WHPA1 (White Pass, WA, Lat. 46.6243, Long. -121.388, Alt. 1830)
2 year and 9 month aerosol data are available in White Pass during the sampling period of 1997 - 2002. As shown in Figure 1, the overall average total light extinction coefficient (Bext) is 21.9 Mm-1 (Visual Range ~ 178 Km; Deciview ~ 7.8). The average PM2.5 mass concentration is 2.0 mg/m3. The average contributions of the major aerosol components to White Pass haze are particulate sulfate 28.1%, nitrate 6.2%, organic matter (OMC) 11.4%, elemental carbon (light absorbing carbon, LAC) 3.8%, fine soil 1.1% and coarse mass (CM) 3.7%.
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 25.3 Mm-1, which is about 10.9 times of the value of 2.3 Mm-1 during the 20% best days and 2.4 times of the value of 10.5 Mm-1 during the middle 60% days. Sulfate is the largest contributor to aerosol light extinction, with a contribution of 47% in the 20% worst days. OMC also contributes about 26% in the worst days.
Figure 3 suggests that the highest occurrence of the 20% worst days happened in July and August, in which ~ 40% of the sampling days are the 20% haziest days at White Pass. As shown in Figure 4, Sulfate is the largest aerosol contributor to haze during the 20% worst days except February, with a contribution of ~ 30 - 40%. Nitrate is the largest aerosol contributor in February, with a contribution of 31%. OMC contributes ~ 20 - 25% in the 20% worst days during the month of June to October.
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)