Intro to Aerosol

Question 1

What are the sources of aerosol?

Answer 1

Vehicle emissions, bulk to particle conversion

Question 2

What are the common examples of aerosol?

Answer 2

black carbon, dust particles, pollen, sea salt

Question 3

how does cloud droplets form?

Answer 3

aerosol compounds attract water and become bigger as more vapor condenses

Question 4

what are the two types of effects of aerosol?

Answer 4

direct and indirect

Question 5

what kind of aerosol purely scatters light?

Answer 5

white particles like sea salt

Question 6

what kind of aerosol cause heating?

Answer 6

black aerosols like black carbon absorbs heat

Question 7

what is indirect effect?

Answer 7

aerosols can alter cloud’s albedo such that more aerosols means more scattering of light hence cooling

Question 8

what kind of scattering is for molecules and atoms?

Answer 8

rayleigh scattering

Question 9

what kind of scattering for particles about the same size of visible light wavelength?

Answer 9

mie scattering

Question 10

what kind of scattering for larger particles like water droplets?

Answer 10

geometric scattering

Question 11

what is the size range for aerosols?

Answer 11

1 nm to 100 microns

Question 12

what is the size range for ultrafine?

Answer 12

1 nm to 100 nm

Question 13

what is the size range for fine particles?

Answer 13

100 nm to 1 microns

Question 14

what is the size range for coarse particles?

Answer 14

1 micron to 100 microns

Question 15

what are the four modes in the atmosphere?

Answer 15

course, accumulation, aitken, nucleation

Question 16

what is the size range of coarse mode

Answer 16

1 micron to 100 microns

Question 17

size range of accumulation mode?

Answer 17

100 nm to 1 micron

Question 18

size range of aitken mode?

Answer 18

10 nm to 100 nm

Question 19

nucleation mode?

Answer 19

1 nm to 10 nm

Question 20

what are the examples of spherical aerosols?

Answer 20

droplets, fly ash, inorganic salts

Question 21

what is the mean free path?

Answer 21

distance travelled by a molecule before colliding to another molecule

Question 22

What is drag force?

Answer 22

forced exerted by the stagnant gas on a moving body

Question 23

what is the correction factor to compute for drag force for small particles i.e., <100 microns

Answer 23

cunningham correction factor

Question 24

what happens to mechanical mobility if we add the cunningham correction factor?

Answer 24

It increases because the particles experience less drag force

Question 25

what is mechanical mobility?

Answer 25

the ratio of particle velocity and drag force

Question 26

what is sedimentation velocity?

Answer 26

it is when drag force is equal to the gravitational force

Question 27

what is the trend between particle size and setting velocity and relaxation time

Answer 27

lower particle means lower settling velocity and lower relaxation time

Question 28

what happens to drag force when the dynamic shape factor is applied?

Answer 28

the drag force increases

Question 29

What are the different types of particle diameter?

Answer 29

stokes, aerodynamic, optical

Question 30

what is the diameter of a sphere that has the same density and settling velocity as the particle?

Answer 30

stokes diameter

Question 31

what diameter of a sphere whose density is same as water which settles in still air at the same velocity as the particle in question?

Answer 31

aerodynamic diameter

Question 32

what are latex particles

Answer 32

particles that have known stokes diameter and refractive index

Question 33

what can we do to be able to compare different concentrations in size bins with different size widths?

Answer 33

divide N (height) by log (delta D_p)

Question 34

What describes the log-normal distribution?

Answer 34

the geometric mean diameter and standard deviation

Question 35

what is zeroth moment? area under the curve of dN/dlog (Dp)

Answer 35

total particle number concentration

Question 36

what do we use in bipolar diffusion charging?

Answer 36

we ionize gases surrounding particles by alpha or beta radiation or x-ray

Question 37

what are the forces involved in bipolar diffusion charging?

