Toni atmosphere L9 Flashcards
(26 cards)
What is molecular flux
Molecular flux means how many gas molecules hit the surface of the droplet each second
What is the accommodation coefficient
the accommodation coefficient tells us what fraction of gas molecules that hit the droplet actually stick or enter
Why is the accomodation coefficient important
if you are modelling how a gas enters a droplet you need to adjust for a, if you don’t you will overestimate how fast gas uptake happens
What does it mean when the accomodation coefficient =1
every molecules that hits the droplet enters
What does an acommodation coefficient of 0.1 mean
only 10% sticks, 90% bounces off
What does an accomodation coefficient of 0 mean
nothing enters and the surface is completely reflective
What is mass flux
Mass flux is a measure of how much mass moves through a surface per unit time and per unit area.
What does the regimes tell us
These regimes describe how gas molecules behave near a droplet
What is the regime based on
it is based on how big the droplet is compared to the average distance a gas molecule travels before colliding with another gas molecule
What are the 3 types of regime
free molecule regime
Transition regime
Continuum regime
what is the free molecule regime
Kn>1
gas molecules don’t collide with each other, the droplet is so small the gas molecules either hit the target or miss. The gas molecules behave like individual particles not a fluid
Where does the free molecule regime happen
for very small droplets
In low pressure environments
What is the continuum regime
Kn<1
The gas molecules collide many times before reaching the droplet, they behave like a continuous fluid. A vapour condensation gradient builds up around the droplet
Where does the continuum regimen happen
happens for large droplets
In normal atmospheric pressures
What is the transition regime
kn approximately 1
The droplet size is comparable to the mean free path. Some gas molecules act like in the free molecule regime and some act like in the continuum regime
Where does the transition regime happen
For mid sized particles
In the accumulation mode of atmospheric aerosols
What regime does the nucleation mode fall into
free molecule regime, as the particles are too small
What regime does the accumulation mode fall into
transition to free-molecule regime depending on altitude
What regime does the coarse mode fall into
coarse mode large particles, gas molecules collide with each other a lot before reaching them
What is the Fuchs-sutugin correction
Fuchs–Sutugin correction, is used to calculate the mass flux of gas onto aerosol particles when they fall in the transition regime
What is the uptake coefficient
What fraction of gas molecules that hit the surface of a particle or droplet actually enter and react or dissolve.
What factors affect the uptake coefficient
Diffusion
Surface accomodation
Solvation
How does diffusion affect the uptake coefficient
Diffusion affects the uptake coefficient by controlling how quickly gas molecules reach the droplet. If diffusion is slow, fewer molecules hit the surface, which lowers the uptake coefficent
How does surface accomodation affect the uptake coefficient
The proportion of colliding molecules which become incorporated into the particle
must be considered. If less than 100% of the molecular collisions lead to incorporation then the mass flux will be diminished
