Prakash Bhave, Ann Marie Carlton, Sergey Napelenok, Tad Kleindienst, John Offenberg, Michael Lewandowski, Mohammed Jaoui

1
Evaluation of CMAQ for Precursor-Specific
Contributions to SOA in the Southeastern U.S.

• Prakash Bhave, Ann Marie Carlton, Sergey
  Napelenok, Tad Kleindienst, John Offenberg,
  Michael Lewandowski, Mohammed Jaoui
• CMAS Conference
• Chapel Hill, NC
• October 19 21, 2009

2
Overview

• Background
• Previous evaluations of CMAQ organic aerosol
• Revised SOA treatment in CMAQ v4.7
• Evaluation of current CMAQ results

3
CMAQ v4.5 Evaluation OC EC
Median Bias (µgC m-3)
Summary of performance at all eastern U.S sites
in 2001.Ref K.W. Appel, et al. (2008), Atmos.
Environ. 6057-6066.
4
Carbon Source Matrix
5
Model Eval. POA tracers (Jul99)
Modeled Observed Concentration
Bhave, Pouliot, Zheng, Environ. Sci. Technol.
(2007)
6
Radiocarbon Measurements (14C)

• Technique takes advantage of fact that 14C
  isotope is absent in fossil fuels
• PM2.5 samples collected at Nashville on June 21
  July 13, 1999 were analyzed for 14C

C.W. Lewis et al., Atmos. Environ. (2004)
7
Model Eval. Fossil-Fuel Carbon
8
Model Eval. Contemporary Carbon
9
Model Evaluation OC/EC Ratio

• Legend
• CMAQ results solid line empirical estimates
  dashed line
• OCsec is underestimated in the Southeast during
  summer
• OCsec is overestimated in the west-coast states

Yu, Bhave, Dennis, Mathur, Environ. Sci.
Technol. (2007)
10
Missing Source(s) in CMAQ?(Summer OC in
Southeast)
11
Tracer-Based Estimates of SOC

• Tracer-based method for estimating source
  contributions to ambient SOC
• Lab Experiments
• Smog chamber irradiations of numerous VOC/NOx
  mixtures
• Identified and quantified unique tracer compounds
  (e.g., methyl tetrols) using advanced GC/MS
  methods.
• Computed tracer/SOC ratios for each SOA precursor
  ( tracers 3 isop, 9 mono., 1 sesq., 1 arom.)
• Field Measurements
• Collected 33 PM2.5 samples in RTP throughout 2003
  (2 5 day duration)
• Quantified the same tracer compounds that were
  found in the chamber studies.
• Estimated ambient SOC contribution from each VOC
  precursor, using the tracer/SOC ratios.
• See Kleindienst et al. (Atmos. Environ., 41
  8288-8300, 2007) for details.

Greatest source of uncertainty - Are the
tracer/SOC ratios measured in the chamber equal
to those in the atmosphere? Approach - Accept
the tracer estimates at face value until better
information becomes available.
12
Tracer-Based Estimates
CMAQ v4.6 Results
Secondary Organic Carbon (µgC m-3)

• CMAQ v4.6 had
• the wrong seasonal cycle for total SOC
• too much monoterpene SOC (especially in Spring
  Fall)
• not enough aromatic SOC
• no isoprene or sesquiterpene SOC (also noted by
  Morris et al., 2006)

Kleindienst, Jaoui, Lewandowksi, Offenberg,
Lewis, Bhave, Edney, Atmos. Environ. (2007)
13
CMAQ v4.7
14
Did It Make a Difference?
CMAQ v4.6
new SOA treatment
Secondary Organic Carbon (µgC m-3)

• Model results from lowest layer are averaged by
  month
• 36km grid cell containing Research Triangle Park
  measurement site

15
Did It Make a Difference?
CMAQ v4.6
new SOA treatment
Secondary Organic Carbon (µgC m-3)

• Model results from lowest layer are averaged by
  month
• 36km grid cell containing Research Triangle Park
  measurement site

16
Model Evaluation for 4 SOC Classes
Tracer-Based Estimates
CMAQ new SOA

• Model results are consistently low (29 out of 33
  samples), especially during high-pollution
  episodes in Summer

17
Model Evaluation for 4 SOC Classes
CMAQ Model Results µgC m-3
Tracer-Based Estimates µgC m-3
18
Summary

• References
• Appel, K.W. Bhave, P.V. Gilliland, A.B.
  Sarwar, G. Roselle, S.J. Evaluation of the
  Community Multiscale Air Quality (CMAQ) Model
  Version 4.5 Sensitivities Impacting Model
  Performance Part II Particulate Matter,
  Atmospheric Environment, 2008, 426057-6066.
• Bhave, P.V. Pouliot, G.A. Zheng, M. Diagnostic
  Model Evaluation for Carbonaceous PM2.5 Using
  Organic Markers Measured in the Southeastern
  U.S., Environmental Science and Technology, 2007,
  411577-1583
• Bhave, P. Yu, S. Lewis, C. Evaluation of a Model
  for Predicting the Fossil-Fuel and Biogenic
  Contributions to Fine Particulate Carbon,
  American Association of Aerosol Research, 11B1,
  Austin, October 2005
• Kleindienst, T.E. Jaoui, M., Lewandowski, M.
  Offenberg, J.H. Lewis, C.W. Bhave, P.V. Edney,
  E.O. Estimates of the Contributions of Biogenic
  and Anthropogenic Hydrocarbons to Secondary
  Organic Aerosol at a Southeastern US Location,
  Atmospheric Environment, 2007, 418288-8300
• Yu, S. Bhave, P.V. Dennis, R.L. Mathur, R.
  Seasonal and Regional Variations of Primary and
  Secondary Organic Aerosols over the Continental
  United States Semi-empirical estimates and model
  evaluation, Environmental Science and Technology,
  2007, 41 4690-4697

• Despite significant updates, CMAQ results still
  fall short of observed SOC in Southeast during
  Summer
• Missing isoprene SOC
• May be due to insufficient in-cloud formation
• Missing aromatic SOC
• May require a VBS approach
• Monoterpene sesquiterpene SOC are in the right
  ballpark
• Preliminary results from Midwest
• All 4 SOC types underestimated from May Sept.
• See poster by Napelenok et al.

19
Extra Figures
20
Site Location Aerial Photo
RTP sampling site located at 35.894ºN and 78.877ºW
21
Site Location Gridded Map w. Counties
MM5 Land Use Categories
Site is in NE corner of grid cell (121,50) 4km
from nearest neighboring cell.
LEGEND Mixed ForestCropland/Woodland
MosaicEvergreen Needleleaf ForestDryland
Cropland and PastureDeciduous Broadleaf Forest