February 14, 2001, SCOS97-NARSTO DataWorkshop

Center for Environmental Research and Technology/Environmental Modeling

University of California at Riverside

Data Needs for Evaluation of Radical and Data Needs for Evaluation of Radical and NOy Budgets in SCOS97-NARSTO Air NOy Budgets in SCOS97-NARSTO Air

Quality Model SimulationsQuality Model Simulations

February 14, 2001, SCOS97-NARSTO DataWorkshop

Gail S. Tonnesen

University of California, RiversideBourns College of Engineering

Center for Environmental Research and Technology



AcknowledgmentsAcknowledgments

• Funding for related projects– U.S. EPA– American Chemistry Council

• Datasets – Draft prerelease datasets provided by ARB



Trace Gas Governing EquationsTrace Gas Governing Equations

• j=1,N Coupled PDEs

Cj t v.Cj + D2Cj + P(C) L(C)Cj + Ej Dj

• Operator Splitting:

Cj t = v.Cj

Cj t = D2Cj + Ej Dj

dCj dt = P(C) L(C)Cj

Gear solver is the gold standard for stiff ODEs



Model EvaluationModel Evaluation

• Verification, Validation or Evaluation?– Oreskes et al., 1994.

• Comparisons with ambient data.

• Validation of component processes.

• Indicators for testing O3 sensitivity.

• Sensitivity and uncertainty analysis.



Family DefinitionsFamily Definitions

NOx = NO + NO2 + (NO3 + 2 N2O5 + HONO + HNO4)

NOz = HNO3 + RNO3 + NO3– + PAN

NOy = NOx + NOz = total oxidized nitrogen.

HC = VOC (or ROG) + CH4 + CO

Ox = O3 + O + NO2 + NOz + 2 NO3 + 3 N2O5 + HNO4

HOx = OH + HO2 + RO2



Fundamental PhotochemistryFundamental Photochemistry

Tropospheric gas phase chemistry is driven by the OH radical:

• Radical Initiation

• Radical Propagation

• Radical Termination

• NOx termination



PSS EquilibriumPSS Equilibrium

NO2 + h NO + O

O + O2 O3

O3 + NO O2 + NO2

NO2 + O3 NO3 + O2

NO3 + h NO2 + O

P(Ox): RO2 + NO RO + NO2

HO2 + NO OH + NO2



Radical InitiationRadical Initiation

O3 + h O(1D)

O(1D) + H2O 2 OH

HCHO + h 2 HO2 + CO HO2 + NO OH + NO2

HONO + h OH + NO

PAN RO3 + NO2



Radical PropagationRadical Propagation

OH + CH4 + O2 CH3 O2 + H2O

CH3O2 + NO NO2 + CH3O

CH3O + O2 HO2 + HCHO

HO2 + NO NO2 + OH

2x( NO2 + h + O2 O3 + NO )

Net Reaction:

CH4 + 4 O2 2 O3 + HCHO + H2O



Radical and NORadical and NOxx termination termination

OH + NO2 HNO3

HO2 + HO2 H2O2

HO2 + RO2 ROOH

RO2 + NO RNO3

RO3 + NO2 PAN

N2O5 + H2O 2 HNO3



• Local Diagnostics– Instantaneous reaction rates at a given site.

– Examples: P(OH), P(Ox), P(Ox)/P(NOz)

– Cannot get production rates from time-series!

• Cumulative Trajectory Diagnostics– cumulative history of reaction rates and other

loss processes in an air parcel integrated over hours or days.

– Examples: [H2O2], [HNO3], [O3], [O3]/[NOz]

Model EvaluationModel Evaluation



• Radical Initiation J-values & HCHO, O3, H2O, HONO, H2O2, PAN

• OH Chain Length

kOH HCi /( kOH HCi + kOH NO2 )

kHO2 NO /(kHO2 NO + kHO2 (RO2+ 2 HO2 ) )

• Radical TerminationNO2 & OH, HO2 & RO2, NO & RO2, O3

• NOx Termination, P(NOz):NO2 & OH, NO & RO2, NO2 & RCO3, NO3, N2O5 & H2O

• Pg(Ox)

NO, HO2, RO2.

