6.3 How are Regional Haze Trends Measured?
Regional haze is measured by anextinction 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)
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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