Gaussian dispersion of low-weight volatile fatty acids from a ground-level area
source was assessed using STINK (a research-grade, Gaussian plume model from Australia)
and AERMOD (an AMS/EPA regulatory model). The goal of this research was to determine if
these models could effectively utilize a back-calculation methodology to reasonably assess
the emission rate and near-source-dispersion of odorous compounds. VFAs were sampled at
six receptors using thermal desorption tubes in one experiment and solid phase
microextraction (SPME) fibers in a second experiment. Measured concentrations, when
compared with those predicted by STINK and AERMOD, showed good agreement. However,
better prediction by AERMOD, compared to STINK, was observed for the experiments
involving SPME sampling. The use of AERMOD, combined with the back-calculation approach
for the dispersion modeling of odorous constituents, appears promising.
The performance of AERMOD was also assessed using meteorological conditions averaged
over various time intervals. It was assumed that the average conditions observed during 1, 5,
15 and 30 minute intervals prevailed for the entire 1-hr modeling period. This showed that
selection of an appropriate averaging time for meteorological data is important for dispersion
modeling when forced to make assumptions about constant meteorological conditions as in
the case of Gaussian models like AERMOD.