Aerosol Microphsyics 1

Question 1

What groups can secondary atmospheric particles be divided into?

Answer 1

1. New particle formation (NFP) from gaseous precursors
2. Condensation of gases on already existing surfaces

Question 2

What sizes must newly formed and particles grow to before they influence climate?

Answer 2

Over 50-100nm in diameter

Question 3

What does NFP stand for?

Answer 3

Newly formed particles

Question 4

What is aerosol Nucleation?

Answer 4

The Nucleation of trace substances and water from the vapour phase to the liquid or solid phase

Question 5

What is aerosol Nucleation the first step in?

Answer 5

The phase transition process

Question 6

What are the requirements/steps for the production of new particles by gas-to-particle conversion?

Answer 6

1. Critical embryo/thermodynamically stable cluster ~1nm must be formed
2. Once formed these clusters can grow rapidly through condensation and/or coagulation to quasi-stable sizes of 3-4nm Dp
3. Survival beyond this size is rare and depends on numerous competing processes

Question 7

What is supersaturation of vapour phase required for?

Answer 7

Nucleation

Question 8

What is supersaturation?

Answer 8

Relative humidity > 100%

Question 9

What does RH stand for?

Answer 9

Relative humidity

Question 10

What happens to molecules and clusters in supersaturated vapour?

Answer 10

There’s a higher conc of molecules and clusters

Question 11

How are molecular clusters formed?

Answer 11

By gas phase collisions and attachment of molecules to reach a critical size at which they can grow further by condensation

Question 12

What is homogeneous Nucleation?

Answer 12

The self-Nucleation of one or more species in the absence of a pre-existing surface

Question 13

What is heterogeneous Nucleation?

Answer 13

The Nucleation of one or more species onto a pre-existing surface

Question 14

What is the most common Nucleating agent?

Answer 14

Sulphuric acid

Question 15

What happens in NPF after stable clusters are formed?

Answer 15

Other substances such as low-volatility organics can take part in the growth process

Question 16

Once particles grow to a big enough size in NPF what can happen?

Answer 16

They can act as nuclei on which cloud droplets then form by condensation of water vapour

Question 17

What conditions are needed for Nucleation to occur?

Answer 17

Needs to be high enough concs of nucleating vapours produced from photo-oxidation of atmospheric gases
(E.g. sulphur dioxide and volatile organic compounds)

Question 18

What does the low volatility of sulfuric acid lead to?

Answer 18

It’s easily supersaturated and the gaseous sulphur dioxide can begin to condense

Question 19

When does NPF start?

Answer 19

Around midday

Question 20

Why does NPF start around midday?

Answer 20

Because it requires sunlight

Question 21

The fact that NPF starts around midday causes the NPF growth graph to look like what?

Answer 21

A banana

Question 22

Where are aerosol Nucleation events frequently observed?

Answer 22

In the free troposphere and under remote, urban, forested, and marine environments of the lower troposphere

Question 23

What two main processes control the transformations of particles?

Answer 23

Condensation and coagulation

Question 24

Do all Nucleation events create clouds?

Answer 24

No

Question 25

Give an example of a Nucleation event that doesn’t lead to a cloud

Answer 25

Local kelp and algae blooms that create aerosols but particles don’t get high enough or high enough conc to form cloud

Question 26

Describe the process of coagulation

Answer 26

1. Aerosol particles collide with one another due to relative motion between them
2. They become so close that Van-der-waals forces bind them together
3. They form a larger particle

Question 27

What is kinematic coagulation?

Answer 27

When relative motion arises from external forces I.e. gravity, electrical forces, aerodynamic effects

Question 28

What is thermal coagulation?

Answer 28

When the relative motion is due to brownian motion

Question 29

How does coagulation affect number of particles?

Answer 29

Decrease no. Small particles, doesn’t affect no. Big particles

Question 30

What does the rate of coagulation depend on?

Answer 30

-diameter of larger particles
-diffusion rate of smaller particles
-conc of large and small particles

Question 31

Define particle formation rate

Answer 31

The flux of growing nanoparticles through a certain diameter size barrier

Question 32

What are the 2 macroscopic scale properties relevant for analysis particle growth?

Answer 32

Particle formation rate (J)
Particle growth rate (GR)

Question 33

What does particle growth rate mean?

Answer 33

Reasonably well-separated mode of particles undergoing a growth into larger sizes

Question 34

Under most atmospheric conditions, what is the dominant removal mechanism for atmospheric Nucleation mode particles?

Answer 34

Coagulation with larger particles

Question 35

What is the removal of Nucleation mode particles strongly tied to?

Answer 35

Timescales for growth to larger sizes by condensation and self-coagulation

Question 36

What happens in slow nuclei growth?

Answer 36

Particles are quickly scavenged away and have practically no atmospheric relevance

Question 37

What happens in fast nuclei growth?

Answer 37

Significant fraction of particles can survive and eventually modify the entire particle population

Question 38

what is turbulent diffusion?

Answer 38

turbulent eddies bring material close to the surface

Question 39

what is brownian motion? (dry deposition)

Answer 39

random brownian motion causes them to collide with any nearby surfaces

Question 40

what is gravitational settling?

Answer 40

large particles are pulled to surface due to gravity

Question 41

what are two mechanisms that produce sea salt?

Answer 41

-direct production of sea-salt through spume
-indirect production of sea-salt aerosol through bubbles