Review of the IMPROVE Equation for Estimating Ambient Light Extinction
Coefficients - Final Report

Jenny L. Hand and William C. Malm

March 2006

Abstract -  The Interagency Monitoring of Protected Visual Environments
(IMPROVE) protocols for reconstructing ambient light extinction from
measured aerosol species is the basis for evaluating compliance under
the Regional Haze Rule. We review the assumptions involved in computing
reconstructed light extinction using the IMPROVE protocol. This review
includes examining the biases in the measurements of aerosol
composition, the assumed chemical forms of aerosol species, particle
hygroscopicity, and assumed mass scattering efficiencies. We present a
thorough survey of estimates of mass scattering efficiencies from recent
peer-reviewed literature. Furthermore, we use IMPROVE nephelometry and
composition data to estimate mass scattering efficiencies using a
variety of methods. The current mass scattering efficiencies applied in
the IMPROVE equation are then interpreted in the context of this survey
and results derived from the IMPROVE data analyses. Finally, a summary
of provisional recommendations for refinements to the IMPROVE equation
and a discussion of important uncertainties to consider in the
assumptions is presented. Although tentative recommendations of
refinements to the IMPROVE equation are presented, final refinements to
the IMPROVE equation await future discussions of the results presented
here.

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