Air quality, AIr pollution, measuring techniques

1. Atmospheric
Stability
• Concepts are applied to
motions of air parcels in the
atmosphere
• The topic of stability in
atmospheric science is
important because the
formation of clouds is closely
related to stability or
instability in the atmosphere.

2. Adiabatic Lapse Rate
• Adiabatic processes do not exchange heat and they are reversible.
• For an air parcel, this means that no thermal energy is entering or
leaving the air parcel from the outside. However, internal processes
are allowed
• However, temperature changes in the air parcel can still occur, but it is
not due to mixing, it is due to changes in the internal energy of the air
parcel.
• To summarize, rising air parcels expand and cool adiabatically without
exchanging heat with the environment.

3. Dry Adiabatic Lapse Rate
• If an air parcel is dry, meaning
unsaturated, stability is relatively
straightforward.
• An atmosphere where the
environmental lapse rate is the same
as the dry adiabatic lapse rate,
meaning that the temperature in the
environment also drops by 9.8 K·km-1,
will be considered neutrally stable.
• After some initial vertical
displacement, the temperature of the
air parcel will always be the same as
the environment so no further change
in position is expected.
Air rises, expands, and cools at the dry adiabatic laps
rate, approximated as a 10°C decrease per km

6. Moist Adiabatic Lapse Rate
• When water vapor condenses, it goes from a higher energy
state to a lower energy state. Energy is never created nor
destroyed, especially in phase changes, the energy gets
released in the form of latent heat.
• As latent heat is added from the process of condensation, it
offsets some of the adiabatic cooling from expansion.
• Because of this, the air parcel will no longer cool at the dry
adiabatic lapse rate, but will cool as a slower rate, known as
the moist adiabatic lapse rate.

12. The atmosphere is said to be absolutely stable if the environmental lapse rate is less than the moist adiabatic
lapse rate. This means that a rising air parcel will always cool at a faster rate than the environment, even after it
reaches saturation. If an air parcel is cooler at all levels, then it will not be able to rise, even after it becomes
saturated

14. • The atmosphere is said to be absolutely unstable if the environmental lapse rate is greater than the dry adiabatic
lapse rate. This means that a rising air parcel will always cool at a slower rate than the environment, even when it
is unsaturated. This means that it will be warmer (and less dense) than the environment, and allowed to rise.
• The atmosphere is said to be conditionally unstable if the environmental lapse rate is between the moist and dry
adiabatic lapse rates. This means that the buoyancy (the ability of an air parcel to rise) of an air parcel depends
on whether or not it is saturated.