Modeling Toxic Industrial Chemicals (TICs) and CWAsModeling Toxic Industrial Chemicals (TICs) and CWAs Using an Atmospheric Chemistry Module in SCIPUFFUsing an Atmospheric Chemistry Module in SCIPUFF

Douglas S. Burns, Veeradej Chynwat, Jeffrey J. Piotrowski, Kia Tavares, and Floyd L. Wiseman ENSCO, Inc., Melbourne, FL

BackgroundThe goal of this DTRA sponsored project was to generate a set of polynomial functions that describe the atmospheric degradation rates for typical Toxic Industrial Compounds (TICs). Atmospheric degradation rates generally depend upon a variety of meteorological parameters such as the time of day, zenith angle, relative humidity, temperature, and ambient conditions. The largest rate processes for most organic species include the reactions with hydroxyl radical (OH), ozone (O3), and nitrate radical (NO3). Current atmospheric models, such as the Carbon Bond Mechanism (CBM), account for the reactions with these indigenous species, as well as reactions with other species, and often these models contain over a hundred chemical reactions and close to a hundred different chemical species. The computer code for generating the concentration profiles for the TICs/CWAs requires solving a large system of ordinary differential equations (ODEs), that is computationally intensive. The benefit of replacing this large set of ODEs with a set of polynomial functions is in saving both cpu and wall clock run time. The drawback is some loss of precision by using the simpler polynomials.

ENSCO, Inc. has developed polynomial functions for describing the atmospheric degradation rate constants for a series of Alkenes (e.g., 1-butene and 2-methylpropene), H2S, and Sarin. The parameters in the polynomials are obtained by fitting the polynomials against model-generated data. The polynomials are then incorporated into the SCIPUFF T&D Model as part of an atmospheric chemistry module in HPAC. Tests were conducted to ensure that model run time is not affected by incorporating the chemistry module. 1-butene is fairly reactive, as are many other TICS, and so the effect of including a chemistry module will be to reduce the toxic footprint for a release of 1-butene. The methodology described here has been developed and can be readily applied to any atmospheric pollutant.

OH

NO3

NOX

TICs

O3

H2O

Pollutant + OH, NO3, O3, etc.

kOH, kNO3

, kO3,

etc.

Degradation products

Transport, diffusion, and chemical reactivity

Concept

Strategy• Implement Algorithm into SCIPUFF / HPAC

Develop a chemistry module (currently called degrade.dll) that interfaces with the dispersion algorithms in SCIPUFF.

• Develop data for algorithm for the atmospheric degradation of TICs / CWAs Requirements specified for development of the chemistry algorithm:

The algorithm must run rapidly and not impact model wall clock run-time The algorithm must account for all modeling scenarios encompassing a wide range of

meteorological conditions (i.e., changes in cloud cover, temperature, ambient conditions, etc.).

The algorithm must be robust enough to account for diurnal changes to the degradation rates of TICs and CWAs.

The algorithm should account for the potential generation of intermediate toxic compounds. In some cases it may be possible for the degradation products to be more toxic than the pollutant that was released.

Data Development Translate C(t) data to keff using the following: Fit keff data to a series of polynomials and determine the best polynomial function. The polynomial algorithms are a function of meteorological parameters (i.e., T, SE,

CC, time of day, [H2O], etc., and ambient concentrations of indigenous atmospheric species (OH, O3, VOCs, NO3). Ambient concentrations are associated with five super classes of Land Use (Urban, Grassland, Forest, Desert, and Water)

][

][

CtC

keff

CH2=CHCH2CH3 + OH 0.94 C2H5CHO(1-butene)

CH2=CHCH2CH3 + NO3 0.6 CH3CH2–CH(OH)—CH2ONO2

0.12 C2H5CHO + 0.11 H2CO

CH2=CHCH2CH3 + O3 0.35 C2H5CHO + 0.63 H2CO + 0.41OH

Rate = -(kOH[OH] + kNO3[NO3] + kO3

[O3]) [1-butene]

