SAGU1 (Saguaro National Monument, AZ, 32.1742, Long. -110.7372, Alt.933)        

1 year and 9 month aerosol data are available in Saguaro National Monument during the sampling period of 1997 - 2002. As shown in Figure 1, the overall average total light extinction coefficient (Bext) is 31.5 Mm-1 (Visual Range ~ 124 Km; Deciview ~ 11.5). The average PM2.5 mass concentration is 6.3 mg/m3. The average contributions of the major aerosol components to Saguaro National Monument haze are particulate sulfate 19.9%, nitrate 7.7%, organic matter (OMC) 13.0%, elemental carbon (light absorbing carbon, LAC) 6.6%, fine soil 8.7% and coarse mass (CM) 12.4%. 

Bext = 31.5 Mm-1

Figure 1 Average contributions of major aerosol chemical components to light extinction (Based on data available in 1997-2002)

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 35.5 Mm-1, which is about 2.8 times of the value of 12.6 Mm-1 during the 20% best days and 1.8 times of the value of 19.7 Mm-1 during the middle 60% days. Sulfate is the largest contributor to aerosol light extinction, with a contribution of 23% in the 20% worst days. CM, OMC and nitrate each contributes about 18% to aerosol light extinction in the 20% worst days. 

Figure 3 suggests that the highest occurrence of the 20% worst days happened in December, in which ~50% of the sampling days are the 20% haziest days at Saguaro National Monument.  As shown in Figure 4, in December, particulate nitrate is the largest aerosol contributor to haze, with a contribution of ~ 37% during the 20% worst days. The largest aerosol contributor to haze is OMC in May and June, sulfate in July to September and November, CM in February, April and October, and Nitrate 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)