First Principles - Sustainable Design: The Science of Sustainability and Green Engineering - page 38

Figure 2.3 Two types of control
volumes when considering
environmental mass: (a) control
volume of an environmental
matrix (e.g., soil, sediment, other
unconsolidated material) or fluid
(e.g., water, air, blood); (b) a
pond. Both volumes have equal
masses entering and exiting, with
transformations and physical
changes taking place within the
control volume.
From D. A. Vallero, Environmental
Contaminants: Assessment and
Control , Elsevier Academic Press,
Burlington, MA, 2004.

Mass input

Mass output

Chemical and
biological
reactions and
physical change

Fluid transport
into control
volume

Fluid transport
out of control
volume

(a)

Input to atmosphere
from aerosols

Atmospheric deposition

Discharg Discharge from outfall

Stream input

Gas exchange

Output to stream

Sorption

Dissolution

Output to groundwater

Output to sediments

Groundwater input

Control volume boundary Control volume boundary

Sediment input

(b)

from others. A property must be able to be stated at a specific time independent
of its value at any other time and unconstrained by the process that induced the
condition (state). An intensive property is independent of the system's mass (such
as pressure and temperature). An extensive property is a proportionality to the mass
of the system (such as density or volume). Dividing the value of an extensive
property by the system's mass gives a specific property ,suchas specific heat, specific
volume, or specific gravity.