Rate = -keff [1-butene]

TIC: Atmospheric Reactions of 1-butene

kOH

kNO3

kO3

CWAs

Plume contours of 1-butene and propanal (product) at 4 and 8 hrs afterrelease (Urban scenario for 2 hour continuous release of 1-butene)

1-butene propanal

Tracking of Reactant and Product(s)

API

SCIPUFF Function Library Plottool

Interface Functions

FileManager

PlotManager

ProjectManager

Dispersion

MeteorologyGenerator

SWIFT

MC-

SCIPU

FF

FileReaders

UtilityFunctions

PlotGenerator

EffectsManager

EffectM

odule

EffectM

odule

DEGRADE DLL

API

SCIPUFF Function Library Plottool

Interface Functions

FileManager

PlotManager

ProjectManager

Dispersion

MeteorologyGenerator

SWIFT

MC-

SCIPU

FF

FileReaders

UtilityFunctions

PlotGenerator

EffectsManager

EffectM

odule

EffectM

odule

DEGRADE DLL

SCIPUFFDispersion

XT(x,y,t) = ∫ fA c(x,y,0,t) dtt

0

= -kA fAdfAdt

kA = max(kA sin(), kA )(max) (min)

kA = keff = f(, T,cc, [amb], humidity, etc.)

Modification to the chemistry algorithm in SCIPUFF.

CH3-P(=O)(-F)(-CH(CH3)2) + OH Degradation Product (Sarin)

CH3-P(=O)(-F)(-CH(CH3)2) + NO3 Degradation Product

Rate = -(kOH[OH] + kNO3[NO3]) [Sarin]

Rate = -keff [Sarin]

CWA: Atmospheric Reactions of Sarin (GB) kOH

kNO3

Run Photochemical Box Model (PBM)

or

NOX

VOC’s

O3CO

Location (lat, lon)

ZA = f(Lat, Lon, DOY, Time of day)

H2O

][

][

butenet

butene

keff

[Butene] as f(time of day)T = 290 KLand use = Urban

Latitude = 25 – 50° N

Time of day [hrs from midnight]

[But

ene]

[ppm

]

25°

50°

Decomposition of Butene as f(Latitude)

Decomposition of GB as f(Temperature)

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

0 180 360 540 720 900 1080 1260 1440

Time of day [min from midnight]

GB

Con

cent

ratio

n [p

pm]

310300290280270

25º

50º

keff as f(time)

Lat = 25 – 50º N

k eff

[min

-1]

Mechanism ID Rxn’s, EA, k(T)

(w/ OH, NO3, H2O, O3, etc.)

Implement TIC / CWAData in Detailed

Model such as theCBM

Run Photochemical Box Model (PBM)

as a f(met parm’s)

Obtain cTIC(t) as

f(met parm’s)

Derive Empiricalkeff (met parm’s)

Populate SCIPUFF w/ keff data

Implementation of Algorithm in SCIPUFF

Develop Chemical Data for TICs / CWAs

Generate c(t) data

Translate to keff

Example Results

SCIPUFF

Tracer 1-Butene

Figure 1. Plume comparison showing no degradation (using a tracer) and degradation (using 1-butene) between the SCIPUFF and ChemCODE models for the grass land use.

T&D Only vs T&D + Chemistry

3-Methyl Propene

1,3-Butadiene

Ethene Propene

Calculated Plume is TIC Dependent

Summary An atmospheric chemistry capability that does not impact model run time was incorporated into SCIPUFF. Algorithms were developed for the atmospheric degradation of nine alkenes, H2S, and Sarin.

The effective degradation rates (keff) for TICs and CWAs are describe by a series of developed polynomial functions that are a function of important meteorological parameters• Temperature, solar elevation, cloud cover, time of day, moisture level, latitude, ambient conditions (Land use is used as a surrogate for air quality)

The algorithm can account for the formation of degradation products (e.g., propanal from 1-butene) Future plans are to increase the data base to include other TICs and CWAs.