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Investigating Links between Atmospheric Chemistry, Climate, and the Biosphere
Loretta J. Mickley, 4 November 2011
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with Amos Tai, Lee Murray, Xu Yue, Jennifer Logan, Daniel Jacob, Shiliang Wu, Eric Leibensperger, Dominick Spracklen
Wildfires in Quebec, May 31, 2010
Haze over Boston on the same day
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Atmospheric chemistry examines the mix of gases and particles in the atmosphere. Our group mainly focuses on short-lived species: ozone, particles, mercury and their precursors, with lifetimes days to weeks.
Lifetimes in atmospheric chemistry
Centuries: SF6, some CFCs
Decades: most greenhouse gases: CO2, N2O, . . .
9-10 years: CH4 (methane, precursor to ozone and greenhouse gas)
Days-weeks: O3 (ozone), particulate matter (PM)
Seconds: OH, NO
Pollution over Hong Kong
Air pollution over Hong Kong reached dangerous levels one of every eight days in 2009
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Surface ozone and particulate matter are harmful to human health.
EPA’s Technical Support Document for the proposed finding on CO2 as a pollutant.Cites the threat of climate change to air quality
Calculated with standard of 0.075 ppm. Proposed new standards will push more areas into non-attainment.
Number of people living in areas that exceed the national ambient air quality standards (NAAQS) in 2008.
Short-lived species respond to climate change as well as to trends in emissions.
2009
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Surface ozone and particulate matter also affect climate.
Radiative forcing W m-2
ozone
visibleinfra- red
Many particles scatter incoming sunlight (cooling). Ozone absorbs outgoing terrestrial radiation (warming)
particles
IPCC 2007
Yardstick of warming or cooling effect
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O3
O2 hn
O3
Deposition
STRATOSPHERE
TROPOSPHERE
8-18 km
Lifecycle of tropospheric ozone: production is via oxidation of CO, VOCs, and methane in the presence of NOx.
NOx
• Nonmethane volatile organic compounds (VOCs)• NOx = NO + NO2
Human activityFires Biosphere
emissions
Many processes affected by climate
NOxNOx
NOxVOCs
NOx
NOxVOCs
VOCsVOCs
VOCsCO
CO CH4
CH4
Soup of chemical reactionsOzone is produced in the atmosphere in sunlight.
Observations imply importance of biogenic emissions to atmospheric chemistry
Probability of ozone exceedance
Northeast/ mid Atlantic in summer
maximum daily temperature (K)
Pro
babi
lity
Reasons for increasing probability of ozone exceedances at higher max Temps:• Greater stagnation + clear skies• Faster chemical reactions.• Greater biogenic emissions, e.g. isoprene
Lin et al., 2000
1988, hottest on record
Day
sNumber of summer days with ozone exceedances, mean over sites in Northeast
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Life cycle of particulate matter (PM, aerosols)
nucleation coagulation
condensation
wildfirescombustion
soil dustsea salt
. . ... .
cycling
ultra-fine(<0.01 mm)
fine(0.01-1 mm)
cloud(1-100 mm)
combustionvolcanoes
agriculturebiosphere
coarse(1-10 mm) scavenging
precursor gases
Climate change affects many processes, including gas-particle partitioning.
Soup of chemical reactions
NOxNOx
NOx
NOxNOx
VOCs
VOCsVOCs
VOCsVOCs
SO2
NH3
SO2
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Models are useful tools to interpret observations and to investigate past or future atmospheres.
emissionstransportdilutionchemistry
particulate matter (PM)and ozone pollution
population
GEOS-Chem chemical transport model: Global 3-D model describes the transport and chemical evolution of atmospheric pollutants
winds Winds carry pollutants to other boxes.Emissions + chemistry
calculated within box
Meteorology driving GEOS-Chem can come from observations or climate models.
