6.3 How are Regional Haze Trends Measured?

Regional haze is measured by an extinction coefficient (bext) which represents light

attenuation resulting from scattering and absorption of light from ambient particulate matter plus

scattering of light due to gas molecules in the air (i.e., Rayleigh scattering). Although bext can be

estimated by several different methodologies, the regional haze rule requires that it be estimated

using measured ambient particulate matter. This follows since, for a given set of meteorological

conditions, visibility can be improved by reducing concentrations of ambient particulate matter.

Thus, deriving bext in this manner provides a direct link between regional haze and related

pollutant concentrations. Equation (6.1) may be applied in each Class I area to estimate bext

(Sisler, 1996, IMPROVE, 2000). The equation reflects empirical relationships derived between

measured mass of particulate matter components and transmissometer measurements of bext at

monitoring sites in Class I areas within the IMPROVE network.

bext = 3(f(rh))[SO4] + 3(f(rh))[NO3] + 4(f’(rh))[OC] + 10[EC] + 1[Fine

Soil] + 0.6[CM] + brayleigh (6.1)

where

the numerical coefficients on the right hand side of the equation represent the light scattering or

absorption efficiency, m2/gm of the corresponding component of particulate matter,

n701 - n702 - n703 - n704 - n705 - n706 - n707 - n707 - n709 - n710 - n711 - n712 - n713 - n714 - n715 - n716 - n717 - n718 - n719 - n720 - n721 - n722 - n723 - n724 - n725 - n726 - n727 - n728 - n729 - n730 - n731 - n732 - n733 - n734 - n735 - n736 - n737 - n738 - n739 - n740 - n741 - n742 - n743 - n744 - n745 - n746 - n747 - n748 - n749 - n750

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