3506B24 Final Report
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- 5 METHODOLOGY 5.1 Data Collection at OLC
- Figure 10
In the case of the first two NAAQS exceedances on 10/29 and 10/30, a distinct discrepancy exists between the GFC plume trajectory, predicting westerly flow, and the observed easterly direction. Also the wind speed had been predicted much greater than the actually observed daytime maxima. Furthermore, the forecast predicted relatively deep and uniform BL heights during this last week of October, but the local measurements in maximum and minimum air temperature indicate significant nighttime cooling, giving rise for stable nocturnal BL and near surface stratification, with the effect of inhibited dilution of surface emissions such as smoldering biomass. Although the GFC forecast may predict well the average conditions for the larger region, representing a clustered area comprised of several counties, its spatial resolution seems insufficient to predict local phenomena, as they appeared in the much smaller Fort Benning and Columbus area. In addition, it seems important to stress the nighttime forecasts over the daytime, in order to estimate the potential local impact of the PB emissions. The last two exceedances on 11/16 and 11/17, seemed driven largely by burns that started as uncontrolled wild fires near the large artillery impact areas (A13, K13, and K14) as a result of artillery training activities, but were labeled prescribed burns for inventory purposes. This period was also characterized by northeasterly flow under clear sky conditions, as indicated by the difference in nighttime vs. daytime temperature and wind speed, and presumably shallow nocturnal inversion layers. A more thorough evaluation of the relationship between burn activities, meteorological conditions and measured [PM2.5] follows. The following Figure 9 correlates average 24 h PM2.5 concentrations measured midnight-to-midnight at OLC with prescribed burn (PB) or wild fire (WF) acres burnt, considering the fire location (distance and direction) relative to OLC, and the projected plume trajectory (PPT), i.e. the cosine of the angle between the direction of the fire from OLC and the wind direction, assuming wind measurements at OLC are representative of the greater surrounding area. Hence, the potential plume impact at OLC is considered largest if PPT equals 1, putting the fire directly upwind. Other parameters included in this comparison here, are the difference between daily maximum and minimum temperature (lower atmosphere stability indicator), the 24 h average wind speed, the GFC model predicted boundary layer mixing height (BLH) for the day the burn or wild fire occurred as well as for the succeeding night. The Figure illustrates and enforces the relationships mentioned above, in that the fine PM concentration is most sensitive to wind speed and atmospheric stability, leading to PM accumulation under calm conditions especially associated with nocturnal inversions. However, the illustration reveals also uncertainties in wind direction measurements and plume trajectory calculations for such calm conditions, and the difficulty to predict boundary layer mixing heights that effectively promote dilution of fine PM emitted near the ground at day, or on the other hand trap PM that are being emitted at night. The Figure however more clearly indicates that under stagnant atmospheric conditions smoldering fires represent a significant source for additional local air pollution extending continued emissions into the lower atmosphere over the next day or more, until the weather pattern changes significantly. 
Figure 9: Correlation of 24 h average PM2.5 concentrations at OLC with total acres burnt, considering the fire location (distance and direction) relative to OLC, and the projected plume trajectory as a measure for potential plume impact at OLC (largest if equal 1, placing OLC directly downwind), with the lower atmosphere stability indicator (Tmax - Tmin), the 24 h average wind speed (top), and with the GFC model predicted boundary layer mixing height (BLH) for the day the burn or wild fire occurred as well as for the succeeding night (bottom). The date labels in the legend (right) point to a continued accumulation of fine PM pollution and contribution from smoldering fires until several days after the actual flaming stage. 5 METHODOLOGY 5.1 Data Collection at OLC 5.1.1 Site Preparation, PM2.5 Sampling, and Meteorology The Oxbow Meadows Environmental Learning Center (OLC) is an educational outreach program run by the Department of Biology of the Columbus State University, in association with the Columbus Water Works. Constructed wetlands and the southern terminus of the Columbus Riverwalk characterize the property. The monitoring shelter was established during the Phase I of the FAQS field study in July 2000 and stationed on a large grassy field between the parking lot and the Environmental Learning Center; see FAQS [2001] for more details. This site is approximately 5 miles south of downtown Columbus and less than one mile west of the western border of Fort Benning’s military installation (32.3871 N latitude, 84.959 W longitude, 74 m asl), see maps in Figs. 4 and 5 above. As part of this project, and in preparation of the specific sampling needs, the OLC site has been upgraded by a sampling platform, a fence and additional electrical wiring, as illustrated in Figure 10. The sampling needs were met by a specific sample collection strategy involving four Particle Composition Monitors (PCM) and two High-Volume Samplers (HVS) as outlined in Table 4.  Download 11.49 Mb. Share with your friends:
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