3506B24 Final Report
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Figure 37: Comparison of average CO and OH free tropospheric background levels in the Northern Hemisphere; adapted from Novelli et al. [1998]. The background levels determined from the CO/NOy regression analysis presented above, correspond well with what is considered to be representative for the free troposphere of the Northern Hemisphere, i.e. at least for the period between December and March, when [CO] steadily increased from ~150 ppbv to a maximum of ~200 ppbv. However, while the remote measurements between 19991 and ‘94 show a steep decline between April and June, the CO concentrations representing background levels of Georgia and perhaps the entire SE US remain elevated during the same period in 2003. This can be caused by i) elevated CO emissions (here e.g. from prescribed burning); or ii) less effective removal by reduced OH abundance. Note that the possibility of lower OH abundance in 2003 compared to earlier years (here 1991-94) may be less realistic, as stratospheric [O3] is just now considered to be at an all-time minimum, and thus UV intensity – the immediate precursor for OH - is peaking. Therefore, the observed elevated CO background levels must be a result of increased emissions. While the evidence gathered above is compelling, it is still unclear to what extent this elevated CO background is caused by all the prescribed burning conducted region-wide. A complete, detailed inventory of all prescribed burning activities in the entire southeastern U.S. is required to investigate this source’s impact on CO background levels in particular and regional air quality in general. In a continuation project of this Study, Georgia Tech has begun to develop such an inventory and to integrate it into emissions based air quality modeling, in order to i) better understand the prescribed burning emissions’ importance for regional air quality relative to other sources; ii) improve and validate air quality models from local to regional scales; and iii) develop land management strategies that help minimize the impacts on local to regional air quality. 6.5.3 Influences on State Regulatory PM2.5 Monitoring Based on EPA’s recent emissions trends [US EPA, 2003], the main sources for primary PM2.5, i.e. fine PM that is being emitted directly into the atmosphere, are fugitive dust (36%), stationary fuel combustion (18%), other combustion (13%), industrial processes (14%), agriculture and forestry (13%), and transportation (6%). In addition to the multiple primary emissions, a variety of complex processes can generate secondary PM2.5 in the atmosphere from different precursors of yet different sources, as described in previous sections. Due to this complexity, it is much harder to estimate a “background level” of fine PM for a region compared to the above exercise for CO; the furthermore, much shorter lifetime of fine PM with precipitation being its most effective atmospheric removal mechanism, makes such an approach even more difficult. Making use of the FAQS resources, the OLC-PM2.5 mass measurements are being compared in Figure 38 with the other FAQS sites along Georgia’s fall-line, and with four of Georgia’s regulatory monitoring sites operated by the EPD in Columbus and Augusta. 
Figure 38: Monthly time-series of 24h average [PM2.5] from the 4 major FAQS sites and 4 FRM sites in Augusta (red) and Columbus (blue); incl. areas burnt on Forts Benning and Gordon. The EPD operated sites are part of U.S. EPA’s NAMS/SLAMS network, monitoring criteria pollutants, incl. 24-h integrated PM2.5 mass following the Federal Reference Method (FRM) as described in the Code of Federal Regulations [CFR, 1997]. Two FRM sites are in Columbus at Cusseta Road and the County Health Department, about 5 km and 11 km north of OLC, respectively, hence further away from Fort Benning. The two Augusta FRM sites are the Medical College and Bungalow Road, each 18 and 19 km southeast from the FAQS Riverside Park site (see map in Fig. 4 for orientation), close to the eastern border of Fort Gordon. Note that the FRM sites represent 24h integrated (midnight to midnight) [PM2.5] based on Teflon filter samples collected on a one in three (1/3) day sampling schedule. The 1/3 day FRM values generally agree well with the FAQS values that were averaged from continuous TEOM measurements. Discrepancies seen between the three Columbus sites and the three Augusta sites respectively seem random and not systematically linked to burn activities on each installation. However, in some cases, e.g. on 12/3, 12/17, 1/28, 3/25, 4/3, 4/14, and 4/24, local impact from prescribed burning is evident. Especially the burnings in March and April can be regarded to represent more regional burning activities, since the [PM2.5] increases associated with those periods occurred region-wide, as indicated by the additional traces from the Griffin and Macon sites. In contrast to the fall 2001 period, the 24h NAAQS of 65 μg m-3 was not exceeded on a single day during this burn season at any of the FAQS or FRM sites part of this analysis. What effect this had on the annual average [PM2.5] for the region is discussed next by means of Figure 39. 
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