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 38.6 Mm^-1, which is about 10.4 times of the value of 3.7 Mm^-1 during the 20% best days and 2.5 times of the value of 15.6 Mm^-1 during the middle 60% days. Sulfate and OMC are two of the largest contributors to aerosol light extinction, with a contribution of 38% and 35% in the 20% worst days.

Figure 3 suggests that the highest occurrence of the 20% worst days happened in August, in which ~ 55% of the sampling days are the 20% haziest days at Three Sisters Wilderness. As shown in Figure 4, Sulfate and OMC are the largest aerosol contributors to haze during the 20% worst days in August, with a contribution of 30% and 28% during the 20% worst days. Both sulfate and OMC are important haze contributors throughout the year.

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)