WICA1 (Wind Cave, SD, Lat. 43.5576, Long. -103.4838, Alt. 1300)

3 years aerosol data are available in Wind Cave during the sampling period of 1997 - 2002. As shown in Figure 1, the overall average total light extinction coefficient (Bext) is 30.1Mm-1 (Visual Range ~ 130 Km; Deciview ~ 11). The average PM2.5 mass concentration is 3.5 mg/m3. The average contributions of the major aerosol components to Wind Cave haze are particulate sulfate 26.7%, nitrate 9.4%, organic matter (OMC) 16.0%, elemental carbon (light absorbing carbon, LAC) 5.1%, fine soil 1.8% and coarse mass (CM) 7.7%. 

Bext = 30.1 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 40.9 Mm-1, which is about 5.2 times of the value of 7.8 Mm-1 during the 20% best days and 2.4 times of the value of 17.0 Mm-1 during the middle 60% days. Sulfate and OMC are the largest contributors to aerosol light extinction, with a contribution of 37% and 27%, respectively in the 20% worst days.

Figure 3 suggests that the highest occurrence of the 20% worst days happened in July, in which ~ 45% of the sampling days are the 20% haziest days at Wind Cave. As shown in Figure 4, OMC is the largest aerosol contributor to haze during the 20% worst days in the summer, with a contribution of ~ 35 - 40%. Sulfate is the largest aerosol contributor to haze for the rest of the year, with a contribution of 30 - 55%. Nitrate also contributes ~30% in the 20% worst days in the winter.

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)