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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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Presentation Transcript
slide1

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

acknowledgments
Funding for related projects

U.S. EPA

American Chemistry Council

Datasets

Draft prerelease datasets provided by ARB

Acknowledgments
slide3

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

slide4

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.
slide5

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

slide6

Fundamental Photochemistry

Tropospheric gas phase chemistry is driven by the OH radical:

  • Radical Initiation
  • Radical Propagation
  • Radical Termination
  • NOx termination
slide7

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

slide8

Radical 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

slide9

Radical 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

slide10

Radical and NOx termination

OH + NO2  HNO3

HO2 + HO2 H2O2

HO2 + RO2 ROOH

RO2 + NO RNO3

RO3 + NO2 PAN

N2O5 + H2O  2 HNO3

slide14

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]
slide15

Data Needs for Local Diagnostics

  • 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 Termination

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.

slide16

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

slide17

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
  • Bott Advection Scheme
  • No Aerosols
  • Includes process analysis diagnostic outputs.
uncertainties in cmaq vs camx comparison
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
slide19

Peak Model Ozone on Aug 5 (3rd day)

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

slide20

Start Evaluation with spinup (1st day)

Comparison of O3 at 15:00 PDT:

slide27

Cumulative Pg(Ox)

7:00-19:00 PDT

slide28

CO conc. at 9:00 PDT in LA: inversion breaks up 2 hours

later in CAMx…is timing of emissions wrong?

slide47

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 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%

Indicators to Evaluate O3 Sensitivity
slide51

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.
slide52

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.
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