Short-range Dispersion Models Research Articles

Evaluation of a Revised AERMOD Treatment of Plume Dispersion in the Daytime Elevated Stable Layer

Advanced dispersion models such as AERMOD specifically address the portion of a plume emitted in convective conditions that is sufficiently buoyant to rise into the stable layer above the elevated inversion. This portion of the plume mass is often referred to as the “penetrated plume” because that plume component breaks through the elevated inversion and penetrates into the stable layer aloft. A pre-mature mixing of the penetrated plume to the ground has been identified in the current formulation of AERMOD, which is the USEPA-preferred short-range dispersion model and used in several other countries. This behavior has been observed based on data from field studies where the model is found to overpredict ground-level concentration events due to the penetrated plume component, with the timing of these peak predictions too early in the day. A proposed update to AERMOD to address the penetrated plume issue (referred to as “HBP” for modifications particularly important for “highly buoyant plume”) is documented and evaluated in this manuscript. The revised approach involves a check on the convective mixing height for the current hour as well as the next hour to determine how much of the penetrated plume has been captured by the convective boundary layer by the end of the current hour. The amount of the penetrated plume mass that is allowed to mix to the ground in the HBP modifications depends upon the result of this calculation. The HBP modification has been evaluated as an update to AERMOD for 3 databases along with a sensitivity analysis of the effects of the HBP changes on a variety of stack heights and buoyancy fluxes. The findings of the evaluation indicate that the HBP changes to AERMOD result in reduced overprediction tendencies. “Implications Statement” for the HBP paper being submitted to JAWMA A proposed enhancement to AERMOD to address a pre-mature mixing of penetrated plume material to the ground has been performed by implemented and evaluated by the authors. The enhancement, referred to as the highly buoyant plume (HBP) is based on work developed by Dr. Jeffrey Weil. HBP is designed to better characterize the penetrated plume behavior in the model such that it aligns more closely with observations based on data from field studies.

VISUALISING URBAN AIR QUALITY USING AERMOD, CALPUFF AND CFD MODELS: A CRITICAL REVIEW

Abstract. Degradation of air quality level can affect human’s health especially respiratory and circulatory system. This is because the harmful particles will penetrate into human’s body through exposure to surrounding. The existence of air pollution event is one of the causes for air quality to be low in affected urban area. To monitor this event, a proper management of urban air quality is required to solve and reduce the impact on human and environment. One of the ways to manage urban air quality is by modelling ambient air pollutants. So, this paper reviews three modelling tools which are AERMOD, CALPUFF and CFD in order to visualise the air pollutants in urban area. These three tools have its own capability in modelling the air quality. AERMOD is better to be used in short range dispersion model while CALPUFF is for wide range of dispersion model. Somehow, it is different for CFD model as this model can be used in wide range of application such as air ventilation in clothing and not specifically for air quality modelling only. Because of this, AERMOD and CALPUFF model can be classified in air quality modelling tools group whereas CFD modelling tool is classified into different group namely a non-specific modelling tool group which can be implemented in many fields of study. Earlier air quality researches produced results in two-dimensional (2D) visualization. But there are several of disadvantages for this technique. It cannot provide height information and exact location of pollutants in three-dimensional (3D) as perceived in real world. Moreover, it cannot show a good representation of wind movement throughout the study area. To overcome this problem, the 3D visualization needs to be implemented in the urban air quality study. Thus, this paper intended to give a better understanding on modeling tools with the visualization technique used for the result of performed research.

Evaluating the use of outputs from comprehensive meteorological models in air quality modeling applications

Currently used dispersion models, such as the AMS/EPA Regulatory Model (AERMOD), process routinely available meteorological observations to construct model inputs. Thus, model estimates of concentrations depend on the availability and quality of meteorological observations, as well as the specification of surface characteristics at the observing site. We can be less reliant on these meteorological observations by using outputs from prognostic models, which are routinely run by the National Oceanic and Atmospheric Administration (NOAA). The forecast fields are available daily over a grid system that covers all of the United States. These model outputs can be readily accessed and used for dispersion applications to construct model inputs with little processing. This study examines the usefulness of these outputs through the relative performance of a dispersion model that has input requirements similar to those of AERMOD. The dispersion model was used to simulate observed tracer concentrations from a Tracer Field Study conducted in Wilmington, California in 2004 using four different sources of inputs: (1) onsite measurements; (2) National Weather Service measurements from a nearby airport; (3) readily available forecast model outputs from the Eta Model; and (4) readily available and more spatially resolved forecast model outputs from the MM5 prognostic model. The comparison of the results from these simulations indicate that comprehensive models, such as MM5 and Eta, have the potential of providing adequate meteorological inputs for currently used short-range dispersion models such as AERMOD.

Intercomparison of methods for parameterising components of the surface energy balance - a summary of Working Group 1 - COST 710 results

Working Group 1 of COST Action 710 investigated the use of meteorological pre-processors for short-range dispersion models for regulatory purposes. Two commonly used schemes for estimating boundary-layer fluxes from standard meteorological observations were intercompared using high latitude measurements from Sweden for spring/summer and winter conditions. Ground heat fluxes estimated with five different schemes were compared for data measured in Switzerland. The main results of these studies are presented.

Extension of an operational short-range dispersion model for applications in an urban environment

When operationally modelling dispersion of air pollutants over a city, "conventional" dispersion models are often used with modifications in some of the parameters, such as the roughness length. However, the presence of a roughness sublayer (RS) is usually neglected, although its turbulence structure is different from that in the surface layer. Therefore, in the present work a roughness sublayer for urban applications is introduced. The principle of the modification has already been tested by simulating two tracer experiments using a Lagrangian particle model, and it was shown that the introduction of an RS clearly improves the model performance for both experiments. In this paper, it is shown that the same holds for the introduction of the RS in the multi-source/multi-receptor Gaussian OML model. Its performance is investigated for the city of Zurich in the year 1990, when a detailed emission inventory and observations at 29 stations are available. It is concluded that the introduction of the RS increases the physical significance of the model in urban environments and thus the credibility of its predictions.

Possible influence of SO 2 deposition on to a forest on the ground level concentration calculated by short range dispersion models

Wind-tunnels enable the behaviour of a plume in the atmospheric turbulent boundary layer to be studied in regions where the concentration of a pollutant is not modified much by deposition on to the ground. It is possible to make simple corrections to the predicted concentration taking deposition into account. It appears that in some cases, particularly in wet conditions, the influence on the concentration near the ground may be appreciable.