SNPA1 (Snoqualamie Pass, Snoqualamie N.F, WA, Lat. 47.4203, Long. -121.4277, Alt. 1160)
5 and a half years aerosol data are available in Snoqualamie Pass, Snoqualamie N.F during the sampling period of 1997 - 2002. As shown in Figure 1, the overall average total light extinction coefficient (Bext) is 36.8 Mm-1 (Visual Range ~ 106 Km; Deciview ~ 13.0). The average PM2.5 mass concentration is 3.7 mg/m3. The average contributions of the major aerosol components to Snoqualamie Pass, Snoqualamie N.F haze are particulate sulfate 33.3%, nitrate 13.9%, organic matter (OMC) 14.8%, elemental carbon (light absorbing carbon, LAC) 7.1%, fine soil 0.8% and coarse mass (CM) 2.8%.
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 52.6 Mm-1, which is about 6.3 times of the value of 8.3 Mm-1 during the 20% best days and 2.2 times of the value of 23.9 Mm-1 during the middle 60% days. Sulfate is the largest contributor to aerosol light extinction, with a contribution of 43% in the 20% worst days.
Figure 3 suggests that the highest occurrence of the 20% worst days happened in July and August, in which ~ 40 - 50% of the sampling days are the 20% haziest days at Snoqualamie Pass, Snoqualamie N.F. As shown in Figure 4, sulfate is the largest aerosol contributor to haze during the 20% worst days the whole year except January, February, November and December, with a contribution of 32 - 45% during the 20% worst days. Nitrate is the largest aerosol contributor to haze in the 20% worst days in January, February, November 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)