Toni atmosphere L4 Flashcards
(26 cards)
Define relative humidity
Relative humidity is the partial pressure of water in the gas phase compared to to what it would be for a saturated gas phase of water above pure water liquid at the same temperature
What does the relative humidity tell us
It provides a measure of how much water vapour the atmosphere holds compared to how much it could hold
What happens to aerosol particles as relative humidity changes
Aerosols can:
Absorb water from the air → swell in size
Lose water → shrink, possibly become solid
For inorganic salts and solution droplets what happens as water vapour evaporates
As water favour evaporates from an aqueous droplet salt concentration increases
For inorganic salts and solution droplets what happens as water condenses on it
The solution becomes more dilute
Describe what happens in phase equilibrium between a liquid and a gas
The chemical potential of liquid water equals that of water vapour
µg(p,T) = µl(p,T)
What does the Clausius-clapeyron equation describe
The Clausius-clapeyron equation explains how Vapor pressure changes with temperature
What is the triple point
The triple point is where solid, liquid and gas coexist
What does relative humidity control
Controls whether aerosols gain or lose water
Describe vapour pressure of solutions where the solute is non volatile
If a solute is non-volatile, it doesn’t enter the gas phase and only the solvent contributes to the vapour pressure
Describe vapour pressure of solutions where the solute is volatile
Solutions with a volatile solute produce a vapour which is a mixture of both solvent
and solute
Describe an ideal solution
Ideal solution: solute-solvent interactions are like solvent-solvent ones.
Describe a real solution
Real solution: interactions are more complex → vapor pressure predictions require corrections.
What is Raoult’s law
Raoult’s Law states that the partial vapor pressure of a component in a solution is proportional to its mole fraction in the liquid.
For an ideal solution only
Pa = XaPa*
Describe the water activity at equilibrium
Water activity = Pa/Pa* = RH = S
What is the critical condition
This is the critical condition: the water activity inside the droplet must equal the RH of the air for the system to be stable.
What happens when RH>aw
Droplet grows and condenses water
What happens when RH<aw
Droplet shrinks, evaporates water
How do we calculate the mass growth factor
Gm(RH) = m wet(RH)/mdry
What is used as a calibration for and instrument measuring hygroscopic growth and why
Sulphuric acid is often chosen as a calibration for an instrument measuring hygroscopic growth as it absorbs and desorbs water continuously with no phase transitions
Define phase transition
A phase transition in aerosols is when a particle changes between solid, liquid, or semi-solid as the humidity (or temperature) changes.
What is the deliquescence point
a solid salt particle takes up water and becomes a liquid droplet
What is the efflorescence point
The efflorescence point is the relative humidity below which an aqueous aerosol droplet crystallizes and becomes a solid particle.
Why does supersaturation occur upon drying
The deliquescence point and the efflorescence points do not occur at same RH. On drying supersaturated solutions can form as there are no heterogeneous nuclei/ surfaces on which crystallisation can occur
