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 19.9 Mm^-1, which is about 8.6 times of the value of 2.3 Mm^-1 during the 20% best days and 2.8 times of the value of 7.0 Mm^-1 during the middle 60% days. Sulfate and OMC are two of the largest contributors to aerosol light extinction, with a contribution of 43% and 32% in the 20% worst days.

Figure 3 suggests that the highest occurrence of the 20% worst days happened in April, in which ~ 63% of the sampling days are the 20% haziest days at Trapper Creek. As shown in Figure 4, sulfate is the largest aerosol contributor to haze during the 20% worst days in April, with a contribution of 39% during the 20% worst days. OMC is the largest aerosol contributor in June, August and September, while nitrate is the largest one in October. Sulfate is the largest aerosol contributor to haze in the 20% worst days for the rest of 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)