loretta j. mickley, harvard university
DESCRIPTION
Projected trends in global temperature. Effects of Climate Change on U.S. Air Quality. Loretta J. Mickley, Harvard University Shiliang Wu, Eric Liebensperger, Moeko Yoshitomi, Dominick Spracklen, Brendan Field Daniel Jacob, David Rind, Cynthia Lin, David Streets. - PowerPoint PPT PresentationTRANSCRIPT
Loretta J. Mickley, Harvard University
Shiliang Wu, Eric Liebensperger, Moeko Yoshitomi, Dominick Spracklen, Brendan Field
Daniel Jacob, David Rind, Cynthia Lin, David Streets
Effects of Climate Change on U.S. Air Quality
Projected trends in global temperature
Probabilityof ozone exceedancevs. daily max. temperature
Day-to-day weather plays a large role in surface air quality (1).
Northeast
Ozone is strongly correlated with temperature in observations; this is due to (1) chemistry, (2) biogenic VOC emissions, (3) joint association with stagnation.
1988, hottest on record
Ave
rage
num
. of
day
s
Number of summer days with ozone exceedances (> 84ppb) over northeast U.S.
Lin et al., 2001
1992, coldest on record, due to Pinatubo eruption
Day-to-day weather plays a large role in surface air quality (2).
Stalled high pressure system increases ozone due to:
• increased biogenic emissions
• clear skies
• weak winds
• high temperatures.
cold frontEPA ozone levels
3 days later
Cold front pushes smog poleward and aloft on a warm conveyor belt.
cold front
L
L85-104 ppb 105-124 ppb
cyclone
Nitrogen oxide radicals; NOx = NO + NO2
combustion, soils, lightningMethanewetlands, livestock, natural gasNonmethane volatile organic compounds (NMVOCs)vegetation, combustion, industryCO (carbon monoxide)combustion, VOC oxidation
O3
O2h
O3
OH HO2
h, H2O
Deposition
NO
H2O2
CO, VOC
NO2
h
STRATOSPHERE
TROPOSPHERE
8-18 km
Troposphericozone
precursors
generally limiting
Chemistry of tropospheric ozone
What processes will climate change affect?
transport
A decrease in cyclone frequency across mid-latitudes has been
observed (and calculated) for recent decades.
Observed trend in winter cyclone frequency over Northern Hemisphere.
McCabe et al., 2001
Calculated trend in summer cyclone frequency, from GISS 2x2.5 GCM, 23 layers
Climate models tend to predict decrease in mid-latitude cyclogenesis in future due to:• decrease in meridional temperature gradient • more efficient poleward transport of latent heat
Leibensperger et al., 2007
Ozone exceedances over eastern United States anti-correlate with cyclone frequency over Southern Canada/ Great Lakes region.
Correlation of 1980-2006 summertime ozone exceedances with cyclone number in the red and green boxes for each summer.
weak correlation
Stronganti-correlation
sample summertime storm tracks, 1979-81
NCEP/NCAR reanalysis
Cyclone trend works against improvements in emissions.
Number of summertime ozone exceedance days in Northeast dropped from 38 in 1980 to ~8 in 2006, but would have dropped to 0 in absence of cyclone trend.
Leibensperger et al., in prep.
Observed 1980-2006 trend in summertime cyclone number, 40-50 N
Number of O3 exceedances in Northeast
Interannual variability of cyclone frequency and ozone exceedance is highly anticorrelated (r = - 0.64).
Cyclone trend from NCEP/NCAR reanalysis would imply large effect on ozone trends.
Global change and air pollution (GCAP):Five models working together to provide information on climate
change impacts
Model for precursor emissions
archive met fields
GEOS-CHEM
Global chemistry model
CMAQ
Regional chemistry model
MM5 Mesoscale
model
archive chemistry
archive met fields
1950 2000 2025 2050 2075 2100
GISS general circulation model
Spin-up
changing greenhouse gases
Pollution episodes double in duration in 2050s due to decreasing frequency of cyclones ventilating the eastern U.S.
2045-2052
1995-2002
July - AugustGISS GCM simulations for 2050s vs. present-day climate. CO tracer: constant, present-day anthropogenic emissions+ sink of present-day OH fields.
