atmospheric chemistry and aerosols

•  ATMOSPHERIC CHEMISTRY and AEROSOLS

Peter Hess Cornell University

•  WHOLE ATMOSPHERE COMMUNITY CLIMATE MODEL

Michael Mills NCAR

Chemical Effluents to the Atmosphere

Where does it go? What are the impacts? What are the processes to be modeled?

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 ?

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

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)

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


Indirect Effect

Ramanthan et al., Science, 2001


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


AVHRR, 27. Sept. 1987, 22:45 GMT US-west coast

NASA, 2002 Atlantic, France, Spain

SATELLITE IMAGES OF SHIP TRACKS Radiative Impacts (5)

  Direct radiaFve forcing: ozone and methane, aerosols   Aerosol indirect effects


Chemistry to climate Radiative Impacts (7)

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)

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)


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


Diffuse FracFon of RadiaFon

Mercado et al., 2009


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)

∂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

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

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?


• 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


rate uncertain to ~10x

yield uncertain by ~2

yield not known

Deposition not known

Deposition not known

Thousands of Atmospheric Reactions: Isoprene ~50,000


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


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

Preprocessor input file Chemistry code

Preprocessor

Build

CAM-‐chem

Preprocessor Emissions Chemistry Physical Losses

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


AEROSOLS

Aerosol Microphysics Precursor Emissions

Primary Emissions

Deposition (wet, dry)

Aerosols (1)

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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)

Benchmark 7-Mode Modal Aerosol Model (MAM) Simplied 3-Mode Scheme also implemented

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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)

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)

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)

NO NO2 hν

O3 (Ozone)

Hydrocarbon OxidaFon

OH HO2 h ν, H2O

CO, CH4

CO2, H2O

<.1 pptv 1.8 ppm


2030: GHG Increase + MFR Aerosols 2030: GHG Increase Only

Kloster et al., 2009



Climate amplifier due CH4 emissions from wetlands

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


‘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

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

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

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

atmospheric chemistry and aerosols

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