An initial linkage of the CMAQ modeling system at neighborhood scales with a

human exposure model

Jason Ching/Thomas PierceAir-Surface Processes Modeling Branch

Atmospheric Modeling DivisionNational Exposure Research Laboratory

EPA Office of Research and Development

October 19, 2004

Collaborators EPA/OAQPS (T. Palma, J. Touma)

CSC (R. Tang, S. Edney, L. Bender)

EPA/ORD (W. Hutzell, D. Luecken) EPA/Region 3 (A. Cimorelli)

State of Delaware (R. Majeed)

AMD ResearchCommunity-scale modeling for air toxics

and homeland security

Objective: Develop numerical modeling tools for simulating ambient concentrations of airborne substances in urban settings at spatial scales ranging from <1-10 km for assessing human exposures.

Motivation: Tools are needed to assess the small-scale variability in ground-level concentrations that occurs from the release of toxic air pollutants in an urban setting. These tools can benefit the National Assessment of Air Toxics (NATA) program and other human exposure modeling programs.

Science Question

Can a chemical transport model (such as CMAQ) successfully augment traditional Gaussian plume modeling approaches for estimating annual ambient concentration estimates of air toxics for human exposure assessments in urban settings?

Study ApproachDevelopment of an initial prototype to support

human exposure models

• Establish collaborations with Delaware, Region 3, and OAQPS

• Use the 36 km CMAQ simulations for boundary conditions

• Apply CMAQ at 12 & 4 km to Philadelphia for 2001

• Compare CMAQ with available air toxic observations

• Link annual CMAQ results to HAPEM5

• Assess practicality of using CMAQ

CMAQ modeling domains (36, 12, 4 km)

Ethylene DichlorideAnnual average (2001)CMAQ

36 12 4

0.000

0.020

0.040

0.060

0.080

Eth

yle

ne

Dic

hlo

ride

(u

g/m

3)

Cell Size (km)

… impact of grid size on modeling air toxics in the Philadelphia area

1,3-ButadieneAnnual average (2001)CMAQ

36 12 4

0.000

0.050

0.100

0.150

0.200

0.250

0.300

Bu

tad

ien

e 1

3 (

ug

/m3

)

Cell Size (km)

BenzeneAnnual average (2001)CMAQ

36 12 4

0.000

0.500

1.000

1.500

2.000

2.500

Be

nze

ne

(u

g/m

3)

Cell Size (km)

AcetaldehydeAnnual average (2001)CMAQ

36 12 4

0.000

1.000

2.000

3.000

4.000

Ald

eh

yde

(u

g/m

3)

Cell Size (km)

FormaldehydeAnnual average (2001)CMAQ

36 12 4

0.000

1.000

2.000

3.000

4.000

Fo

rma

lde

hyd

e (

ug

/m3

)

Cell Size (km)

…while the means are comparable, the 4 km grids provide more spatial variability than the 12/36 km grids

CMAQ can differentiate primary and secondary formaldehyde in an urban area. The time series shows a 4 km grid cell (26,47) over central Philadelphia. Data are grouped into three-hour averages.

CMAQ simulation for central Philadelphia

0

5

10

15

20

25

0 50 100 150 200 250 300 350

Day of year (2001)

Fo

rmal

deh

yde

(ug

/m3)

Secondary

Primary

Comparison of air toxic concentrations measured at the Camden, NJ, site to CMAQ (layer 1). All samples, except

benzene, are 24-hour averages; benzene is a 1-hour average.

