Kathmandu University
Dhulikhel, Kavre
Environmental Modelling
ENVS 404
Lab Report – 9: Fugacity based multimedia modeling
2nd August, 2021
Submitted by:
Lakisha Shrestha
Roll no. 27
ENE 4th year
Submitted to:
Dr. Kundan Lal Shrestha
Department of Environmental
Science and Engineering
Fugacity based multimedia modeling
Objective
Fugacity based multimedia models are utilized to study and predict the behavior of chemicals in
different environmental compartments. Most chemicals have the potential to migrate from the
medium to medium. This is a continuous process and is affected by the properties of media that
the chemical is present in.
Introduction
a. Background
The models are formulated using the concept of fugacity, which was introduced by Gilbert N.
Lewis in 1901 as a criterion of equilibrium and convenient method of calculating multimedia
equilibrium partitioning. There are four levels of multimedia fugacity Models applied for
prediction of fate and transport of organic chemicals in the multi-compartmental environment.
Here, we use the level II which is an open system in equilibrium where Equilibrium between
compartments according to thermodynamics is assumed and continuous emissions and
transformation are also taken into account.
b. Principle
This model is based on the concept of fugacity, f, which is a measure of is a measure of the
“escaping” or “fleeing” tendency of a chemical from its immediate surroundings. It is identical to
partial pressure in ideal gases and is linearly or nearly linearly related to concentration.
Mathematically, fugacity of chemicals describes the rates at which chemicals diffuse, or are
transported between phases. The transfer rate is proportional to the fugacity difference that exists
between the source and destination phases. It is related to concentration of chemical, C, in the
phase by the equation:
𝑓 = 𝐶
𝑍
where, Z is the fugacity capacity of the phase.
The value of Z depends on the chemical and can be calculated using the equilibrium partitioning
coefficients of the chemicals, Henry’s law constant and other related physical-chemical properties.
The value of f is same for a system that is at equilibrium for each media. Fugacity capacity depends
upon the nature of chemical, nature of media, and temperature
c. Modelling applications
The model can help in identification of the relative importance of chemical specific
partitioning and transformation.
It can help in determination of bioaccumulation in organisms in different trophic levels of
the food web and in checking the consistency of monitoring data
It can be used for the prediction of chemical distribution, the result of which can be useful
in understanding the fate and transport of the chemical in a multimedia environment.
It can act as a decision supporting tool documenting the sources and nature of contamination
and feasible remedial strategies.
It can be used to understand a chemical’s behavior in the natural environment, which can
then be put to use in designing a chemical with desired environmental characteristics,
managing environmental emissions of said chemical, ranking chemicals, and environmental
policy making.
Modelling methods
For building the model, the initial step is to set up a mass balance equation for each phase in
question that includes fugacities, concentrations, fluxes and amounts. The values for different
characteristics of the media like it’s volumes (Vi), fugacity capacities (Zi), advective flows through
compartments (Gi), inflow concentrations (CB,i), and the first order reaction rates (ki) are also
required. The Z values for air (1), water (2), soil (3), and sediment (4) compartments can be
calculated from the physical-chemical properties of the chemical as follows:
𝑍1= 1
𝑅𝑇 𝑍2= 1
𝐻
𝑍3= 𝐾𝑠−𝑤𝑍2= 0.41𝑌
𝑠𝑜𝑖𝑙𝐾𝑂−𝑊𝜌𝑠𝑜𝑖𝑙
𝑍4= 𝐾𝑠−𝑤𝑍2= 0.41𝑌
𝑠𝑒𝑑𝐾𝑂−𝑊𝜌𝑠𝑒𝑑
Here,
R = Ideal gas constant
T = Absolute temperature
H = Henry’s constant of the chemical
Y = Organic content of soil or sediment
KO-W = Octal-water partition coefficient of the chemical
𝜌 = density of soil or sediment
