WRFChem

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WRF/Chem

• Air chemistry basics
• Description of chemistry within WRF/Chem

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Tropospheric ozone
In the troposphere the abundancy of ozone depends
on the NOx
NO2 h? ? NO O (? lt 424 nm) O O2 ?
O3 NO O3 ? NO2 O2
There is no ozone production
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Tropospheric ozone
NO2 h? O2 O O3 NO HO2 NO RO2 NO
NO O O3 NO2 O2 NO2 OH NO2 RO
The presence of peroxy radicals cause a
perturbation of the NOx y O3 cycle
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Tropospheric ozone
The hydroxyl radical OH

• It is produced by the O3 photolysis
• O3 h? ? O(1D) O2 (? lt 320 nm)
• O(1D) M ? O M (O2 ? O3) (90)
• O(1D) H2O ? 2 OH (10)

• OH initiates the oxidation of an ample range of
  atmospheric compounds.
• It is also refered to as the atmospheric
  detergent.
• It is very reactive and its recycling is very
  efficient.

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Tropospheric ozone
CO oxidation
CO OH ? CO2 H H O2 M ? HO2 M NO
HO2 ? NO2 OH NO2 h? ? NO O O O2 M ?
O3
CO 2 O2 h? ? CO2 O3
O3 production
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Tropospheric ozone

• Cycle termination
• OH NO2 ? HNO3
• HO2 HO2 ? H2O2
• HNO3 and H2O2 can photolyze or react with OH
  (reversible reaction)
• - slow reactions
• - soluble in water
• - sink in the PBL

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Tropospheric ozone
CH4 oxidation
CH4 OH ? CH3 H2O CH3 O2 M ? CH3O2
M CH3O2 NO ? CH3O NO2 CH3O O2 ? HCHO
HO2 HO2 NO ? OH NO2 2NO2 h? (O2) ? NO
O3
CH4 4 O2 2 h? ? HCHO 2O3 H2O
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Tropospheric ozone
HCHO Oxidation

• HCHO h? ? H2 CO
• ? H HCO
• HCHO OH ? HCO H2O

HCO O2 ? HO2 CO H O2 ? HO2 HO2 NO ?
OH NO2
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Tropospheric ozone
Cycle termination OH NO2 ? HNO3 HO2 HO2
? H2O2 also HO2 CH3O2 ? CH3OOH O2 Methyl
hydroperoxide (CH3OOH) can photolyze or react
with OH resulting in a lifetime of 2 days and
return radicals to the system.
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Tropospheric ozone
VOC oxidation
RH OH ( O2) ? RO2 H2O RO2 NO ? RO
NO2 RO O2 ? RCHO HO2 RCHO OH ?
RC(O)O2 H2O RC(O)O2 NO ? NO2 RO2 CO2
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Tropospheric ozone

• Simplification
• O3 photolysis is most significant source of OH.
• Oxidation of hydrocarbons by OH
• - Production of peroxyls (RO2, HO2) which lead
  to a
• perturbation of the O3/NOx cycle.
• - Production of carbonyl compounds (aldehydes,
• ketones) which follow the oxidation chain.
• - OH recycling.
• Cycle termination by nitric acid (HNO3)
  formation
• (OH NO2 ? HNO3) o peróxidos (H2O2, ROOH)

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What is RH?
VOC category Species
Alkanes
CH4 Methane CH3-CH3 Ethane CH3-CH2-CH3 Propane
and hundreds more .
Alkenes
CH2CH2 Ethene CH3-CHCH2 Propene CH3-CH2-CHCH
2 1-Butene CH3-CHCH-CH3 2-Butene
Alkynes
HCCH Acetylene
Aromatics
Ring structured alkenes
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Problem
There are hundreds of VOCs emitted to the
atmosphere which are then involved in thousands
of reactions. It is impossible to represent all
of these species and reactions explicitly in a
three-dimensional Eulerian model. Therefore, they
have to be lumped into manageable set of VOC
classes . Lumping structure based molecule
based
Inorganic chemistry is less complex and can be
treated reasonably explicitly
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A generalized chemical mechanism
NO2 h? ? NO O O O2 ? O3 NO O3 ? NO2
O2
Inorganic
O3 h? ? O(1D) O2 O(1D) H2O ? 2 OH
RH OH ( O2) ? RO2 H2O RO2 NO ? RO
NO2 RO O2 ? RCHO HO2 RCHO OH ?
RC(O)O2 H2O RC(O)O2 NO ? NO2 RO2 CO2
Organic
HO2 NO ? OH NO2
OH NO2 ? HNO3 HO2 HO2 ? H2O2
Inorganic
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RADM2
Molecule based lumping VOC classes are based on
similarity in oxidation reactivity and emission
magnitudes. Each VOC category is represented by
several model species that span the required
reactivity range. Most emitted VOCs are lumped
into model species of similar reactivity and
molecular weight. Some VOCs with very large
emissions are treated as separate model species.
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RADM2
Reactivity weighting takes into account
differences in reactivity within a model species
(Middleton et al., 1990)
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RADM2
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RADM2
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RADM2
Peroxy radical Peroxy radical
reactions (general features)
HO2 XP ? OP1/OP2 MO2 XP ? aHCHO HO2
bALD cKET ACO3 XP ? aALD bKET cHO2
dMO2 eORA2
XP organic peroxy radicals
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RADM2
Chemical kinetics

