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Aerosols, Clouds, Atmospheres > Aerosols > Flashcards

Aerosols Flashcards

1
Q

Why is studying aerosols important for air quality and health?

A

-Exposure to particulate matter decreases life expectancy of every person by almost 1 year
-Life expectancy could be increased by ~2 years in most polluted cities if long term PM2.5 was decreased to EU WHO guideline level

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2
Q

Why is studying aerosols important for visibility?

A

High aerosol concentrations can lead to visibility issues e.g. planes not being able to fly

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3
Q

Why is studying aerosols important for climate?

A

Aerosols can have both a positive and negative radiative effect, but usually negative

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4
Q

Why is studying aerosols important for fertilisation?

A

Aerosols fertilise land and oceans (leading to eutrophication)

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5
Q

What questions should we be asking about climate change?

A

-how is the radiative balance of the Earth changing?
-how much of this is human caused?
-what are the impacts of this change?

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6
Q

Where do the measurements for probability density function come from? (PDF vs radiative forcing graph)

A

From climate models

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7
Q

How can the impact of aerosols be seen in history?

A

Red skies in paintings

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8
Q

What is an aerosol?

A

A dispersion of solid and liquid particles suspended in gas

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9
Q

What is the main characteristic of aerosols?

A

They are disperse

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10
Q

What are monodisperse aerosols?

A

All the suspended particles have the same size

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11
Q

Where do monodisperse aerosols come from?

A

Usually the lab

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12
Q

What are polydisperse particles?

A

A wide range of particle sizes

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13
Q

Where do polydisperse aerosols come from?

A

Usually natural, generated by several different mechanisms

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14
Q

How is aerosol particle size defined?

A

Either by diameter Dp or radius Rp

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15
Q

What measurements are aerosol diameters given in?

A

Microns or nm

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16
Q

What is a micron in nm

A

1 micron = 1000nm

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17
Q

What is 1nm in microns?

A

1 nm = 0.001 micron

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18
Q

What is the range of sizes for aerosol diameter?

A

A few nm to tens of microns

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19
Q

Why is there a very large range of particle masses

A

Mass of 1 micron particle equal to mass of 100nm particles

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20
Q

Why do assume particles to be spherical?

A

To more easily measure particle diameter

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21
Q

What are some natural aerosol sources?

A

Snow, salt spray, pollen, sand, dust

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22
Q

What are some anthropogenic aerosol sources?

A

Smoke from burning fire, burning of fossil fuels, burning fuel/petrol

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23
Q

What are externally mixed aerosol particles?

A

Where each particle is physically separated from the other components

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24
Q

What are internally mixed aerosol particles?

A

A homogeneous material reflecting the chemical and physical average of the contributing components

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25
Q

What are primary aerosols?

A

Aerosols emitted directly into the atmosphere

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26
Q

What are some natural sources of primary aerosols?

A

Volcanoes, forest fires, sea spray, wind borne dust

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27
Q

What is an anthropogenic source of primary aerosols

A

Fossil fuel burning

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28
Q

What is a secondary aerosol?

A

Aerosols produced from precursor gases

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29
Q

How are secondary aerosols formed?

A

Formed in the atmosphere through gas-to-particle conversion of both natural and anthropogenic gaseous precursors such as dimethyl sulphide

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30
Q

What are the four aerosol modes?

A

Nucleation, Aitkin, accumulation, coarse

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31
Q

Do aerosols have a short or long lifespan?

A

Short lifespan

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32
Q

What is the distribution of aerosols like?

A

Highly variable both temporally and spatially

33
Q

What is the lifetime of aerosols in different parts of the atmosphere?

A

Few days to few weeks in boundary layer, up to 1 year in stratosphere

34
Q

Why does dust have a longer lifespan than sea salt?

A

Because sea salt has a higher affinity for water so is more likely to become part of a cloud

35
Q

What does AOT stand for?

A

Aerosol optical thickness

36
Q

What does AOD stand for?

A

Aerosol optical depth

37
Q

What are the peaks on aerosol size distribution graphs called?

A

Modes of aerosol size distribution

38
Q

What is AOD related to?

A

Related to the amount of light that has been scattered or absorbed in a column through the atmosphere and depends on wavelength

39
Q

What is the distribution of fine AOT like globally?