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Meteorology driving 3-D chemical models comes from climate models:
Two ways to run climate models• “nudged” with observations• calculated from first principles
All climate models depend on basic physics to describe motions and thermodynamics of the atmosphere:
E.g., vertical structure is described by hydrostatic equation
( ) ( ) a adPP z P z dz gdz gdz
Climate models also depend on parameterizations for many processes.E.g., microphysics of cloud droplet formation.
Physics + Parameterized processes
Tilt of earth, geography, greenhouse gas content
Weather + Climate
Input Climate model Output
Validation of models involves scrupulously comparing model results to observations.
Since, 1800s, input of reactive nitrogen to ecosystems has increased by more than a factor of 3 globally due to human activity.r = Correlation coefficients NMB = normalized mean biases MNB= mean normalized biases
observations model
Zhang et al., 2011Nitrate wet deposition fluxes, 2006
Biogenic volatile organic compounds (BVOCs): Emissions Parameterization in GEOS-Chem
Base emission for a specified mix of different plant functional types at specified meteorological conditions
INPUTS
MODELBase emissions are scaled for local conditions: vegetation
type, leaf area index, temperature, solar insolation
OUTPUTGridded BVOC emissions
[atoms C cm-2 s-1](includes isoprene and monoterpenes)
Guenther et al., 2006
Big isoprene emitters: Oaks, spruce, firs, sweetgum
Other parameterizations in GEOS-Chem
Soil NOx emissions = f(vegetation type, temperature, precipitation history, canopy reduction, fertilizer usage)
Dry deposition = Resistance in series scheme, with these resistances:Aerodynamic resistance to surfaceBoundary resistance at surface of leafCanopy surface resistance = f(Leaf area index, direct and diffuse sunlight,
gas or particle type)
Wet deposition = f(clouds, rainfall, gas or particle type)
Difficulty is scaling up from small-scale processes to global scale.
How will changing climate affect changing organic carbon particles in the atmosphere?
Fine mass of organic particles, annual mean.
Southeast is a big contributor due to dense vegetation.
Organic particles contribute about 20-40% of particle mass in the US.
What will change in future atmosphere:
air temperature
biogenic emissions
land usevegetationMalm et al., 2004
Effects of Future Biosphere Changes on Air Quality
Plants
Biogenic volatile organic
compound (VOC)
Secondary organic aerosol
(SOA)
[Heald et al. 2008]
Simulated 2000-2100 changes in annual surface SOA concentrations
climate change only climate-driven biogenic emissions change only
anthropogenic land use change only
+ +
Effects of Future Biosphere Changes on Air Quality
[Wu et al. 2011]
Climate- and CO2-driven 2000-2100 changes in areal fractional coverage
Temperate broad-leaved trees Boreal needle-leaved trees
Associated changes in SOA concentrations
20% increase in SOA global burden
Effects of Future Biosphere Changes on Air Quality
Simulated 2000-2150 changes in surface ozone concentrations
Ozone deposition could have consequences for carbon uptake in plants.
climate- and CO2-driven vegetation change only
Plants
Leaf surface Ozone loss
Biogenic VOC
[Wu et al. 2011]
+
++ -
-
Ozone increase or loss (depends
on NOx)
ppb
[Wu et al. 2011]
2000-2100 changes gross primary productivity due to ozone changes
Increasing ozone due to climate change can decrease gross primary productivity.
Sitch et al., 2007
2000 ozone
2100 ozone
GPP GPP
Observed Area burned
Observed Meteorology
Regression Model
Relationship between area burned + meteorology
observationsmodel
How will changing climate affect wildfires and air quality?
Yue et al., 2011
We build a fire prediction scheme that can capture interannual variability in area burned in the Western US.Area burned = f (temperature, rainfall, Palmer drought index, relative humidity, other indices. . .)Each ecosystem has its own relationship between area burned and meteorology.
Ensemble of climate models predict warmer and drier summers in the west.
Temperature Temperature
PrecipitationPrecipitation
Relative Humidity Relative Humidity
DJF JJA
2000-2050 change in meteorological fields, ensemble medians in each gridbox.
A1B scenario – moderate increases in greenhouse gases.
