## 3 Results and Discussion  
### Dust Emission  
The exposure of re-suspended soil dust emissions from harvesting operations varies across the production land area. The spatial distribution of dust emission primarily depends on the distribution of silt content in the soil which ranges from 28.76% to 31.70% for PM\({}_{2.5}\) and from 33.34% to 40.36% for PM\({}_{10}\) across the production areas (assuming the same harvesting system is applied to all production areas). The estimation of the emission factor was based on dry day conditions with precipitation less than 0.01 inch per day and extrapolated for the entire production areas. Figure 4 shows expected spatial distribution of emission factor for PM\({}_{2.5}\) (Figure 4a) and PM\({}_{10}\) (Figure 4b). The emission level released from vehicle movement within the feedstock production land varies according to location. The spatial distribution of PM\({}_{10}\) emission is not equally spread across the production land area. The color trend displayed in the figure moves from dark blue to yellow and then to red which represents an increasing emission factor across the areas. Higher emission results for areas where production is highly concentrated due to intensive harvesting operations. These higher production areas (in red) are located at higher elevation levels and farther away from the coast. The highest emission factor which appears as a dark red color has a value of 46.74 lbs/VMT while the lowest emission factor is 39.36 lbs/VMT and appears as a dark blue color (Figure 4b). Although there are differences in PM\({}_{2.5}\) emission across the production areas, the variation is small, ranging from 3.45 to 3.76 lbs/VMT. The average emission factor across the production areas is estimated at 3.62 lbs/VMT for PM\({}_{2.5}\) and 42.73 lbs/VMT for PM\({}_{10}\) (see Table 2)  
Re-suspended dust emissions originating from mechanical harvesting consist of three operations: (i) crop handling by the harvesting machine, (ii) transloading of the harvested crop into trucks/trailers and (iii) field transport [6; 34]. Given limited data on the technical aspects of machine harvesting, estimation of crop handling and truck transloading processes are not included in this study. The above dust emission analysis (Table 2) is calculated for dust emitted from in-field movement of harvesters and trucks/trailers only. A number of studies have conducted analyses on dust emission factors for agricultural mechanical harvesting. Section 9 of EPA's Compilation of Air Pollutant Emission Factors (AP-42) reported detailed dust emission for PM\({}_{7}\) from each operation for cotton, wheat and sorghum crops [6; 34]. The highest \begin{table}
\begin{tabular}{c c c} \hline \hline
**Content** & **Unit** & **EPM\({}_{2.5}\)** & **EPM\({}_{10}\)** \\ \hline Emission factor per vehicle mile traveled & lbs/VMT & & \\ Minimum & & 3.45 & 39.36 \\ Maximum & & 3.76 & 46.74 \\ Average & & 3.62 & 42.73 \\ Standard deviation & & 0.06 & 1.78 \\ Emission factor per acre & lbs/acre & & \\ Minimum & & 5.30 & 60.56 \\ Maximum & & 5.79 & 71.90 \\ Average & & 5.57 & 65.74 \\ Standard deviation & & 0.09 & 2.73 \\ Total emission factor per year & Tons/year & 21.84 & 248.18 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Emission factor for PM\({}_{2.5}\) and PM\({}_{10}\) produced by mechanical harvesting operations. Figure 4: (a) Expected spatial distribution of emission factor for PM\({}_{2.5}\) and (b) PM\({}_{10}\) within the feedstock production areas. PM\({}_{7}\) emission was found for harvesting cotton with an emission level of 0.0086 lb/acre [6; 34]. This number is much small than the average PM\({}_{2.5}\) emission of 5.57 lbs/acre as analyzed in this study. Usually one would expect the emission level to be higher for PM\({}_{7}\) as compared to PM\({}_{2.5}\). This comparison suggests that dust emission from banagrass harvesting is much higher than cotton, wheat and sorghum crops as reported in the EPA (2006b).