SAMA1 (St. Marks NWR, FL, Lat. 30.0926, Long. -84.1614, Alt. 7.75)
IMPROVE sampling started on 9/31/2000 at St. Marks NWR. Therefore, no complete aerosol data is available in 2000. During the year of 2001, there are no valid measurements (i.e. concentrations of all major aerosol chemical components are missing) in 39 sampling days (out of a total of 122 sampling days). Moreover, there are consecutive missing sampling days (again, no concentration is available for any major aerosol component) from April 13 to May 28, and from July 24 to September 14. Therefore, data from 2001 also can not be used based on the regional haze rule. In 2004, OC/EC concentrations are missing from June 29 to November 23 (due to possible problems with the channel C sampler), although concentrations of the other major components are available most of the time during this period. Based on the regional haze rule version 2, only 2 years of complete aerosol data (2002-2003) are available in St. Marks during the baseline period of 2000-2004. 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". Because only OC/EC concentrations are missing in 2004, we tried to estimate the missing OC/EC concentrations using the measured concentrations of other components such as hydrogen (H) and Sulfur (S). Based on the data in 2002 and 2003, a nice correlation has been found between the so-called organic hydrogen (H-1/4*S) and measured OC as shown in Figure 1. Therefore, the missing OC concentrations in 2004 may be estimated as 9.7 times organic H concentrations based on measured H and S concentrations during these days (OC is set to be zero if the calculated organic H is negative). Figure 2 suggests that the EC to OC ratio is about 0.18 during 2002 and 2003. So, the missing EC concentrations in 2004 can be estimated as 0.18 times calculated OC concentrations.
Figure 1 Relationship between organic H and measured OC in 2002 and 2003
Figure 2 Relationship between measured OC and EC in 2002 and 2003
After substituting the missing OC/EC data in 2004 using the methodology described above, 3 years of complete aerosol data (2002-2004) are available in St. Marks NWR during the baseline period of 2000 - 2004. As shown in Figure 3, the overall average total light extinction coefficient (Bext) at St. Marks NWR is 82.4 Mm-1 (Visual Range ~ 58 Km; Deciview ~ 20). The average PM2.5 mass concentration is 9.2 mg/m3. The average contributions of the major aerosol components to St. Marks haze are particulate sulfate 58.7%, nitrate 4.7%, organic matter (OMC) 14.5%, elemental carbon (light absorbing carbon, LAC) 4.2%, fine soil 0.8%, sea salt 0.7%, and coarse mass (CM) 3.0%.
Figure 3 Average contributions of major aerosol chemical components to light extinction (Based on data available in 2002-2004)
Figure 4 Average contributions of major aerosol chemical components to light extinction in 20% best, middle 60% and 20% worst days (Based on data available in 2002-2004)
As Figure 4 indicates, the average light extinction coefficient during the 20% worst days is 144.4 Mm-1, which is about 3.5 times of the value of 41.3 Mm-1 during the 20% best days and 1.9 times of the value of 74.6 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 ~ 65%. OMC also contributes about 18% to light extinction during the 20% worst visibility days.
Figure 5 suggests that the highest occurrence of the 20% worst days happened in October, in which ~ 38% of the sampling days are the 20% haziest days at St. Marks. As shown in Figure 6, in the 20% worst visibility days, sulfate is the largest aerosol contributor to haze with a contribution of ~40% in the winter to ~80% in the summer and fall. OMC also contributes about 30% in the winter and spring (January to May) during the 20% worst days.
Figure 5 Percentage of sampling days that are 20% worst days in each month (Based on data available in 2002-2004)
Figure 6 Average contributions of major aerosol chemical components to light extinction during 20% worst days in each month (Based on data available in 2002-2004)
