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• ATMOSPHERIC CHEMISTRY and AEROSOLS
Peter Hess Cornell University
• WHOLE ATMOSPHERE COMMUNITY CLIMATE MODEL
Michael Mills NCAR
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Chemical Effluents to the Atmosphere
Where does it go? What are the impacts? What are the processes to be modeled?
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Where do Pollutants Go?
-‐Chemically transformed -‐Deposited onto surface through contact (dry deposi;on) -‐Dissolved in rain and deposited onto surface (wet deposi;on)
How are these processes simulated in a CESM ?
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Atmospheric Chemistry and Aerosols
Earth System
• Paths to sustainability often involve chemically active species - Biofuels: CO2 , N2O
• Climate – Health – Air Pollution Interactions - Emission Tradeoffs
- Climate – Biosphere - Hydrological Cycle-
Wetland Emissions (CH4) Soil Emissions (NO, N2O) Biogenic Emissions
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RF (w/m2) GWP CO2: 1.66 1.0 Ozone: 0.35 Methane: 0.48 25 N2O: 0.16 298 CFCs: 0.34 100 - >10000
Radiative Impacts (1)
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Smoke from forest fires burning in Alaska and the Yukon, travelling into the
Arctic over ice-covered areas
Partly absorbing dust aerosol downwind of Sahara
Absorbing aerosols (black carbon, dust) warm the climate by absorbing solar Radiation, other aerosols (sulfate) cool the climate by reflecting solar radiation
AEROSOLS
NET FORCING: -0.5 W/m2
Radiative Impacts (2)
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Indirect Effect
Ramanthan et al., Science, 2001
Radiative Impacts (3)
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N ~ 100 cm-3
W ~ 0.75 g m-3
re ~ 10.5 µm
N ~ 40 cm-3
W ~ 0.30 g m-3
re ~ 11.2 µm
from D. Rosenfeld
Indirect Effects: -Clouds Brighter -Precipitation Suppressed: More Persistent Clouds
NET FORCING: -0.7 W/m2
Radiative Impacts (4)
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AVHRR, 27. Sept. 1987, 22:45 GMT US-west coast
NASA, 2002 Atlantic, France, Spain
SATELLITE IMAGES OF SHIP TRACKS Radiative Impacts (5)
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Direct radiaFve forcing: ozone and methane, aerosols Aerosol indirect effects
Radiative Impacts (6)
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Chemistry to climate Radiative Impacts (7)
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Ozone
-Detrimental for plants and crops- • Approximately a 20-30% reduction of winter wheat in the Yangtze
Delta region due to ozone exposure (Huixang et al)
Biogeochemical Impacts (1)
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Ozone and vegetaFon
Sitch et al., 2007
Radiative impact of ozone on CO2 cycle may exceed its direct radiative impact (-0.35 W/m^2)
Biogeochemical Impacts (2)
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Nitrogen DeposiFon and Response of Carbon
-Quinn Thomas, Nature Geoscience
Data from 20,067 plots remeasured during the early 1980s to mid-1990s by the US Forest Service Forest Inventory and Analysis (FIA) Program
Biogeochemical Impacts (3)
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Diffuse FracFon of RadiaFon
Mercado et al., 2009
Biogeochemical Impacts (3)
Simulated percentage change (colour scale) in diffuse fraction between 1950 and 1980
Diffuse fraction contribution to land carbon accumulation between 1950 and 1980 (grams C/m^2-year)
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∂µ/ ∂t = - · V µ +T + Ω µ + S(x,y,z,t) + L
Explicit Transport
Chemistry Emissions Physical Losses
µ: vector of constituents, typically ~100 V: velocity field Ω: reaction matrix: reaction coefficients, photolysis rates, species concentrations S: emissions L: physical losses: dry and wet deposition
Param. Transport
Model Specification
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Emissions Natural Anthropogenic
Lightning (NO) Wetlands (CH4) Trees (VOCs) Soils (NO)
Combustion (NO, CO) --Cars, Factories
-Biomass Burning -Agriculture - NH3, CH4, N2O, -Landuse Change
Emission Specification:
-User-specified netcdf files -No explicit response to climate change • Namelist Control Parameter
-Lightning, calculated internally • Strength Namelist Control Parameter
OR
Emissions Chemistry Physical Losses
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InteracFve Emissions Atmosphere
Emissions
Atmospheric Feedback -Temperature -Precipitation -Chemical Deposition
Interactive Emissions in Model Lightning, Biogenic VOC, Biomass burning, Soil NO (partially)
Interactive Emissions in Development Methane, Full Suite of Odd Nitrogen
Future Human component?
