Model coupling and atmospheric dispersion of malodorous compounds over coastal regions

We conduct an atmospheric dispersion study of malodorous compounds emitted from a pulp mill plant over coastal regions of the Uruguay River in South America. A total of 11 events are simulated in which the authorities received complaints from the local population about the presence of malodorous substances in the area, with indication of date, hour and location of the event. The simulations are performed with an atmospheric dispersion model coupled to a boundary layer forecast model, and the modeled plumes and wind forecasts are validated with local information. The transport and diffusion of malodorous compounds is simulated with the Advanced Regional Prediction System (ARPS, University of Oklahoma), coupled to the operative Boundary Layer Forecast Model (BLM, National Meteorological Service of Argentina). ARPS performs the transport and diffusion calculations and BLM provides the 1-km horizontal resolution 3D meteorological fields required by ARPS as initial and boundary conditions. BLM has been specifically developed for modeling low-level atmospheric circulations over coastal regions where the daily cycle of water-land thermal contrasts at the surface is the major driving mechanism for the atmosphere. The validation of BLM winds with the observations from a 42 m meteorological tower indicates reasonably accurate wind forecasts. The spatial layout of modeled plumes is compared with the geographical distribution of points in the area where authorities received the complaints of the local population about the presence of malodor. Nine of the 11 studied events are considered successful modeling cases since a positive (negative) in situ verification of malodor presence matches with a plume position over (far from) the site. In one of the two unsuccessful modeling cases, although the plume is marginally distant from the site, the average wind direction error is the largest one of all the events. In the other case the modeled plume is in fact over the site, but the situation was negatively verified. The reason for the disagreement could be the wind direction changes during the event. This was the longest modeled case that lasted for 7 hours and the plume was meandering during that time; first from SSW to the S, then back the SSW, and finally to the S and SSE. The conclusion of the study is that, despite the inherent uncertainty of numerical simulations, the implemented modeling system proves to be a useful tool not only for diagnostic studies but also for preventing conflictive situations since it can produce reasonably accurate forecast of plume position and its potential impact.