Data Needs for Local DiagnosticsData Needs for Local Diagnostics



• Radical Initiation & Termination (approximate):Radical Initiation & Termination (approximate): (2 peroxides + NO(2 peroxides + NOz z ))

• OH Chain Length (approximate):OH Chain Length (approximate):OOx x / (2 peroxides + NO/ (2 peroxides + NOz z ))

2 peroxides/NO2 peroxides/NOz z

• NONOxx Termination, P(NO Termination, P(NOzz):):

HNOHNO33, speciated RNO, speciated RNO33, NO, NO33--,, PAN PAN

• P(OP(O33), P(O), P(Oxx):):

OO33, & O, & O33 +NO +NO22 + NO + NOzz

Data Needs for Cumulative DiagnosticsData Needs for Cumulative Diagnostics



Model Domain and ParametersModel Domain and Parameters

• 1997 Southern California Ozone Study (SCOS97). Aug 3 to 5, 1997

• CMAQ and CAMx

• MM5 16 layers

• CB4 chemical mechanism

• Gear CMAQ, CMC CAMx

• Bott Advection Scheme

• No Aerosols

• Includes process analysis diagnostic outputs.



Uncertainties In CMAQ vs CAMx Uncertainties In CMAQ vs CAMx ComparisonComparison

• Timing in CAMx - are emissions calculated as PST or PDT?

• Vertical mixing - CAMx has less vertical dispersion in early morning?

• Emissions - CMAQ may be missing large point sources.

• Problem with isoprene in CAMx



Peak Model Ozone on Aug 5 (3rd day)

Difficult to analyze effects accumulated over 3 days, so...



Start Evaluation with spinup (1st day) Comparison of O3 at 15:00 PDT:



Comparison of O3 aloft before start of 2d day

Errata: all units are ppbV



Pg(Ox) 7:00-8:00 PDT



Pg(Ox) 8:00-9:00 PDT



Pg(Ox) 9:00-10:00 PDT



Pg(Ox) 10:00-11:00 PDT



Pg(Ox) 11:00-12:00 PDT



Cumulative Pg(Ox) 7:00-19:00 PDT



CO conc. at 9:00 PDT in LA: inversion breaks up 2 hours later in CAMx…is timing of emissions wrong?



Cumulative P(OH) 7:00-19:00 PDT, Aug 3.



H2O at 12:00 PDT



% contribution of O1D to OH initiation, cumulative for Aug 3.



HO2 initiation, cumulative for Aug 3.



RO2 radical initiation, cumulative for Aug 3.



Reactions of NO3 & O3 with isoprene, cumulative for Aug 3.



Reactions of OH with isoprene, cumulative for Aug 3.



Total new radical initiation, Layer 1, cumulative for Aug 3.



Total OH Production, Layer 1, cumulative for Aug 3.



HNO3 mixing ratio, 24:00 PDT, Aug 5.



HNO3 produced by OH+NO2, Layer 1, cumulative for Aug 5.



HNO3 produced by OH+NO2, Later 3, cumulative for Aug 5.



HNO3 produced by N2O5+H2O, cumulative for Aug 5.



E-W Slice through LA, cumulative for Aug 5.



Fraction HNO3 of total NOz, cumulative for Aug 5.



Net Production of PAN, cumulative for Aug 5.



Production of organic nitrates, cumulative for Aug 5.



Total Production of NOz, cumulative for Aug 5.



Ox production efficiency per NOx, cumulative for Aug 5. (Note: regions of gray within red are areas in which P(NOz) is negative).



Indicators to Evaluate O3 SensitivityIndicators to Evaluate O3 Sensitivity

• Indicators based on HNO3 or NOz may fail in CAMx simulations due to large contribution of N2O5+H2O to P(HNO3).

• Alternative: Use indicators based on radical propagation efficiency, O3 is VOC sensitive for:

%HO2+NO > 93%

%OH+HC < 80%



Indicator of O3 sensitivity: %HO2+NO (cumulative for Aug 5).



Indicator of O3 sensitivity: %OH+HC (cumulative for Aug 5).(Note colormap is inverted)



ConclusionsConclusions

• Minor problems with emissions, vertical dispersion and time zone need to be corrected before full evaluation.

• More serious issue w.r.t. N2O5 chemistry.

• Uncertainty in fate of NOx is a critical issue for

O3 sensitivity and weekend effects.

• Validation of HOx budgets is equally important.



RecommendationsRecommendations

• Should adopt an up-to-date mechanism

– SAPRC99, CB4-99, RACM2.

• Use NOy data to better characterize N2O5

chemistry and NOx fate.

• Use sensitivity studies to evaluate effects of uncertainty in N2O5 chemistry.

February 14, 2001, SCOS97-NARSTO DataWorkshop

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