Emissions Chemistry Physical Losses
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• Chemistry consists of highly coupled stiff differential equations
d[NO2]/dt = k1[NO][O3] + k2[NO][HO2] –j[NO2] –k4[NO2][OH]+… d[HO2]/dt = k5[CO][OH] – k2[NO][HO2] –k6[HO2][O3] + …
-> increases cost by ~ 5x for reasonably complex mechanisms
• Vastly different time-scales [O(sec) – O(years)] occur in chemical equations
• Coupled equations solved w/ implicit and explicit solvers
• Chemical mechanism (i.e., the selected chemistry) is a parameterization of the full chemistry
• Selection depends on the problem addressed
Emissions Chemistry Physical Losses
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rate uncertain to ~10x
yield uncertain by ~2
yield not known
Deposition not known
Deposition not known
Thousands of Atmospheric Reactions: Isoprene ~50,000
Emissions Chemistry Physical Losses
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Select Chemical Mechanism (problem dependent)
i) Predefined mechanism in build configura;on -chem trop_mozart | trop_ghg | trop_bam | trop_mam3 |
trop_mam7 | waccm_mozart | waccm_ghg | super_fast_llnl | none
ii) User-‐specified mechanism defined in build -usr_mech_infile $mechanism_file
Allow user to specify a customized preprocessor input file
Determines the number of advected tracers
Emissions Chemistry Physical Losses
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mechanism file:
SPECIES
Solution CO End Solution
Fixed OH End Fixed
END SPECIES
CHEMISTRY
Reactions [usr8] CO + OH -> CO2 + HO2 End Reactions
Ext Forcing CO<-dataset End Ext Forcing
END CHEMISTRY
Example of preprocessor input file
Emissions Chemistry Deposition
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Preprocessor input file Chemistry code
Preprocessor
Build
CAM-‐chem
Preprocessor Emissions Chemistry Physical Losses
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DeposiFon processes • Dry deposiFon: uptake of chemical consFtuents by plants and soil (handled by CLM), water
-‐Depends: species solubility, reacFvity, surface characterisFcs, meteorology
-‐Impacted species: Namelist control parameter
• Wet deposiFon: uptake of chemical consFtuents in rain or ice (linked to precipitaFon, both large-‐scale and convecFve)
-‐ Depends: species solubility
-‐Impacted species: Namelist control parameter
Emissions Chemistry Physical Losses
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AEROSOLS
Aerosol Microphysics Precursor Emissions
Primary Emissions
Deposition (wet, dry)
Aerosols (1)
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26
Bulk Aerosol Model (BAM)
• External mixtures of all important aerosol types: sulfate, sea salt, dust, hydrophobic and hydrophilic OC & BC
• PredicFon of aerosol mass • Number proporFonal to mass
Prescribed size distribuFon • Aerosol aging set diagnosFcally (through a Fmescale)
• Coupled to 2-‐moment cloud microphysics • Tuned to produce an acceptable climate
Aerosols (2)
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Benchmark 7-Mode Modal Aerosol Model (MAM) Simplied 3-Mode Scheme also implemented
27
Aitken number sulfate ammmonium secondary OM sea salt
Accumulation number sulfate ammonium secondary OM hydrophobic OM BC sea salt
Primary Carbon number hydrophobic OM BC
Fine Soil Dust number soil dust sulfate ammonium
Fine Sea Salt number sea salt sulfate ammonium
Coarse Soil Dust number soil dust sulfate ammonium
Coarse Sea Salt number sea salt sulfate ammonium
coagulation condensation
All modes log-normal with prescribed width.
Total transported aerosol tracers: 31
Cloud-borne aerosol and aerosol water predicted but not transported.
7-mode: Computer time is ~100% higher than BAM 3-mode: Computer time is ~30% higher than BAM
Aerosols (3)
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Changes w/ Modal Formulation • Prediction of Number and Mass • Consistent coupling with Morrison-Gettlemen
microphysics • Consistent simulation of the indirect effect (-‐1.0 to -‐1.8
W/m2) • Aging of primary carbon to accumulation mode based on
sulfate coating from condensation & coagulation • Radiation based on mixed phase aerosols (from Ghan and
Zaverhi, 2007) • Coagulation within, between modes • Dynamic condensation of trace gas (H2SO4, NH3) on
aerosols • New particle formation (in UT and BL) • Ultrafine sea salt emissions from Martensson et al. • A new secondary organic aerosol treatment: reversible
condensation of SOA (gas)
Aerosols (4)
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Example of build configuraFon Predefined chemistry packages:
-chem trop_mozart | trop_ghg | trop_bam | trop_mam3 | trop_mam7 | waccm_mozart | waccm_ghg | super_fast_llnl | none
Predefined bulk aerosol/GHG packages:
-prog_species SO4 | DST | SSLT | OC | BC | GHG | CARBON16
Configure will generate a preprocessor input file for any combination of these predefined prognostic aerosol and GHG packages.
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Temperature Ozone Exceedances
Netherlands: 1000-‐1400 deaths, 400–600 air polluFon-‐related deaths (Fischer et al.) Driven by: stagnation, biogenic hydrocarbon emissions, forest fires, chemistry
Examples: Chemistry-Climate Interactions (1)
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Examples: Chemistry-Climate Interactions (2)
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NO NO2 hν
O3 (Ozone)
Hydrocarbon OxidaFon
OH HO2 h ν, H2O
CO, CH4
CO2, H2O
<.1 pptv 1.8 ppm
Examples: Chemistry-Climate Interactions (3)
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2030: GHG Increase + MFR Aerosols 2030: GHG Increase Only
Kloster et al., 2009
Examples: Chemistry-Climate Interactions (4)
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Examples: Chemistry-Climate Interactions (4)
Climate amplifier due CH4 emissions from wetlands
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Change in Soil Temperature, 2050, GFDL
-permafrost melting, permafrost pool ~1/3 global soil carbon -additional emission of 1-4 PC/year over 100 years if ½ permafrost thaws -release of CO2 or CH4 -CH4 favored in wet conditions
Examples: Chemistry-Climate Interactions (5)
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‘World is running out of nitrogen…’ Sir William Crooks, president of the British Association for the Advancement of Science
BNF
Haber-Bosch
Slide courtesy Marina Molodvskaya
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Namelist control parameters
• Photolysis rates: LUT or inline • Surface emissions/Other sources
• Species affected by dry deposiFon • Species affected by wet deposiFon • Lightning strength • Lower boundary condiFons • Stratosphere overwriFng
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Possibility of using observed meteorology (campaign)
• Goal: use meteorological fields as close as possible to observed condiFons
• Method
1) CAM: processing of meteorological fields through dynamical core
2) WACCM: relaxaFon
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Chemistry in CAM
• Must be done in FV dynamical core (tracer conservaFon)
• Requires to build CAM with specific opFon
• Requires use of pre-‐defined chemistry or user-‐specified