1. M. Samaali, M. Sassi, V. Bouchet
Application of an emissions source apportionment method for primary PM components in a regional air quality model
M. Samaali, M. Sassi, V. Bouchet
Environment Canada, Meteorological Service of Canada, Air Quality Modelling Application Section, 2121 Trans-Canada highway, Dorval, Québec, H9P 1J3.
M. Moran
Air Quality Research Division, Science and Technology Branch, Environment
Canada, 4905 Dufferin Street, Toronto, ON, M3H 5T4, Canada. Environment
6-8th Oct. 2008, Chapel Hill, NC

2. Contents Introduction
Implementation of a source apportionment (tagged species) method in AURAMS
Emissions inventory analysis
Modeling results (method’s verification and application)
Conclusion and future work

3. Introduction
- How much does a given source contribute to total PM pollution?
Two main categories of source apportionment methods used in Eulerian 3D AQ model (Yarwood et al., 2004):
(1) sensitivity analysis methods
(2) tagged species methods.
- American AQ models (e.g. CMAQ, CAMx) use already both techniques.
- Canadian AQ models (e.g. AURAMS, CHRONOS) used only for scenarios analysis so far.
Objective: implement, verify and apply a tagged species method in AURAMS to tag and track primary organic (POC) & elemental carbons (EC) emissions from 4 sources in the North American domain.

4. AQ model description (A Unified Regional Air quality Modeling System: AURAMS)
Characteristic
Description
Meteorological driver
GEM (offline)
Anthropogenic emissions
Processed by SMOKE (spatial and temporal )
PM emissions
2 inputs fields (PMf and PMc) speciated to 8 species and size disaggregated to 12 bins.
PM size distribution representation
Sectional method (12 bins)
Lateral boundary conditions
no-gradient, time independent/dependent
Aerosol physics
Nucleation, condensation/evaporation, coagulation, aerosol-cloud interactions, hygroscopic growth, etc.
Dry deposition
Resistance-based method (Zhang et al., 2001, 2002)
Wet deposition
Scavenging and removal of PM and soluble gases.

5. Implementation of a tagged species method in AURAMS
4 source types (area and point):
on-road (vehicles, trucks, motorcycles),
off-road & others (marine, air, rail, residential, construction, agriculture, etc.),
minor points (stack height < 35m)
major points (stack height >= 35m)
2 tracers (i.e. POC and EC) for each source with 12 bins each: species increase from 108 to 204 PM species.
Apply the same physical and chemical processes treatment to the tagged species as the original POC and EC species:
Transport (3D advection) and vertical diffusion
Removal processes (dry deposition, wet deposition and rain, fog, and cloud processing)
Emissions (chemical speciation)

6. Emissions inventory analysis (1): POC and EC emissions totals (Jun-Jul-Aug 2002)
Monthly total POC (PM2.5 ) emissions by source type
Monthly total EC (PM2.5 ) emissions by source type
Off-road & other sources are major emitter of POC
On-road sources are major emitter of EC

7. Emissions inventory analysis (2) : POC from on-road and off-road & other sources (June 2002)
Total POC (PM2.5 ) from on-road
Total POC (PM2.5 ) from off-road & other.
- Most of the emissions are located in the Eastern domain
- Canadian cities are surrounded by high emission levels

8. Emissions inventory analysis (3): POC from minor and major points (June 2002)
Total POC (PM2.5 ) emissions from minor points
Total POC (PM2.5 ) emissions from major points
- Highest spatial density for minor points
- Highest emission levels for major points

9. Runs settings and CPU time analysis
Run period (J-J-A 2002) : started in May. 25th 2002, at 6:00
Lateral boundary (LB) & initial conditions: zero initial conditions & zero-gradient method for LB conditions
Required computational resources on Environment Canada IBM cluster:
1 day (24 h)
3 months (2208 h)
Default AURAMS
2h40min
254h20min
(~ 10.2 days)
AURAMS with 8 extra PM tracers (i.e. 96 species)
4h20min
398h40min
(~16.6 days)
~ 62% CPU time increase
Optimization of the code to keep CPU time increase at minimum

10. Modeling results (tagging method verification) (1)
Average difference: ug/m3 (1.48%)
Average difference: ug/m3 (0.37%)
Good agreement between total POC and EC and their respective tracers sums

11. Modeling results (tagging method verification) (2)
POC concentrations contributions
POC emissions contributions
There is a correspondence between concentration and emission
contributions for each POC tagged species

12. Modeling results (tagging method verification) (3)
EC concentrations contributions
EC emissions contributions
There is a correspondence between concentration and emission
contributions for each EC tagged species

13. Modeling results (tagging method application) (4)
Off-road & other.
On-road 3% 5% 6% 2% 6% 3% 4%
On-road POC concentration decrease: dispersion by wind & no significant
surrounding emission sources.
Off-road & other. POC concentration increase: balance with on-road & POC
transport from surrounding sources.

14. Conclusion and future work
The tagged species method implemented in AURAMS verifies well the mass conservation and hypotheses (linearity) of primary chemistry processes.
The method’s application is promising for:
(1) Detailed analysis of pollution in Canadian cities
(2) Assessment studies of specific sources (e.g. transportation)
- Code optimization is underway for possible future long-term (annual) runs.