SWAN1 (Swanquarter NWR, NC, Lat. 35.451, Long. -76.2075, Alt. -3.7) Print-Friendly Version Print-Friendly Version (B&W)
IMPROVE sampling started on 6/10/2000 at Swanquarter NWR. Therefore, no complete aerosol data is avaliable in 2000. The PM2.5 mass and elemental concentrations are missing from August 22 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 available during this time period. Based on the regional haze rule version 2, only 2 years of complete aerosol data (2001-2002) are available in Swanquarter NWR 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". In order to meet the data recovery requirement (i.e. at least 3 years of complete data during 2000-2004), the methodology discussed below is used to to estimate the missing concentrations in 2003 and 2004, and the numbers shown on this page are based on 4 years of aerosol data (2001-2004) during the baseline period of 2000 - 2004 after all possible substitutions.
PM2.5 sea salt concentration is estimated as the concentration of chloride ion (Cl-) measured by ion chromatography multiplied by 1.8. If the chloride measurement is below the detection limit, missing or invalid, and the concentration of chlorine (Cl) measured by XRF is above the detection limit, then the PM2.5 sea salt concentration is estimated as the concentration of chlorine (Cl) measured by XRF multiplied by 1.8. If both chloride and chlorine are missing or invalid, PM2.5 sea salt concentration is not available. Otherwise, PM2.5 sea salt concentration is set to be zero.
A fairly good correlation has been found between PM2.5 and PM10 based on the measurements in 2001-2002 as shown in the figure below. For 2003 and 2004 when PM2.5 mass is missing, PM2.5 is estimated as PM10/1.5, and coarse mass (CM) concentration is then calculated as PM10 - PM2.5.
Figure 1 Relationship between measured PM10 and PM2.5 in 2001-2002
Fine soil concentration = PM2.5 – [Ammonium Sulfate] – [Ammonium Nitrate] – [OMC] – [EC] – [Sea Salt]. If the calculated fine soil is less than zero, it is set to be zero.
As shown in Figure 2, the overall average total light extinction coefficient (Bext) is 68.4 Mm-1 (Visual Range ~ 72 Km; Deciview ~ 18). The average PM2.5 mass concentration is 8.0 mg/m3. The average contributions of the major aerosol components to Seney haze are particulate sulfate 56.2%, nitrate 6.1%, organic matter (OMC) 10.0%, elemental carbon (light absorbing carbon, LAC) 3.2%, fine soil 1.4%, sea salt 1.1%, and coarse mass (CM) 4.4%.
Figure 2 Average contributions of major aerosol chemical components to light extinction (Based on data available in 2001-2004) (B&W)
Figure 3 Average contributions of major aerosol chemical components to light extinction in 20% best, middle 60% and 20% worst days (Based on data available in 2001-2004) (Data Table) (B&W)
As Figure 3 indicates, the average light extinction coefficient during the 20% worst days is 116.1 Mm-1, which is about 5.4 times of the value of 21.6 Mm-1 during the 20% best days and 2.4 times of the value of 47.9 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 ~ 68%.
Figure 4 suggests that the highest occurrence of the 20% worst days happened in July, in which ~54% of the sampling days are the 20% haziest days at Swanquarter. As shown in Figure 5, in the 20% worst visibility days, sulfate is the largest aerosol contributor to haze with a contribution from ~40% in the winter to over 70% in the summer and early fall.
Figure 4 Percentage of sampling days that are 20% worst days in each month (Based on data available in 2001-2004) (Data Table) (B&W)
Figure 5 Average contributions of major aerosol chemical components to light extinction during 20% worst days in each month (Based on data available in 2001-2004) (Data Table) (B&W)
List of Tables:
1. Number of measurements available in each month during 2001-2004
4. Percentage of worst days happened in each month based on data available during 2001-2004
