Center for Environmental Research and Technology/Air Quality Modeling University of California at Riverside CMAQ Tagged Species Source Apportionment (TSSA) Gail Tonnesen, Bo Wang et al., Air Quality Modeling Group University of California, Riverside WRAP Attribution of Haze Meeting, Denver, CO July 22, 2004
CMAQ Tagged Species Source Apportionment (TSSA). Gail Tonnesen, Bo Wang et al., Air Quality Modeling Group University of California, Riverside WRAP Attribution of Haze Meeting, Denver, CO July 22, 2004. Need to understand which emissions sources contribute to haze and other pollutants. - PowerPoint PPT Presentation
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Center for Environmental Research and Technology/Air Quality Modeling
University of California at Riverside
CMAQ Tagged Species Source Apportionment (TSSA)
Gail Tonnesen, Bo Wang et al.,
Air Quality Modeling Group
University of California, Riverside
WRAP Attribution of Haze Meeting, Denver, CO July 22, 2004
Center for Environmental Research and Technology/Air Quality Modeling
University of California at Riverside
Motivation
• Need to understand which emissions sources contribute to haze and other pollutants.
• Use this information to assist in developing control strategies.
Center for Environmental Research and Technology/Air Quality Modeling
University of California at Riverside
Modeling Approaches for Source Apportionment
• Chemical Mass Balance analysis
• Back-trajectory models
• Lagrangian models
• Sensitivity Studies
• Mass tracking approaches.
Center for Environmental Research and Technology/Air Quality Modeling
University of California at Riverside
Sensitivity Methods (1)
1. Run a model Base Case simulation.
2. Add-in or Zero-out a particular source and run a the model again.
3. The difference in the base case and the sensitivity case predicts the effect of changing that source on concentration at all receptor sites.
Center for Environmental Research and Technology/Air Quality Modeling
University of California at Riverside
Sensitivity Methods (2)
• Advantages of Sensitivity Methods:– directly related to development of control measures.– Conceptually simple to apply.
• Problems with Sensitivity Methods:– Brute force approaches (removing one species in each
model run) are computationally expensive.– Sensitivity results depend on the base case scenario.– Sensitivities results can be non-linear and non-additive.– CMAQ exhibits numerical noise in PM sensitivity runs.
Center for Environmental Research and Technology/Air Quality Modeling
University of California at Riverside
Sensitivity Methods (3)
• Decoupled Direct Method is a computationally efficient sensitivity method:– Calculates many sensitivities in one run.– Difficult to implement in PM models.– Calculates derivative – but sensitivities can be
non-linear.
• Recommendation: Sensitivity studies are a valuable tool, but expensive to apply, and care is needed in interpretation of results.
Center for Environmental Research and Technology/Air Quality Modeling
University of California at Riverside
Mass Tracking Methods
• Mass Tracking Algorithms– Output and analyze mass flux terms and
chemical reaction rates for each grid cell.– Computationally prohibitive.
• OSAT– Uses tracers to track O3 formation that was
sensitive to VOC or NOx.
Center for Environmental Research and Technology/Air Quality Modeling
University of California at Riverside
Tagged Species Approach (1)
• Use “Tagged Species” or Tracers to track chemical transformations and transport of each PM species or PM precursor .
• Add the tracers for key species and for defined source regions & source categories.
• Provides 3-D fields showing source attribution of of PM species for any grid cell in model domain.
Center for Environmental Research and Technology/Air Quality Modeling
University of California at Riverside
Tagged Species Approach (2)
• Method: Add one new set of tagged species for each emissions source category or source location being tracked.– Straight forward for non-reactive species: add 1 tracer
for each source.– Example: in each grid cell the sum of all tracers for EC
equals the total (bulk) EC concentration in each cell.– Each tracer is defined for all grid cells and is emitted,
transported, and removed proportional to its weight of the bulk species in each grid cell.
Center for Environmental Research and Technology/Air Quality Modeling
University of California at Riverside
Tagged Species Approach (3)
• More complicated for chemical reactive species and secondary particulates:– Must also track the chemical reactions that convert a
tracer between different gas species and from gas to PM.– Model include approximately 6 forms of N species, must
carry 6 additional tracers for each NOx source category to track the contributions to aerosol nitrate.
– SOA formation is still more complex, not included in current algorithm.
– SO4 and other PM species are easier and less computational expensive to treat.
Center for Environmental Research and Technology/Air Quality Modeling