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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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Volume 8, issue 6
Geosci. Model Dev., 8, 1763–1773, 2015
https://doi.org/10.5194/gmd-8-1763-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Geosci. Model Dev., 8, 1763–1773, 2015
https://doi.org/10.5194/gmd-8-1763-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Methods for assessment of models 12 Jun 2015

Methods for assessment of models | 12 Jun 2015

Path-integral method for the source apportionment of photochemical pollutants

A. M. Dunker A. M. Dunker
  • LLC, Bloomfield Hills, Michigan, USA

Abstract. A new, path-integral method is presented for apportioning the concentrations of pollutants predicted by a photochemical model to emissions from different sources. A novel feature of the method is that it can apportion the difference in a species concentration between two simulations. For example, the anthropogenic ozone increment, which is the difference between a simulation with all emissions present and another simulation with only the background (e.g., biogenic) emissions included, can be allocated to the anthropogenic emission sources. The method is based on an existing, exact mathematical equation. This equation is applied to relate the concentration difference between simulations to line or path integrals of first-order sensitivity coefficients. The sensitivities describe the effects of changing the emissions and are accurately calculated by the decoupled direct method. The path represents a continuous variation of emissions between the two simulations, and each path can be viewed as a separate emission-control strategy. The method does not require auxiliary assumptions, e.g., whether ozone formation is limited by the availability of volatile organic compounds (VOCs) or nitrogen oxides (NOx), and can be used for all the species predicted by the model. A simplified configuration of the Comprehensive Air Quality Model with Extensions (CAMx) is used to evaluate the accuracy of different numerical integration procedures and the dependence of the source contributions on the path. A Gauss–Legendre formula using three or four points along the path gives good accuracy for apportioning the anthropogenic increments of ozone, nitrogen dioxide, formaldehyde, and nitric acid. Source contributions to these increments were obtained for paths representing proportional control of all anthropogenic emissions together, control of NOx emissions before VOC emissions, and control of VOC emissions before NOx emissions. There are similarities in the source contributions from the three paths but also differences due to the different chemical regimes resulting from the emission-control strategies.

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A new method is presented for allocating the anthropogenic part of a pollutant concentration to the sources responsible. The method requires integrating sensitivity coefficients over a range of emissions defined by an emission-control strategy. A simplified photochemical model is used to evaluate options for the numerical integration and the dependence of the source contributions on the control strategy. Results are presented for ozone, formaldehyde, nitrogen dioxide, and nitric acid.
A new method is presented for allocating the anthropogenic part of a pollutant concentration to...
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