• Gas-phase chemistry can be described by a set of
  ODEs

Pi production term ciLi loss term

• Numerical soultion based on an QSSA assumption
• Fast species

Slow species
(backward Euler)
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(No Transcript)
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MADE/SORGAM
Modal representation of the size distribution
(log-normal)
The kth moment of the distribution is defined as
with the solution
M0 number of aerosol particles M2 is
proportional to the total particulate surface
area M3 is proportional to the total particulate
volume
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MADE/SORGAM
Conservation equation
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MADE/SORGAM
Nucleation
Homogeneous nucleation in the sulfuric acid-water
system.
Condensation
Two steps production of condensable material
(vapor) by the reaction of chemical precursors
and condensation and evaporation of ambient
volatile species on aerosols. Kelvin effect is
neglected. Calculation of the time rate of change
of a moment Mk for the continuum and
free-molecular regime.
Coagulation
Distributions remain log-normal. Only effects
caused by Brownian motion are considered.
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MADE/SORGAM
Chemistry
Inorganic
Composition of a sulphate/nitrate/ammonium/water
aerosol on equilibrium thermodynamics.
particle
gas
Organic
4 x SOA anthropog.
? OH O3 NO3 ?
4 Products
HC OLT XYL OLI TOL CSL API LIM
4 x SOA biog.
4 Products
The gas/particle portioning of SOA compounds are
parameterized according to Odum et al., 1996
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WRF/Chem Emissions(Anthropogenic)
Gas phase e_so2, e_no, e_ald, e_hcho, e_ora2,
e_nh3, e_hc3, e_hc5, e_hc8, e_eth, e_co, e_ol2,
e_olt, e_oli, e_tol, e_xyl, e_ket, e_csl, e_iso,
Aerosols e_pm25i, e_pm25j, e_so4i, e_so4j,
e_no3i, e_no3j, e_orgi, e_orgj, e_eci,
e_ecj,e_pm10
Emissions are in mol/km2/hr
We need to map from emission to WRF grid
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Sample code
data ename/ 'e_so2 ','e_no ','e_ald
','e_hcho','e_ora2', 2 'e_nh3 ','e_hc3
','e_hc5 ','e_hc8 ', 3 'e_eth ','e_co
','e_ol2 ','e_olt ','e_oli ','e_tol ','e_xyl ',
4 'e_ket ','e_csl ','e_iso ','e_pm25i','e_pm25j
', 5 'e_so4i','e_so4j','e_no3i','e_no3j','e_o
rgi','e_orgj','e_eci', 6 'e_ecj','e_pm10'/ C
Open output files, 7 print and log, 19
unformatted wrf output OPEN(19,FILE'wrfem12
k_00to12Z',FORM'UNFORMATTED')
WRITE(19)NRADM WRITE(19)ename DO 172
IHR1,24 ! hour WRITE(19)IHR
DO N1,NRADM C Write out 3-D emission arrays to
unformatted file DO I1,IX2
DO K1,KX DO J1,JX2
EM3RS(I,K,J)EM3RD(I,K,J,N)
ENDDO ENDDO ENDDO
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WRF/Chem Emissions(Biogenic)
sebio_iso, sebio_oli, sebio_api, sebio_lim,
sebio_xyl, sebio_hc3, sebio_ete, sebio_olt,
sebio_ket, sebio_ald, sebio_hcho, sebio_eth,
sebio_ora2, sebio_co, sebio_nr, noag_grow,
noag_nongrow, nononag
Emissions are in mol/km2/hr