Odor Modeling with Updated Meteorological Data: A Comparison of H2S Impacts using Standard Hourly ASOS and 1-minute ASOS Data

Due to the temporal and subjective nature of odors, odor modeling techniques have tended to be project specific. When used in the regulatory arena, odor modeling for compliance with odor standards and criteria have traditionally used models developed for and approved by federal, state, and local regulatory agencies. One critical model input that may play an important role in characterizing the short-term impacts often used for odor is the hourly meteorological data. Traditionally, this hourly data has been a single reading of wind speed, wind direction, etc. taken just before or after the hour, which was then used as a representative value for that hour of wind parameters. Recently, the national Climatic Data Center has begun archiving much shorter-term (2-minute) average wind speeds and reporting this data every minute of the hours. There has been concern that use of this new “1-minute” ASOS (Automated Surface Observations System) data in modeling might result in different modeling results and conclusions than found previously using the traditional hourly meteorological data especially in areas where there is the likelihood of a large number of calm conditions, and where the wind conditions are variable. The objective of the study presented in this paper is to explore this issue, especially as it pertains to odor assessment at wastewater treatment facilities.Three different municipal wastewater treatment plants – one in a densely populated urban area, one in a suburban setting, and the third in a relatively sparsely populated area in the southwest were evaluated. The three facilities include a variety of source types, including point, area, and volume sources, representative of the different processes at such facilities. All three plants were modeled for H2S using standard hourly average meteorological data. In this study, the three facilities were remodeled using the 1-minute ASOS data, and the results compared to those found using the standard hourly meteorological data. The results of the study are presented both in tabular format and in the form of isopleths showing lines of constant concentration, and the implications of the new meteorological data on the potential conclusions in going from one form of meteorological data to the other is discussed.