BALD1 (Mount Baldy, AZ, Lat. 34.0584, Long. -109.4405, Alt. 2513)
2 and a half years aerosol data are available in Mount Baldy during the sampling period of 1997 - 2002. As shown in Figure 1, the overall average total light extinction coefficient (Bext) is 24.3 Mm-1 (Visual Range ~ 161 Km; Deciview ~ 8.9). The average PM2.5 mass concentration is 3.4 mg/m3. The average contributions of the major aerosol components to Mount Baldy haze are particulate sulfate 19.7%, nitrate 3.8%, organic matter (OMC) 18.4%, elemental carbon (light absorbing carbon, LAC) 6.3%, fine soil 3.1% and coarse mass (CM) 7.4%.
Figure 1 Average contributions of major aerosol chemical components to light extinction (1997-2002)
Figure 2 Average contributions of major aerosol chemical components to light extinction in 20% best, middle 60% and 20% worst days (1997-2002)
As Figure 2 indicates, the average aerosol light extinction coefficient (Bext – Rayleigh Scattering (10 Mm-1)) during the 20% worst days is 28.8 Mm-1, which is about 5.3 times of the value of 5.4 Mm-1 during the 20% best days and 2.3 times of the value of 12.3 Mm-1 during the middle 60% days. Organic matter is the largest contributor to aerosol light extinction during the 20% worst days, and the contribution of OMC to aerosol light extinction is ~ 42.3% in worst days. LAC is also responsible for 12.5% of the aerosol light extinction in the 20% worst days.
Figure 3 suggests that the highest occurrence of the 20% worst days happened in the summer from July to September, in which ~40% of the sampling days are the 20% haziest days at Mount Baldy. As shown in Figure 4, in the summer, OMC and sulfate dominate the aerosol light extinction, and both contribute about 30% - 40% to haze during the 20% worst days. One big peak happened in June with very high OMC and LAC concentrations, which may due to special pollution events such as forest fires.
Figure 3 Percentage of sampling days that are 20% worst days in each month (1997-2002)
Figure 4 Average contributions of major aerosol chemical components to light extinction during 20% worst days in each month (1997-2002)