February 14, 2001, SCOS97-NARSTO DataWorkshop

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Data Needs for Evaluation of Radical and NOy Budgets in SCOS97-NARSTO Air Quality Model Simulations. Gail S. Tonnesen University of California, Riverside Bourns College of Engineering Center for Environmental Research and Technology. February 14, 2001, SCOS97-NARSTO DataWorkshop.

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

Gail S. Tonnesen

University of California, Riverside

Bourns College of Engineering

Center for Environmental Research and Technology

February 14, 2001, SCOS97-NARSTO DataWorkshop

Funding for related projects

U.S. EPA

American Chemistry Council

Datasets

Draft prerelease datasets provided by ARB

Acknowledgments

Trace Gas Governing Equations

• j=1,N Coupled PDEs

Cj t  v.Cj + D2Cj + P(C)  L(C)Cj + Ej  Dj

• Operator Splitting:

Cj t = v.Cj

Cj t = D2Cj + Ej  Dj

dCj dt = P(C)  L(C)Cj

Gear solver is the gold standard for stiff ODEs

Model 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 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 Photochemistry

Tropospheric gas phase chemistry is driven by the OH radical:

• NOx termination

PSS 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

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

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

OH + NO2  HNO3

HO2 + HO2 H2O2

HO2 + RO2 ROOH

RO2 + NO RNO3

RO3 + NO2 PAN

N2O5 + H2O  2 HNO3

Model Evaluation

• 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]

Data Needs for Local Diagnostics

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 ) )

NO2 & 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 Cumulative Diagnostics

• Radical Initiation & Termination (approximate):

(2 peroxides + NOz )

• OH Chain Length (approximate):

Ox / (2 peroxides + NOz )

2 peroxides/NOz

• NOx Termination, P(NOz):

HNO3, speciated RNO3, NO3-, PAN

• P(O3), P(Ox):

O3, & O3 +NO2 + NOz

Model 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
• No Aerosols
• Includes process analysis diagnostic outputs.
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

Uncertainties In CMAQ vs CAMx Comparison

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:

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?

Ox production efficiency per NOx, cumulative for Aug 5.

(Note: regions of gray within red are areas in which P(NOz) is negative).

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%

Indicators to Evaluate O3 Sensitivity

(Note colormap is inverted)

Conclusions

• 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.

Recommendations

• 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.