A

N. America and Europe: pollution
S. America and Southern Africa: vegetation fires
South and East Asia: pollution

40
Q

What is the distribution of coarse AOT globally

A

Africa: coarse dust
Southern Hemisphere: salt particles
Middle east/ East Africa/ South Asia: desert dust

41
Q

Why is it difficult to determine surface aerosol conc from current satellite instruments (4 points)

A

-they are sensitive to total column rather than surface conditions
-most satellite instruments cant distinguish particles close to the ground from those high in the atmosphere
-clouds tend to obscure the view of aerosols below
-bright land surfaces e.g. snow, desert sand cane impair satellite retrievals

42
Q

What suggested % of people breathe polluted air that exceeds WHO reccomended level of 10mg/cm3

A

Over 80%

43
Q

What does N represent in aerosol data?

A

Aerosol particle concentration
-defined as no. Particles per unit volume

44
Q

What does PM10 mean?

A

Mass of particles with Dp > 10 microns

45
Q

What is the diameter of nucleation mode aerosols?

A

1-10nm

46
Q

What is the diameter of Aitken mode aerosols?

A

10-100nm

47
Q

What is the diameter of accumulation mode aerosols?

A

100-1000nm

48
Q

What is the diameter of coarse mode aerosols?

A

1000-10000nm

49
Q

Where are Aitken mode concentrations highest?

A

Over land regions with strong SO2 emissions

50
Q

What is the spatial distribution of accumulation mode related to?

A

Closely related to the anthropogenic emissions in the climate model

51
Q

Where does coarse mode have the highest conc?

A

In regions of dust and sea salt particles

52
Q

How do aerosol distributions vary?

A

Seasonally and regionally

53
Q

What are aerosol modes tightly coupled with?

A

Aerosol formation pathways

54
Q

What are aerosol size distributions controlled by?

A

Prevailing aerosol sources and sinks during transport

55
Q

Why are physical properties of aerosols important to understand?

A

Important if we wish to describe in climate models how particles interact with clouds and radiation

56
Q

What does cloud droplet number depend on? (3 things)

A

-particle numbers and sizes
-cloud dynamics
-particle chemical composition

57
Q

What is DMPS and what is it used for?

A

DMPS=differential mobility particle sizer
Used for measuring the aerosol size distribution

58
Q

How can we compare models with different channel resolutions?

A

We can normalise by bin size

59
Q

What is the number per cm3 of aerosols for urban environment?

A

105 -106 cm-3

60
Q

What is the number per cm3 of aerosols for rural continental environment?

A

2000-10000 cm-3

61
Q

What is the number per cm3 of aerosols for remote continental environment?

A

1000-10000 cm-3

62
Q

What is the number per cm3 of aerosols for marine environment?

A

100-400 cm-3

63
Q

What is the dominant source of aerosols for an urban environment?

A

Dominated by emissions
Includes primary particulate emissions from industries, transport, power generation

64
Q

What size aerosol particle dominates the urban environment

A

Dominated by ultra fine particle Dp <0.10 micron, but this varies depending on the proximity to sources and prevailing meteorology

65
Q

What are the two main modes for mass distribution in urban environment?

A

Accumulation and coarse

66
Q

What is the main source of rural continental aerosols?

A

Mainly natural with moderate anthropogenic influence

67
Q

What are the dominating mass mode of aerosols for rural continental environment?

A

Coarse mode

68
Q

What is the main source of aerosols in the remote continental environment?

A

Natural primary particles e.g. dust, pollens, secondary oxidation products

69
Q

What are the two dominating modes for aerosol number?

A

Nucleation and accumulation

70
Q

In rural continental environment, what do particles smaller than 2.5 microns consist of?

A

Sulfate, ammonium and organics

71
Q

What is the main source of aerosols for marine environments?

A

Primary production or sea-salt aerosol particles from bubble-bursting from breaking waves

72
Q

What is the main mode for Aerosol mass distribution for a marine environment?

A

Coarse mode

73
Q

What causes the seasonal cycle in aerosols in marine environments?

A

Meteorology/biology (e.g. algae)

74
Q

What is the main source of aerosol emissions in a desert environment?

A

Desert dust but strongly dependent on wind velocity

75
Q

How do dust storms affect aerosol particles cross-continentally?

A

Individual dust storms can transfer smaller desert particles <10 microns from Africa over oceans to Amazon rainforest

76
Q

Why is the accumulation mode of aerosols typically higher in free troposphere rather than lower troposphere?

A

No precipitation scavenging by clouds

77
Q

What mode is often present in free troposphere environment and why?

A

Nucleation mode often present as conditions suitable for second age aerosol formation

78
Q

What are the poles like in regards to aerosol conc

A

-Very low no. Conc
-strong seasonal cycle in aerosol size distribution

Aerosols, Clouds, Atmospheres (12 decks)

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