Mean (ug/m3) Std. deviation (ug/m3)

Compound n Obs 4 km 36 km Obs 4 km 36 km

1,3-Butadiene 28 0.33 0.18 0.12 0.34 0.12 0.08

Formaldehyde 44 3.68 2.91 2.25 3.21 2.13 1.52

Acetaldehyde 44 2.09 2.49 1.92 1.42 1.20 0.78

Benzene 1328 1.11 1.02 0.77 1.06 0.71 0.40

…based on this limited comparison, CMAQ compares favorably to observations

Linkage of annual CMAQ results to HAPEM5

• Hazardous Air Pollutant Exposure Model (HAPEM5)› Screening-level exposure model› Predicts “apparent” inhalation for general population in a census tract› Attempts to account for behavior of demographic groups for indoor and outdoor microenvironments› Uses annual 3-hr average ambient concentrations assumed at the centroid of each census tract› Ingests statistical distribution info (median, mean, and 90th-percentile)

• CMAQ results› Aggregated into annual 3-hr time bins› Concentration distribution from the grid cell overlaying a centroid was used in HAPEM5

CMAQ 36 KM Formaldehyde

0 10

Scale in K ilom eters

1 inch on m ap = 4.03 kilom eters

HAPEM 5 Concentration (ug/m 2)

0 - 0.5

0.5 - 1

1 - 1.5

1.5 - 2

2 - 2.5

2.5 - 10

CMAQ 12 KM Formaldehyde

0 10

Scale in K ilom eters

1 inch on m ap = 4.03 kilom eters

HAPEM 5 Concentration (ug/m 2)

0 - 0.5

0.5 - 1

1 - 1.5

1.5 - 2

2 - 2.5

2.5 - 10

CMAQ 4 KM Formaldehyde

0 10

Scale in K ilom eters

1 inch on m ap = 4.03 kilom eters

HAPEM 5 Concentration (ug/m 2)

0 - 0.5

0.5 - 1

1 - 1.5

1.5 - 2

2 - 2.5

2.5 - 10

HAPEM5 results for Philadelphia based on CMAQ annual (2001) simulations

Formaldehyde (mean)

CMAQ 36 KM Formaldehyde (90P)

0 10

Scale in K ilom eters

1 inch on m ap = 4.03 kilom eters

H APEM 5 C oncentration(ug/m 3)

0 - 1

1 - 2

2 - 3

3 - 4

4 - 5

5 - 6

CMAQ 12 KM Formaldehyde (90P)

0 10

Scale in K ilom eters

1 inch on m ap = 4.03 kilom eters

H APEM 5 C oncentration(ug/m 3)

0 - 1

1 - 2

2 - 3

3 - 4

4 - 5

5 - 6

CMAQ 4 KM Formaldehyde (90P)

0 10

Scale in K ilom eters

1 inch on m ap = 4.03 kilom eters

H APEM 5 C oncentration(ug/m 3)

0 - 1

1 - 2

2 - 3

3 - 4

4 - 5

5 - 6

HAPEM5 results for Philadelphia based on CMAQ annual (2001) simulations

Formaldehyde (90th-percentile)

Average Philadelphia exposure levels (ug/m3) computed with HAPEM5

CMAQ 4 km NATA

CompoundMedian

DDMean DD 90% DD Mean

DD

Benzene 0.96 1.26 2.63 2.23

Formaldehyde 1.63 2.15 4.60 2.57

*DD = Diurnal Distribution

… CMAQ can be used to provide statistical distributions to human exposure models.

Is it practical to apply CMAQ to model air toxics in urban areas?

• Annual simulation on EPA’s IBM eServer Cluster 1600 (w/ 8 CPUs):

- 12 km (45 x 45 grid cells): 55 hours- 4 km (54 x 72 grid cells): 146 hours

• Simulation times on a Linux cluster are comparable

• With modern computer resources, annual urban simulations are quite manageable

Future opportunities for linking CMAQ to human exposure models at urban scales

• Integrate approach with ISCST or AERMOD

• Extend capability to a finer grid resolution (~1 km)

• Perform more extensive model evaluation

• Link with the SHEDS human exposure model

• Explore application to other regions for other toxics

An initial linkage of the CMAQ modeling system at neighborhood scales with a

human exposure model

Disclaimer: This research was performed under the Memorandum of Understanding between the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Commerce’s National Oceanic and Atmospheric Administration (NOAA) and under agreement number DW13921548. Although this work was reviewed by EPA and NOAA and approved for publication, it may not necessarily reflect their policies or views.

For more information: pierce.tom@epa.gov