Estimation of point-source emissions of hydrogen sulfide and ammonia using a modified Pasquill-Gifford approach

Estimation of point-source emissions based on measured downwind concentrations and known meteorology is a challenging task. A facility to study atmospheric dispersion of hazardous gases has been designed and implemented at the Wind Engineering Research Field Laboratory (WERFL) at Texas Tech University in Lubbock, Texas. The field lab features a 48.5 m (160 ft) meteorological tower which can monitor wind speed at six heights, wind direction and vertical temperature gradients using temperature measurements at two elevations. The relative humidity and barometric pressure can also be monitored. A description of the facility and its features are provided in this paper. In this work, the Pasquill-Gifford (PG) model was modified to provide predictions of emission rates for two hazardous gases; hydrogen sulfide (H2S) and ammonia (NH3). Two mathematical manipulations of the PG model were used to refine estimates of emission rates of H2S and NH3 based on experimental field data. The first modified PG approach was based on an empirical correction to the Gaussian model, and was evaluated only for direct downwind distances and neutral atmospheric stability conditions. The second approach was based on an improved procedure for estimation of the specific dispersion coefficients for H2S and NH3 required in the PG model. These new dispersion coefficients were estimated from experimental data obtained in the field under both neutral and stable atmospheric conditions.