire pollutants.
mg m-3
Changes in JJA surface ozone concentrations
Spracklen et al., 2009 Hudman et al, ms.
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We define the climate change penalty as the
effort required to meet air quality goals in the
future atmosphere.
40 cut in NOx 2050s climate
present-day NOx emissions climate

climate change penalty
40 cut in NOx present-day climate
50 cut in NOx 2050s climate
20002050 climate change implies an additional
25 effort in NOx emission controls to achieve
the same ozone air quality.
Midwest surface ozone
Wu et al., 2007