Figure 2 Average contributions of major aerosol chemical components to light extinction in 20% best, middle 60% and 20% worst days (Based on data available in 1997-2002)

As Figure 2 indicates, the average aerosol light extinction coefficient (Bext – Rayleigh Scattering (10 Mm^-1)) during the 20% worst days is 22.2 Mm^-1, which is about 6.6 times of the value of 3.3 Mm^-1 during the 20% best days and 2.4 times of the value of 9.2 Mm^-1 during the middle 60% days. OMC and sulfate are the largest contributors to aerosol light extinction, with a contribution of 36% and 28%, respectively in the 20% worst days.

Figure 3 suggests that the highest occurrence of the 20% worst days happened in May, in which ~ 46% of the sampling days are the 20% haziest days at White River National Forest. As shown in Figure 4, OMC is the largest aerosol contributor to haze during the 20% worst days in the summer, with a contribution of ~ 30 - 40%. Sulfate is the largest aerosol contributor to haze for the rest of the year, with a contribution of 20 - 40%. CM and fine soil each contributes ~16% in the 20% worst days in April.

Figure 3 Percentage of sampling days that are 20% worst days in each month (Based on data available in 1997-2002)

Figure 4 Average contributions of major aerosol chemical components to light extinction during 20% worst days in each month (Based on data available in 1997-2002)