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Env Scin 297 > Intro to Aerosol > Flashcards

Intro to Aerosol Flashcards

1
Q

What are the sources of aerosol?

A

Vehicle emissions, bulk to particle conversion

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2
Q

What are the common examples of aerosol?

A

black carbon, dust particles, pollen, sea salt

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3
Q

how does cloud droplets form?

A

aerosol compounds attract water and become bigger as more vapor condenses

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4
Q

what are the two types of effects of aerosol?

A

direct and indirect

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5
Q

what kind of aerosol purely scatters light?

A

white particles like sea salt

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6
Q

what kind of aerosol cause heating?

A

black aerosols like black carbon absorbs heat

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7
Q

what is indirect effect?

A

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

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8
Q

what kind of scattering is for molecules and atoms?

A

rayleigh scattering

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9
Q

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

A

mie scattering

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10
Q

what kind of scattering for larger particles like water droplets?

A

geometric scattering

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11
Q

what is the size range for aerosols?

A

1 nm to 100 microns

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12
Q

what is the size range for ultrafine?

A

1 nm to 100 nm

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13
Q

what is the size range for fine particles?

A

100 nm to 1 microns

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14
Q

what is the size range for coarse particles?

A

1 micron to 100 microns

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15
Q

what are the four modes in the atmosphere?

A

course, accumulation, aitken, nucleation

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16
Q

what is the size range of coarse mode

A

1 micron to 100 microns

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17
Q

size range of accumulation mode?

A

100 nm to 1 micron

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18
Q

size range of aitken mode?

A

10 nm to 100 nm

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19
Q

nucleation mode?

A

1 nm to 10 nm

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20
Q

what are the examples of spherical aerosols?

A

droplets, fly ash, inorganic salts

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21
Q

what is the mean free path?

A

distance travelled by a molecule before colliding to another molecule

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22
Q

What is drag force?

A

forced exerted by the stagnant gas on a moving body

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23
Q

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

A

cunningham correction factor

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24
Q

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

A

It increases because the particles experience less drag force

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25
Q

what is mechanical mobility?

A

the ratio of particle velocity and drag force

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26
Q

what is sedimentation velocity?

A

it is when drag force is equal to the gravitational force

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27
Q

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

A

lower particle means lower settling velocity and lower relaxation time

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28
Q

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

A

the drag force increases

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29
Q

What are the different types of particle diameter?

A

stokes, aerodynamic, optical

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30
Q

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

A

stokes diameter

31
Q

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?

A

aerodynamic diameter

32
Q

what are latex particles

A

particles that have known stokes diameter and refractive index

33
Q

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

A

divide N (height) by log (delta D_p)

34
Q

What describes the log-normal distribution?

A

the geometric mean diameter and standard deviation

35
Q

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

A

total particle number concentration

36
Q

what do we use in bipolar diffusion charging?

A

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

37
Q

what are the forces involved in bipolar diffusion charging?

A

coulumb force, image force, diffusion

38
Q

which charge is greater in fraction in bipolar charge distribution?

A

negative charges hence shifted to the left

39
Q

which ions have higher mean electrical mobility?

A

negative ions

40
Q

what are the advantages of bipolar charging?

A

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

41
Q

what are the disadvantages of bipolar charging?

A

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

42
Q

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

A

gunn distribution

43
Q

what is Fuchs-distribution

A

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

44
Q

what is used in unipolar diffusion charging

A

corona needle

45
Q

what are the advantages of unipolar charging?

A

works well for ultrasize range

46
Q

what are the disadvantages of unipolar?

A

time dependent, broad distribution for fine range

47
Q

what is electrical mobility

A

ratio of particle velocity and drag force

48
Q

what dictates electrical mobility?

A

number of charge and particle diameter

49
Q

what diameter dictates the lower detection efficiency of a CPC?

A

kelvin diameter where evap = condensation

50
Q

higher temperature difference of saturator and condenser means?

A

smaller lower detection efficiency

51
Q

what happens inside a modern CPC?

A

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

52
Q

how many particles are inside a room?

A

5000 - 10000 particles

53
Q

what is the limit of efficiency of a cpc?

A

around 10 nm low efficiency is observed

54
Q

where do we use water cpc?

A

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

55
Q

Where is the CPC first calibrated against?

A

NIST, NPL, PTB

56
Q

what is the true value of electrometer measurement?

A

0.95 due to internal losses

57
Q

What is the initial test for CPC performance?

A

plateau efficiency at 40 nm and cut diameter around 10 nm

58
Q

what should be done if the CPC fails its test?

A

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

59
Q

what is the area of dma transfer function?

A

0.5

60
Q

What is the DMA transfer function dependent?

A

sample flow ratio and particle size

61
Q

what is the transfer probability of the mean electrical mobility?

A

unity

62
Q

Where does the size resolution for a DMA depends on?

A

the ratio of aerosol flow and sheath air

63
Q

What defines the particle size range of a DMA

A

its geometry

64
Q

What are the disadvantages of DMA?

A

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

65
Q

What does monodisperse aerosol generator consist of?

A

polydisperse aerosol generator, bipolar charger, DMA

66
Q

what consists monodisperse aerosol?

A

single charge of smallest particle or multiple charge but larger particles

67
Q

What does TDMA do

A

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

68
Q

which is bigger, stokes diameter or aerodynamic diameter?

A

aerodynamic diameter

69
Q

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

A

optical diameter

70
Q

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

A

the distribution becomes broader

71
Q

what is the relationship of electrical mobility and temperature

A

inversely proportional

72
Q

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

A

17-27 degC

73
Q

how are impactors designed?

A

nozzle - impaction - plate config

Env Scin 297 (4 decks)

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