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 34.4 Mm^-1, which is about 3.2 times of the value of 10.8 Mm^-1 during the 20% best days and 1.7 times of the value of 19.7 Mm^-1 during the middle 60% days. OMC and Sulfate are two of the largest contributors to aerosol light extinction, with a contribution of 28% and 27% in the 20% worst days. CM also contributes about 21% to aerosol light extinction in the 20% worst days.

Figure 3 suggests that the highest occurrence of the 20% worst days happened in November, in which ~ 40% of the sampling days are the 20% haziest days at Tonto National Monument. As shown in Figure 4, OMC is the largest aerosol contributor to haze during the 20% worst days in November, with a contribution of 31% during the 20% worst days. Sulfate, OMC and CM are all important haze contributors throughout the year, each with a contribution of ~ 10 - 30% in the 20% worst days. Nitrate also contributes ~ 20% in January and December. 

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)