Yue et al., 2011
Meteorology from 15 climate
models
Regression Model
Calculated area burned for present-day
and future
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We calculate changes in area burned for 2000-2050, using an ensemble of IPCC model results.Area burned increases 20-120% across Western US, but models show range of uncertainty.
Spracklen et al., 2009Yue et al., 2011
2000-2050 changes in meteorology from 15 IPCC AR4 climate models.
different ecosystems in Western US
The total area burned is predicted to increase by 60~120% over western US by the midcentury
Years
1986 1990 1995 2000 2051 2055 2060 2065
Present-day observations
Ensemble median values of predictions
Spread of predictions
1990 2000 2055 2065
Change in area burned is especially large in Southwest US, where area burned doubles.
105 ha
105 haYue et al., 2011
The length of fire season increases by 3 weeks in 2050s relative to present day.
163 days 185 days
End day
Start day
Calculations with observations
Ensemble median values of predictions
Spread of predictions
Yue et al., 2011
Can we also simulate the effects of insect outbreaks on forests in a global chemistry model?
Arneth and Niinemets, 2010
Both fires and insect outbreaks are influenced by climate. Can we build a probabilistic model of insect outbreaks by ecosystem?
Investigations of the oxidation capacity of the atmosphere during the Last Glacial Maximum
Ongoing project to look at how changing land cover and climate affect oxidation capacity of atmosphere.Biogenic species could play a role: decreased concentrations could increase OH levels.
Murray et al., in progress
Emissions of biogenic species
Annual mean emissions of isoprene
Present-day
Preindustrial
CLIMAP LGM
Webb LGM
Comparison to observed sulfate concentrations shows good agreement.
Sequence shows increasing sulfate from 1950-1980, followed by a decline in recent years. Most of aerosol has already cleared by 2010.
1950 1960
1970 1980
1990 2001
Leibensperger et al., 2011
Calculated trend in surface sulfate concentrations, 1950- 2001.
Trend in aerosols over United States suggests cleaner skies, possible warming.
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Each scenario includes an ensemble of 3 simulations.
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GISS GCM A1B greenhouse gases constant aerosols
A1B greenhouse gases zero US aerosols
1950 1975 2000 2025 2050
We test the effect of changing U.S. aerosols on regional climate.
Mickley et al., 2011
Two scenarios.
Removal of anthropogenic aerosols over US increases annual mean surface temperatures by 0.5 o C. Summertime temperatures increase as much as 2 oC during heatwaves.
Mean 2010-2050 temperature difference: No-US-aerosol case – ControlWhite areas signify no significant difference.Results from an ensemble of 3 for each case.
Warming due to 2010-2050 trend in greenhouse gases.
Additional warming due to zeroing of US aerosols
Mickley et al., 201127
Calculation of maximum temperatures in climate models is sensitive to choice of parameters having to do with land cover/soil.
Lower and upper estimates of JJA maximum temperatures in 2x CO2 atmosphere
Central 80% range of increases for 44 versions of one climate model
oC
Percent variability in Tmax accounted for by vegetation parameters.
Clark et al., 2010 28
Forest roughness parameter Vegetation root depth
Lower estimate Upper estimate
50%30%6%
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Effect of kudzu invasion on surface air quality
Hickman et al., 2010
By fixing atmospheric nitrogen at a rapid rate, kudzu invasion leads to significant release of nitric oxide, an ozone precursor.
Mean July emissions at 3 sites in Georgia
kudzu native
NO
N2O
Calculated change in the number of ozone exceedance days in summer due to a 28% increase in soil NOx emissions accompanying large kudzu invasion.
days
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Collaborations with ecologists:• Enhance knowledge of interactions between biosphere and atmosphere, and
how to model those interactions• Improve understanding of response of ecosystems to climate change
Specific processes that will change with changing climate or changing emissionsbiogenic emissions, including methane, VOCsdeposition of nitrogen, ozone, and other speciessoil NOx emissionsinsect-driven outbreaks and their consequences