JOSH1 (Joshua Tree, CA, Lat. 34.0694, Long. -116.3888, Alt. 1228)

2 year and 10 month aerosol data are available in Joshua Tree during the sampling period of 1997 - 2002. As shown in Figure 1, the overall average total light extinction coefficient (Bext) is 42.0 Mm-1 (Visual Range ~  93 Km; Deciview ~ 14.4). The average PM2.5 mass concentration is 5.6 mg/m3. The average contributions of the major aerosol components to Joshua Tree haze are particulate sulfate 19.2%, nitrate 24.0%, organic matter (OMC) 13.0%, elemental carbon (light absorbing carbon, LAC) 5.8%, fine soil 2.4% and coarse mass (CM) 11.8%. 

Bext = 42.0 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 62.9 Mm-1, which is about 6.0 times of the value of 10.4 Mm-1 during the 20% best days and 2.2 times of the value of 28.6 Mm-1 during the middle 60% days. Nitrate is the largest contributor to aerosol light extinction during the 20% worst days, and the contribution of nitrate to aerosol light extinction is  ~ 37.5% in worst days. Sulfate and CM also contribute about 21.9% and 15.3% to aerosol light extinction in the 20% worst days. 

Figure 3 suggests that the highest occurrence of the 20% worst days happened in August, in which ~ 53% of the sampling days are the 20% haziest days at Joshua Tree. As shown in Figure 4, sulfate, CM and OMC each contributes ~ 20% to haze in August in the 20% worst days. Nitrate is the largest aerosol contributor to haze except in the summer from June to August, during which sulfate is the largest aerosol contributor.   

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)