Answer 37

coulumb force, image force, diffusion

Question 38

which charge is greater in fraction in bipolar charge distribution?

Answer 38

negative charges hence shifted to the left

Question 39

which ions have higher mean electrical mobility?

Answer 39

negative ions

Question 40

what are the advantages of bipolar charging?

Answer 40

time independent, narrow for small particles than 300 nm, simple to calculate

Question 41

what are the disadvantages of bipolar charging?

Answer 41

broad for big particles, greater than 300 nm, small particles are hard to charge

Question 42

what bipolar model only considers diffusion and is for greater than .1 microns?

Answer 42

gunn distribution

Question 43

what is Fuchs-distribution

Answer 43

takes into account diffusion and electrostatic, valid for entire submicron range

Question 44

what is used in unipolar diffusion charging

Answer 44

corona needle

Question 45

what are the advantages of unipolar charging?

Answer 45

works well for ultrasize range

Question 46

what are the disadvantages of unipolar?

Answer 46

time dependent, broad distribution for fine range

Question 47

what is electrical mobility

Answer 47

ratio of particle velocity and drag force

Question 48

what dictates electrical mobility?

Answer 48

number of charge and particle diameter

Question 49

what diameter dictates the lower detection efficiency of a CPC?

Answer 49

kelvin diameter where evap = condensation

Question 50

higher temperature difference of saturator and condenser means?

Answer 50

smaller lower detection efficiency

Question 51

what happens inside a modern CPC?

Answer 51

we let the aerosol to attract the condensable species such that it becomes bigger and easier to count

Question 52

how many particles are inside a room?

Answer 52

5000 - 10000 particles

Question 53

what is the limit of efficiency of a cpc?

Answer 53

around 10 nm low efficiency is observed

Question 54

where do we use water cpc?

Answer 54

It is applied for hygroscopic materials such that how does aerosol grow in increasing RH

Question 55

Where is the CPC first calibrated against?

Answer 55

NIST, NPL, PTB

Question 56

what is the true value of electrometer measurement?

Answer 56

0.95 due to internal losses

Question 57

What is the initial test for CPC performance?

Answer 57

plateau efficiency at 40 nm and cut diameter around 10 nm

Question 58

what should be done if the CPC fails its test?

Answer 58

adjust condenser temp to set the cut diameter to 10 nm then cleaning of CPC

Question 59

what is the area of dma transfer function?

Answer 59

0.5

Question 60

What is the DMA transfer function dependent?

Answer 60

sample flow ratio and particle size

Question 61

what is the transfer probability of the mean electrical mobility?

Answer 61

unity

Question 62

Where does the size resolution for a DMA depends on?

Answer 62

the ratio of aerosol flow and sheath air

Question 63

What defines the particle size range of a DMA

Answer 63

its geometry

Question 64

What are the disadvantages of DMA?

Answer 64

at ultrafine particle range, the transfer function becomes broader and maximum transfer decreases

Question 65

What does monodisperse aerosol generator consist of?

Answer 65

polydisperse aerosol generator, bipolar charger, DMA

Question 66

what consists monodisperse aerosol?

Answer 66

single charge of smallest particle or multiple charge but larger particles

Question 67

What does TDMA do

Answer 67

measure the mixing state of a defined particle size and is applied for hygroscopic models, volatility

Question 68

which is bigger, stokes diameter or aerodynamic diameter?

Answer 68

aerodynamic diameter

Question 69

if a spherical particle of unknown size has the same particle scattering, which diameter is equal?

Answer 69

optical diameter

Question 70

what happens to the bipolar charge distribution when you increase the diameter size?

Answer 70

the distribution becomes broader

Question 71

what is the relationship of electrical mobility and temperature

Answer 71

inversely proportional

Question 72

by how much is the temperature of the butanol-aerosol mixture decreased in the condenser?

Answer 72

17-27 degC

Question 73

how are impactors designed?

Answer 73

nozzle - impaction - plate config