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 46.8 Mm^-1, which is about 2.9 times of the value of 16.3 Mm^-1 during the 20% best days and 1.8 times of the value of 25.9 Mm^-1 during the middle 60% days. CM and sulfate are two of the largest contributors to aerosol light extinction, with a contribution of 26% and 21% in the 20% worst days. Nitrate also contributes about 18% to the aerosol light extinction.

Figure 3 suggests that the highest occurrence of the 20% worst days happened in August, in which ~ 60% of the sampling days are the 20% haziest days at Saguaro West. As shown in Figure 4, Sulfate is the largest aerosol contributor to haze in August, with a contribution of ~ 30%. CM is the two largest aerosol contributor to haze in the 20% worst days most of the year, except January, August and September when sulfate is the largest aerosol contributor, as well as December when nitrate is the largest one. 

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)