ACCURACY OF REGIONAL OZONE AND PM BACKGROUND

Project No. A-65

Leaders:         A. M. Dunker
                        R. S. MacArthur

Scope and Objective

The objective of this project is to determine whether the anthropogenic increment contribution to O3 and PM is correctly predicted in regional simulations, and, if not, what the implications are for control strategies.  This objective includes determining whether the emission inventories for natural sources yield O3 and PM concentrations in reasonable agreement with accepted background concentration ranges and if agreement is not reasonable, determine possible deficiencies in the natural emission inventories and the potential impacts on O3 and PM control strategies.

Current Status and Future Program

Regional simulations of O3 and PM employ emission inventories for natural and anthropogenic sources.  The anthropogenic increment contribution to O3 and PM is simply the difference between a simulation with all sources present and a simulation with only natural sources present.  Emission control strategies seek to reduce the anthropogenic emissions so that the background O3 or PM plus the anthropogenic increment to the pollutant meets the relevant standard.

The accuracy of regional simulations of O3 and PM has been determined by comparing model predictions for historical episodes or entire years to ambient data.  However, there have apparently been no tests reported in the literature on whether regional simulations using only natural emissions give O3 and PM concentrations in reasonable agreement with estimates of background O3 and PM concentrations.  In particular, regional simulations normally use “clean” boundary concentrations, but it is unclear whether simulations with natural emissions alone will give O3 and PM concentrations consistent with these “clean” boundary concentrations. 

If regional simulations with natural emissions give O3 and PM concentrations that are too low or too high compared to background concentrations but simulations with all emissions included agree with measurements, then the anthropogenic increments of O3 and PM will be too high or too low, respectively.  If the anthropogenic increments of O3 and PM are inaccurate, then emission control strategies developed from regional modeling (particularly NOx control strategies) are also likely to be inaccurate. 

The approach for this project calls for the contractor to acquire the meteorological, emissions, and other data for several regional simulations of O3 and PM conducted over the past 10 years.  The simulations can be for annual-average or episodic concentrations.  However, the emissions for natural sources must be available separately or can be readily determined separately from the emissions for anthropogenic sources.  The contractor will then run simulations with only the natural emissions and compare results to the boundary concentrations used in the simulations and to literature values for background O3 and PM concentrations.  If there is disagreement between the simulations and the boundary or background concentrations, the contractor will conduct sensitivity simulations to estimate possible deficiencies in the natural emissions or other model input data.  The contractor will conduct additional sensitivity simulations to estimate how the deficiencies affect control strategies developed from the regional modeling.  Deliverables for the project will include quarterly reports and a final report.  The final report will include a draft paper for submission to a journal.  The final report will recommend modifications to model input data and/or additional research if the simulations of background O3 and PM appear inadequate. 

A request for proposal was issued and the committee selected ENVIRON to conduct this study with a start date of November 2007.  The committee received the literature review and the contractor-recommended modeling approach in March 2008 and both were approved.  The project is scheduled for completion in 2008. 

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