CHAS1 (Chassahowitzka NWR, MI, Lat. 28.7484, Long. -82.5549, Alt. 4.3)
Based on the regional haze rule version 2, 3 years of complete aerosol data (2000-2002) are available in Chassahowitzka NWR during the baseline period of 2000 - 2004. The PM2.5 mass and elemental concentrations are missing from March 1 of 2003 to the end of 2004 due to possible problems with the channel A sampler. Therefore, no CM, soil, and sea salt concentrations and extinction coefficients are calculated during this time period, and no complete data are available for 2003 and 2004.
The "Guidance for tracking progress under the regional haze rule" states that "if maximum data recovery is not achieved, EPA believes that a minimum of 3 years of data meeting these completeness requirements is sufficient to calculate the 5-year averages within each 5-year period. This recommendation for at least 3 years out of 5 is consistent with the policy established in EPA’s regulations governing monitoring and analysis of PM2.5, which establishes minimum data requirements for PM2.5 NAAQS comparisons". The discussion below is based on the 3 years of complete data. Efforts have been made to try to estimate the missing concentrations during 2003 and 2004 using the measured concentrations. A separate page is created to discuss the methodology used to substitute the missing numbers and what the 5-year data look like after the substitutions.
As shown in Figure 1, the overall average total light extinction coefficient (Bext) at Chassahowitzka NWR is 84.8 Mm-1 (Visual Range ~ 54 Km; Deciview ~ 21). The average PM2.5 mass concentration is 9.3 mg/m3. The average contributions of the major aerosol components to Chassahowitzka haze are particulate sulfate 55.0%, nitrate 6.5%, organic matter (OMC) 14.2%, elemental carbon (light absorbing carbon, LAC) 5.8%, fine soil 0.9%, sea salt 0.6%, and coarse mass (CM) 4.1%.
Figure 1 Average contributions of major aerosol chemical components to light extinction (Based on data available in 2000-2002)
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 2000-2002)
As Figure 2 indicates, the average light extinction coefficient during the 20% worst days is 139.9 Mm-1, which is about 2.8 times of the value of 49.4 Mm-1 during the 20% best days and 1.8 times of the value of 78.2 Mm-1 during the middle 60% days. Sulfate is the largest aerosol contributor to light extinction during the 20% worst days, with a contribution of ~ 64%. OMC also contributes about 16% to light extinction during the 20% worst visibility days.
Figure 3 suggests that the highest occurrence of the 20% worst days happened in February, in which ~ 32% of the sampling days are the 20% haziest days at Chassahowitzka. As shown in Figure 4, in the 20% worst visibility days, sulfate is the largest aerosol contributor to haze with a contribution from ~50% in the winter to over 70% in the summer. OMC also contributes significantly to light extinction during the 20% worst days especially during the winter time (~25-30% in the winter).
Figure 3 Percentage of sampling days that are 20% worst days in each month (Based on data available in 2000-2002)
Figure 4 Average contributions of major aerosol chemical components to light extinction during 20% worst days in each month (Based on data available in 2000-2002)
