Transcript CB05-TU – CB05-Base

Impact of an updated toluene mechanism on air
quality in the western US
Golam Sarwar, Wyat Appel, Annamrie Carlton, Rohit Mathur,
Keneth Schere, Mohammed Majeed
October 11, 2010
Office of Research and Development
Laboratory, Atmospheric Modeling and Analysis Division
National Exposure Research Laboratory
Background
• Chemical mechanisms are a critical component of air quality models
• Toluene is an imporant chemical compound that can affect O3 and SOA; however its
chemistry is poorly understood
• Different chemical mechanisms use different approximations for toluene chemistry
• Models using different chemical mechanisms produce different results
– Faraji et al. (2008) noted CB-IV & SAPRC99 lead up to 40 ppbv O3 difference in Houston
•
A large part of the difference was attributed to differences in aromatic chemistry
– Whitten et al. (2010) updated the toluene chemistry in CB05 (Whitten et al., 2010. A new condensed
toluene mechanism for Carbon Bond: CB05-TU, AE)
Office of Research and Development
Laboratory, Atmospheric Modeling and Analysis Division
National Exposure Research Laboratory
Background
• Chemical mechanisms are evaluated using chamber experimental results
– updated toluene chemistry performed better than base chemistry
• Earlier, we evaluated impact of the updated toluene chemistry on air quality in the
eastern US (Sarwar et al., 2010)
– Monthly mean 8-hr O3 increased by up to 2.0 ppbv
• Here, we examine impact of the updated toluene chemistry on O3 and PM in the
western US
Office of Research and Development
Laboratory, Atmospheric Modeling and Analysis Division
National Exposure Research Laboratory
Existing toluene chemistry in CB05 mechanism
CB05-Base (simplified)
TOL
OH
36%
56%
CRES
HO2
(benzaldehyde)
TO2
OH
HO2
8%
NO
OPEN
90%
10%
NTR
CRO
OH
NO2
NTR
NO2
C2O3
PAN
Ref: Yarwood et al., 2005
Office of Research and Development
Laboratory, Atmospheric Modeling and Analysis Division
National Exposure Research Laboratory
Updated toluene chemistry in CB05 mechanism
CB05-TU (simplified)
TOL
OH
18%
7%
OH
65%
CRES
HO2
NO
OPEN
CRO
NO2
NO
OH
2 NTR
86%
14%
OH
CRON
NO2
HO2
(benzaldehyde)
TO2
OH
CRNO
10%
O3
OPO3
NO2
NTR
OPAN
CRN2
OH
CRPX
Office of Research and Development
Laboratory, Atmospheric Modeling and Analysis Division
National Exposure Research Laboratory
Ref: Whitten et al., 2010
Modeling details
CMAQ model
• CMAQ model version 4.7 was used
• Horizontal grid resolution = 12-km
• Number of horizontal grids = 213 X 192
• Number of vertical layers = 14
• Surface layer thickness = 36 meter
• Simulation period: July 1 – 31, 2002
• Two different model simulations were performed
– with CB05-Base
– with CB05-TU
• Used generalized Rosenbrock solver for gas-phase chemistry
– Model with CB05-TU required 6% additional computational time
Office of Research and Development
Laboratory, Atmospheric Modeling and Analysis Division
National Exposure Research Laboratory
Modeling details
Meteorology and emissions
• Meteorological fields
– PSU/NCAR MM5 system
• Anthropogenic emissions
– 2002 National Emissions Inventory (NEI)
• Biogenic emissions
– Biogenic Emissions Inventory System (BEIS)
• Model-ready emissions
– Sparse Matrix Operator Kernel Emission (SMOKE)
Office of Research and Development
Laboratory, Atmospheric Modeling and Analysis Division
National Exposure Research Laboratory
CMAQ: impact on daily maximum 8-hr O3
Monthly mean 8-hr O3
(CB05-Base)
ppbv
Changes in mean 8-hr O3
(CB05-TU - CB05-Base)
Mean TOL/VOC
(CB05-Base)
ppbv
O3 increases where toluene/VOC ratio is high
Office of Research and Development
Laboratory, Atmospheric Modeling and Analysis Division
National Exposure Research Laboratory
CMAQ: variation of daily maximum 8-hr O3
(CB05-TU – CB05-Base)
Los Angeles
Portland
Seattle
While CB05-TU increases daily maximum 8-hr O3 by up to 5-6 ppbv,
impact on many other days are low to moderate
Office of Research and Development
Laboratory, Atmospheric Modeling and Analysis Division
National Exposure Research Laboratory
CMAQ: NOz with CB05-Base and increases in NOz with CB05-TU
Monthly mean NOz with CB05-Base
Changes in mean NOz
(CB05-TU - CB05-Base)
CB05-TU increases NOz compared to CB05-Base
Office of Research and Development
Laboratory, Atmospheric Modeling and Analysis Division
National Exposure Research Laboratory
CMAQ: ozone production efficiency (OPE)
CB05-Base at Los Angeles
CB05-TU at Los Angeles
CB05-TU increases O3 but not OPE
Office of Research and Development
Laboratory, Atmospheric Modeling and Analysis Division
National Exposure Research Laboratory
Comparison with observed data
Daily maximum 8-hr O3 at Seattle
MB with CB05-TU decreases slightly at higher observed O3 and increased
slightly at lower observed O3
Office of Research and Development
Laboratory, Atmospheric Modeling and Analysis Division
National Exposure Research Laboratory
Comparison with observed data
Daily maximum 8-hr O3 at Los Angeles
MB decreases slightly with CB05-TU at all observed O3
Office of Research and Development
Laboratory, Atmospheric Modeling and Analysis Division
National Exposure Research Laboratory
Impact on SOA from toluene
Monthly mean SOA with CB05-Base
CB05-TU / CB05-Base
Predicted SOA increased slightly with CB05-TU (maximum 7%)
However, impact on PM2.5 was also small
Office of Research and Development
Laboratory, Atmospheric Modeling and Analysis Division
National Exposure Research Laboratory
Summary
• Updated toluene chemistry enhances monthly mean 8-hr O3 by up to 2.8 ppbv
• Updated toluene chemistry produces more NOz than CB05-Base
• Updated toluene chemistry increase O3 but not OPE
• Updated toluene chemistry slightly decreases MB at higher observed O3
• Updated toluene chemistry slightly increases SOA; impact on PM2.5 is smaller
• Results are consistent with those reported by Sarwar et al. (2010) for eastern US
– CB05-TU increased monthly mean 8-hr O3 by up to 2.0 ppbv in eastern US
Office of Research and Development
Laboratory, Atmospheric Modeling and Analysis Division
National Exposure Research Laboratory