Draft V.0 April 28, 2005

			

Development of CMAQ Boundary Conditions 

Bureau of Air Quality Analysis and Research

Division of Air Resources

New York State Department of Environmental Conservation

Albany, NY 12233

One of the inputs needed for performing CMAQ simulation is the
concentration field along the boundaries commonly referred to as
boundary conditions (BCs). In prior regional photochemical modeling
simulations covering extended episodes often utilized ‘clean’ BCs. 
Recognizing that pollutant influx arising from the upwind regions are
varying and dynamic especially for grid modeling applications covering
seasonal and annual simulations the use of global chemical transport
models such as GEOS-CHEM of Harvard University (  HYPERLINK
"http://www-as.harvard.edu/chemistry/trop/geos/index.html" 
http://www-as.harvard.edu/chemistry/trop/geos/index.html ) and MOZART of
National Center for Atmospheric Research (NCAR) (  HYPERLINK
"http://www.acd.ucar.edu/science/gctm/mozart/index.php" 
http://www.acd.ucar.edu/science/gctm/mozart/index.php ) Byun et al
(2004) has proposed developing BCs  which had been applied in some of
the current modeling exercises (EPA, 2004, 2005). 

In this note we describe the development of the BCs for the OTC Modeling
Committee application of CMAQ at 36 km grid spacing and perform a
limited comparison with the BCs reported for Visibility Improvement
State and Tribal Association of the Southeast’s (VISTAS) modeling
domain. GEOS-CHEM simulation data for 2002 were obtained through the
efforts of the Northeast Consortium of Air Use Management (NESCAUM) in
December 2004. The GEOS-CHEM simulation data were at the spatial
resolution of 4˚ by 5˚ in the horizontal and 20 layers in the vertical
extending from surface to about 100 mb. The model provides information
for about 50 chemical gas and particulate matter species. We utilized a
modified version of the GEOS-CHEM to CMAQ interface program (Moon and
Byun, 2004) so as to match the OTC 36 km modeling domain. To provide an
added level of confidence in the development of the BCs, a comparison
was performed with the BCs reported for the VISTAS 36 km modeling
domain. It should be noted that the two domains differ in their
definition with the OTC domain being smaller horizontally and has more
layers in the vertical when compared with the VISTAS domain.

 

Spatial patterns of Ozone and SO4

Figure 1 displays ozone concentrations in layer 1 along the boundaries
for OTC and VISTAS domains at hour 15 on August 13, 2002. Although the
OTC domain is slightly smaller than VISTAS domain, both exhibit similar
maximum level of concentration of about 70 ppb. The OTC domain had
slightly higher peak ozone (168 ppb) at the top of the domain along the
boundaries than VISTAS (see Figure 2), which has a maximum of 139 ppb.
This is not unexpected since the top layer of the OTC domain is higher
than VISTAS domain.  Figure 3 shows similar displays for SO4 at the
boundary at the lowest layer of the OTC and VISTAS domains.

Averaged Ozone and SO4 concentrations at the boundaries of the modeling
domain

Table 1 lists the averaged ozone concentrations at surface and for the
whole boundary layer,  (OTC domain with 22 layers, and VISTAS domain
with 19 layers), at each one of the four boundaries for August 2002. In
both cases the concentrations exhibit similar pattern, with higher
concentrations at south and east boundaries and low concentration in the
north and west boundaries. Table 2 is similar to Table 1, except it
lists SO4 concentrations. The higher SO4 boundary conditions at the
eastern boundary are suspected to be due to the outflow from the US
continent.

Averaged Ozone and SO4 BC vertical profiles from each of the domain

Figure 4 displays the average vertical profile of ozone concentrations
at each of four boundaries for August 2002. As to be expected, GEOS-CHEM
yields increasing ozone concentrations with increasing altitude and this
is reflected in Figure 4. Figure 5 displays the average vertical profile
of SO4 concentration at each of the four boundaries. 

Conclusions

Boundary conditions based upon (GEOS-CHEM) were generated for the period
of May through September 2002 for use in the 36 km CMAQ modeling
simulations. Comparison of the BCs with those developed by VISTAS
indicates good agreement.

 

References

Byun, D. W., Moon, N. K., Jacob, D., and Park, R. (2004) Regional
transport study of air pollutants with linked global tropospheric
chemistry and regional air quality models. 2nd ICAP Workshop, Research
Triangle Park, NC

  HYPERLINK
"http://www.cep.unc.edu/empd/projects/ICAP/2004wkshp_pres.html" 
http://www.cep.unc.edu/empd/projects/ICAP/2004wkshp_pres.html .

EPA (2004): Use of GEOS-CHEM for CMAQ Boundary Conditions,   HYPERLINK
"http://www.epa.gov/air/interstateairquality/pdfs/GEOSCHEMforCMAQ_Descri
ption.pdf" 
http://www.epa.gov/air/interstateairquality/pdfs/GEOSCHEMforCMAQ_Descrip
tion.pdf 

EPA (2005): Technical support document for the final clean air mercury
rule: Air quality modeling. USEPA, Research Triangle Park, NC

  HYPERLINK "http://www.epa.gov/camr/"  http://www.epa.gov/camr/ 

Moon N. K., and Byun, D. W. (2004) A simple User’s Guide for
“geos2cmaq” code: Linking CMAQ with GEOS-CHEM, Version 1.0,”
Interim report from Institute for Multidimensional Air Quality studies
(IMAQS) University of Houston, Houston TX

  HYPERLINK "http://www.math.unh.edu/~dwbyun/Meetings/icap/" 
http://www.math.unh.edu/~dwbyun/Meetings/icap/ .



Table 1: The average ozone concentrations (ppb) at each one of the four
boundaries for the OTC and VISTAS 36 km domains during August 2002

Boundary	OTC (22 layer avg) 	VISTAS (19 layer avg)	OTC (surface)	VISTAS
(surface)

South	43.9 	35.6 	36.8	31.6

East	52.2 	46.4 	40.5 	40.7

North	34.1 	21.9 	13.7	13.5

West	40.0 	32.9 	25.8	24.9



Table 2: The average SO4 concentrations ((g/m3) at each one of the four
boundaries for the OTC and VISTA 36 km domains during August 2002

Boundary	OTC (22 layer avg)	VISTAS (19 layer avg) 	OTC (surface)	VISTAS
(surface)

South	0.54	0.51	0.70	0.56

East	1.50	1.67	2.04	1.88

North	0.45	0.54	0.63	0.64

West	0.42	0.47	0.53	0.53



Figure 1: The lowest layer ozone concentrations (ppm) along the
boundaries for the                     OTC and VISTAS 36 km domain

Figure 2: The top layer ozone concentrations (ppm) along the boundaries
for the                     OTC and VISTAS 36 km domain

Figure 3: The lowest layer sulfate concentrations ((g/m3) along the
boundaries for the OTC and VISTAS 36 km domain

Figure 4: Averaged ozone concentrations (ppb) in the vertical along each
boundary of the OTC and VISTAS 36 km domain

Figure 5: Averaged sulfate concentrations ((g/m3) in the vertical along
each boundary of the OTC and VISTAS 36 km domain

 

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