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 25.8 Mm^-1, which is about 5.2 times of the value of 4.9 Mm^-1 during the 20% best days and 2.3 times of the value of 11.5 Mm^-1 during the middle 60% days. OMC is the largest contributor to aerosol light extinction, with a contribution of 47% in the 20% worst days.

Figure 3 suggests that the highest occurrence of the 20% worst days happened in August, in which ~ 42% of the sampling days are the 20% haziest days at Yellowstone National Park. As shown in Figure 4, OMC is the largest aerosol contributor to haze during the 20% worst days in the summer and September and October, with a contribution of ~ 20 - 50%. Sulfate and Nitrate each contributes ~30% in the 20% worst days in the winter. Sulfate is the largest aerosol contributor to haze during the 20% worst days in the Spring, with a contribution of ~ 20 - 25%.

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)