3506B24 Final Report
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- Alkenoic Acids
- Branched Alkanes
- Alkanedioic Acids
- Other Compounds
- Aromatic Carboxylic Acids
- 6 RESULTS Prescribed Burning During the Study Period
- Table 15
Table 14: List of particle-phase organic compounds (POC) quantified via GC/MS.
The target organic species in the derivatized extracts were identified and quantified by GC/MS on a Hewlett-Packard 6890 GC equipped with a Hewlett-Packard 5973 Network mass selective detector (GC/MSD) using a 30 m length x 0.25 mm ID x 0.25 μm film thickness HP-5 MS capillary column. The GC/MS operating conditions were as follows: isothermal hold at 65C for 2 min, temperature ramp of 10 C min-1 to 300 C, and isothermal hold at 300C for 22 min. The interface temperature of GC/MS is 300 C, helium as carrier gas with a flow rate of 1.0 ml min-1, 1 µl split-less injection, scan range 50-500 amu, and electron ionization mode with 70 eV. A set of quantification standards containing more than 100 standard compounds (PMSTD#1-#6) was created by spiking with the deuterated internal standard mix. Each target compound in the present study is quantified by reference to a deuterated internal standard having chemical characteristics and retention time similar to the target compound. The relative response factor (RRF) is calculated from the GC/MS analysis of the quantification standards. For those target compounds which were not found in the quantification standards, identification was achieved by using secondary standards such as candle wax and source samples. The RRF of compounds not present in the quantification standards were estimated from the RRF for compounds having similar chemical structure and retention time. - QA/QC for GC/MS Analysis A robust QA/QC procedure is set for the GC/MS analysis, including the tests of sensitivity, response, and performance of the instrument to the target organic compounds. Details of the QA/QC procedure are listed below: Before running any sample or standards, run standard spectra auto-tune with PFTBA (perfluorotributylamine) to optimize the performance of the instrument and check the potential problems such as air leak; Before running any sample or standards, run un-concentrated composite solvent blanks containing all of the solvent used in the analysis; Run PMSTD #1 1:10 (ten-fold dilution) and PMSTD #4 1:10 (ten-fold dilution) to test the sensitivity of the instrument. The sensitivity check for PMSTD#1 1:10 and PMSTD#4 1:10 includes the following: PMSTD#1 (coronene 300 to pyrene 202 ion ratio): Minimum of 0.25 PMSTD#1 (coronene 300 abundance): Minimum area of 10,000 PMSTD#4 (cholesterol 386 abundance): Minimum area of 1,000,000 At the beginning and the end of each batch of analysis (or minimum of every 3 days), run the following PMSTD standards, which contain the deuterated internal standards #1 and #2: PMSTD#1 1:5 (five-fold dilution); PMSTD#2 1:5; PMSTD#3 1:5 (derivatized with diazomethane before GC/MS analysis); PMSTD#4 1:10; PMSTD#5 1:2; PMSTD#6 1:5 (derivatized with diazomethane before GC/MS analysis). Some secondary standards including picene secondary standard, wood smoke secondary standard, and candle wax secondary standard are run at the end of the sequence to locate those target compounds that cannot be found in the PMSTD standards; The relative response factor (RRF) of each individual target compound to its deuterated internal standard surrogate is calculated and an average for each RRF is obtained from the two PMSTD runs at the beginning and the end of each batch of analysis. These RRF should not shift from historical records more than 50 percent; The target compounds should not be quantified if the signal to noise ratio (peak area) less than 3; After GC/MS injection, the sample and standard vials are sealed immediately with solid caps and Teflon tapes and stored in the freezer to minimize the exposure time at the ambient temperature; Other maintenance for GC/MS: 1) Replace the septum every 50 injections (Bleed/Temp Optimized Inlet septum, part#5183-4757); 2) Replace the liner every batch of sample run or once a month; and 3) Check the ultrapure Helium tank pressure every day to ensure that the pressure is >500 psi. - Other QA/QC All the glassware (e.g., jars, vials, pipettes, filter pipettes, test tubes, beakers, measuring cylinders, adaptors and flasks) and aluminum foil for the use in the analytical procedures (extraction, rotary evaporation, N2 blowing down, methylation, and GC/MS analysis) were baked at 550 ºC for 12 hours. Solvent Blanks. Check the contamination from the solvent used in the sample treatment by concentrating the same amount of solvent used for a sample (~250 ml) then analyzing with GC/MS. All solvent used including hexane, dichloromethane, iso-propanol, and methanol except benzene are optima grade because solvent can be a major contamination source. Benzene is HPLC grade and should be distilled and tested for purity prior to use. Filter or Procedural Blanks. Check the background of the whole procedure by analyzing the pre-baked quartz fiber filters in the same manner as samples before the analysis of ambient samples. 