Fewer cold front passages allow pollutants to build up.
Changes at high end of distribution due to 10-20% decrease in summertime cyclogenesis.
Mickley et al., 2004
• Models agree that 2000-2050 climate change will decrease background ozone but increase surface ozone. We find an increase of 3-5 ppb over large regions.
• Most but not all models find maximum effect during pollution episodes (up to 10 ppb in ours) due to increased stagnation and higher temperatures.
• Most models find significant effects in Northeast/ Midwest.
• Many models disagree in Southeast partly due to different mechanisms for oxidation of biogenic isoprene (the dominant VOC precursor)
Wu et al., 2008
ppb
Increased water vapor sink
Higher temperatures, stagnation
2000-2050 A1 climate change increases summertime ozone.
Changes in summer 8-h avg. daily maximum ozone from 2000-2050 climate change
Effect of 2000-2050 climate change on pollution episodes.
Wu et al., 2008
Increased maximum temperatures during heat waves leads to increased ozone.
Amplification of temperatures at extreme due to • soil moisture feedbacks • 17% decreased cyclone frequency.
Cumulative probability (%)
Max
. 8-
hr-
avg
ozo
ne 2050s climate
99th percentile
Midwest
Dai
ly m
axim
um t
empe
ratu
re (
K)
Cumulative probability (%)
2050s
2000s
Maximum JJA temperatures Maximum JJA 8-h avg ozone
40% decrease in NOx2050s climate + NOx
2000s climate
-1 -.5 0 .5 1correlationcoefficient R
GCAP modelpresent-day climate (3 years)
Correlations of daily max-8h-avg ozone with daily max temperature in Jun-Aug
Observations (1980-1998)
Yoshitomi et al., in progress
We can use ozone-temperature correlations as a test of model sensitivity to climate change, esp in Southeast US
Regions of strongest correlation in model and observations.
Most of the variability in wildfire frequency is due to year-to-year changes in surface temperatures and precipitation.
Forest fires in western US have big impact on particle concentrations and on surface ozone.
Area burned and temperature in Canada over the last century
Gillet et al., 2004
EPA wildfire project: How will changing forest fire frequency affect future air quality over the United States?
What will happen next? Dominick Spracklen has developed a fire prediction tool to calculate future area burned using GISS GCM meteorological variables. . . . 2050 and beyond
Results show far: Future 2040-2050 biomass consumption by wildfires over the western United States is ~50% greater than for present-day.
Plot shows standardized departures from the 1996-2055 mean.
Annual total biomass consumed by forest fires, 1996-2055
Spracklen et al., in progress.
Rynda Hudman at Harvard is investigating effect of future forest fires on surface ozone concentrations.
Increased 2050s wildfire activity leads to 3-6 ppb increase in afternoon mean ozone in July over western U.S.
2051
[ppbv]
Biomass burning NOx emissions
2000
[Gg NO]
Mean of 5 ppbv enhancement due to fires a > 2 SD
Hudman et al., in progress
JJA surface ozone
ConclusionsIn the 1980-2006 NCEP/NCAR record, we find a decline in cyclone frequency
of -0.15 cyclones/y, which may have limited the efficacy of air pollution regulations.
For 2050-2000 A1B climate change, we calculate a10-20% decline in cyclone frequency, lengthening pollution episodes over Midwest and Northeast.
Climate change is expected to degrade U.S. ozone air quality. The summer average daily max-8h ozone increases by 2-5 ppb over large areas due to 2000-2050 climate change with the IPCC A1B scenario. Largest effect is during pollution episodes, when ozone increases by as much as 10 ppb.
Summertime ozone concentrations are predicted to increase by 3-6 ppb over parts of western US due to increasing wildfire frequency in the 2050s.
Projected trends in global NOx emissions for a range of scenarios.
Extra slides
Why is ozone in the Southeast insensitive to climate change?
Isoprene has competing effects on ozone
Sensitivity test: Isoprene emissions +30% Δ(O3)
2000 2050 / 2000
Isoprene emissions
RO2 + NORONO2 (sink for NOx)
Isoprene + OH RO2 (OH sink)
Isoprene + O3 M (O3 sink)O3
RO + NO2 (O3 formation) O3
Wu et al., 2008