Introduction
In earlier lessons we examined single electrolyte solutions and
their water content and phase state (solid or liquid) as a function of
relative humidity.
We used the simple version of
E-AIM Model III, which only considers species in the
particle phase. In this lesson, we will examine partitioning between the
condensed and vapour phases.
Preparation
Before starting, ensure that this browser window occupies only the
left half of your screen. You should leave enough
space for another browser window where you can
enter data into
E-AIM and read the results. If your screen is too small for
two windows, print out this tutorial and use this window to enter data and
read
E-AIM's results. In these lessons we assume that you will
have two browser windows open.
Select this
link to open a second browser window containing the data input page
for "comprehensive" calculations using Model III
(http://www.aim.env.uea.ac.uk/aim/model3/model3b.php). Arrange
the windows on your screen so that both are visible and the left window
contains this text.
The Lesson
This consists of the four sets of calculations described in the links below,
which should be done in the order listed.
You have completed Lesson 3, and learned that:
-
In a system containing a volatile salt the existence of a condensed phase,
either solid or liquid, depends on the vapour pressure product of the salt
(here pHNO3 × pNH3),
the quantity of the compound present, and the relative humidity.
-
The solid salt, which is most likely to be present at low relative humidity,
has an equilibrium vapour pressure product that varies with temperature. Only if the
product of the actual partial pressures of the gases exceeds this value
will the solid form.
-
At relative humidities above its deliquescence point a solid aerosol will
take up water and exist as an aqueous droplet. The vapour pressure product
in equilibrium with the droplet is always lower than that over the solid,
and decreases with increased relative humidity as the droplet
becomes more dilute. As the total amount of ionic material in the
system decreases the transition relative humidity at which the
HNO3(g) and NH3(g) gases condense to
form an aqueous droplet goes up.
Now proceed to Lesson 4, which examines the
properties of aerosol solutions containing more than one electrolyte.