6 RESULTS Prescribed Burning During the Study Period The three largest military installations in Georgia are Forts Stewart, Benning, and Gordon, occupying total land areas of 275,000, 180,000 and 55,000 acres, respectively. Like many other Army lands, the training areas (TAs) of these Georgia installations are relatively undeveloped, yet require intensive land management in order to maintain ecological health and proper functionality for the Army’s specific needs. As mentioned earlier, prescribed burning is the preferred method of choice to manage forested land in the South-Eastern US, for both federally and privately owned lands. Based on a 1997 inventory, of the 24.4 million acres of forested land in Georgia, which is ~66 % of the State’s total land area, 72 % are privately owned, 21 % used in the forest industry, 4 % are otherwise public, and 3 % are national forests [Thompson, 1998]. Per this inventory, and as shown in Figure 24, forest stands classified as pine forest type occupy 14.3 million acres or 58 % of timberland in the State, with loblolly (shortleaf) pine contributing 29 %, longleaf (slash) pine 14 %, and oak-pine 15 %. Other major forest types are oak-hickory with 23 % and oak-gum-cypress with 16 % of the total forested land area. The remaining 3 % are made up by elm-ash-cottonwood, white-red-jack pine, and maple-beech-birch. The USGS forest type map also shows that Fort Benning is situated in an ecological region that is characterized by more mixed forests compared to Fort Gordon, where loblolly pine is the dominant species. The following discussion pertains to Table 15 and appended Table A2, and focuses on the installations’ burn activities during the study period December 2002 to May 2003, and relates those to the burns conducted in the surrounding regions and the rest of Georgia. Note, that the surrounding region of Fort Benning here consists of the counties Chattahoochee, Harris, Marion, Muscogee, Quitman, Schley, Stewart, Talbot and Webster, whereas Richmond, Burke, Columbia, Glascock, Jefferson, Lincoln, McDuffie and Warren are the counties surrounding Fort Gordon. The county level prescribed burn and wild fire data were kindly provided by Mr. Daniel Chan from the Georgia Forestry Commission (GFC). Tables 15 and A2 (more detailed) clearly indicate, that prescribed burns covered several orders of magnitude larger areas than wild fires, at both the two military installations, the surrounding regions and all of Georgia. While April 2003 was the most intense month for prescribed burning at Fort Benning, and January 2003 for Fort Gordon, most areas of the rest of GA were burned in March. Even though not part of the study period, the month of June is listed in the table to illustrate that no prescribed burns (nor wild fires) occurred on the installations, but continued to occur at unaltered levels on privately owned land. It is important to note, that the number of burns/fires that made up for the total areas burned (TAs in case of the military bases) are also listed, indicating much less frequent but larger burns at Fort Gordon, i.e. more emissions per burn, compared to Fort Benning. A reverse relationship, however, can be observed for the regions surrounding each installation, i.e. larger but less frequent burns occurred around Fort Benning compared to the region around Fort Gordon. Even though the total amount of acres burnt in the regions surrounding the installations is similar, the burn intensity, i.e. the size and therefore emissions per burn conducted on the forts is two orders of magnitudes larger. On the other hand, the emissions from the burning of privately owned land in Georgia occur in a regionally distributed manner, bearing important consequences for the assessment of the impacts on regional air quality from the prescribed burning on military installations. 
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