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Climate Change > Aerosol forcing > Flashcards

Aerosol forcing Flashcards

1
Q

What is radiative forcing?

A

The change in net irradiance at the tropopause with surface and tropospheric temperatures held fixed (positive values imply a heating of the troposphere)

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2
Q

How will CO2 change in the future?

A

Considerable uncertainty, don’t know how it will evolve in the future

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3
Q

What is an aerosol?

A

Suspension of tiny particles in the air, with a diameter between 0.01-10 micrometers

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4
Q

What makes up aerosols?

A

Sulfates, nitrates, organic compounds, metals, dust, sea salt …

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5
Q

Where do aerosols come from?

A
  • industry
  • volcanoes (natural)
  • fertilisers
  • diesel fuel
  • turpines
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6
Q

How many people does EU legislation on aerosols save per year?

A

800,000

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7
Q

How much soot is produced from biomass burning per year?

A

54 Tg

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8
Q

How much industrial dust is emitted every year?

A

100 Tg

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9
Q

How much anthropogenic sulphate is emitted each year?

A

200 Tg

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10
Q

How much biogenic volatile organic carbon (VOC) is emitted every year?

A

16-500 Tg

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11
Q

Where are aerosols generated?

A
  • over industry
  • natural: forest fires, dust etc.
  • overall, anywhere outside of the poles, aerosol is being generated
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12
Q

Which two ways can be classify aerosols?

A

Primary and Secondary

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13
Q

What is a primary aerosol?

A

An aerosol that is directly emitted to the atmosphere e.g. sea salt

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14
Q

What is a secondary aerosol?

A

Originate from gases which then oxidise or nucleate to form the secondary aerosol (important for cloud formation)

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15
Q

What does volatile mean?

A

Easily evaporated (less volatile means something is more likely to condense)

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16
Q

What two ways are aerosols removed?

A

Dry and wet processes

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17
Q

How does lifetime of aerosols change if they reach the stratosphere?

A

Longer life time e.g. after volcanic eruptions, can remain for a few years

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18
Q

What is aerosol mass important for?

A

Light scattering

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19
Q

What is aerosol number important for?

A

Effect on clouds (CCN)

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20
Q

How does aerosol mass differ?

A

Bulk concentration near emission source

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21
Q

How does aerosol number differ?

A

Homogenised, reasonable spread (secondary aerosols are able to form further away from source)

22
Q

What is the annual mean mass of PM2.5?

A

1-100 µg m-3

23
Q

What is the annual mean surface particle number?

A

100-10,000 particles m-3

24
Q

What model predicts annual mean surface particle number?

A

GLOMAP global aerosol model

25
Q

What satellites predicts annual mean mass of PM2.5?

A

MODIS satellite

26
Q

Where does anthropogenic sulphate originate from?

A

Burning fossil fuels, Volcanoes and Phytoplankton

27
Q

How does burning fossil fuels generate sulphate aerosol?

A

SO2 and CO2 oxidises to Sulphuric acid (H2SO4) which nucleated and condenses to Sulfate aerosol

28
Q

What is one direct aerosol effect?

A

Scattering and absorption of solar radiation

29
Q

What is one indirect aerosol effect?

A

Changes in cloud properties

30
Q

Which band of the EM spectrum does aerosol forcing mostly affect?

A

Short wave radiation

31
Q

Scattering efficiency of aerosols depends on …

A
  • size (distribution of particle)
  • composition (refractive index)
  • shape of particle
32
Q

Absorption efficiency of aerosols depends on …

A
  • mass of absorbing material

- compositions (mixing of absorber and scatterer)

33
Q

What effect does light scattering aerosol have?

A

Atmosphere and surface cools

34
Q

What effect does light absorbing aerosol have?

A

Atmosphere warms and surface cools

35
Q

What is the single-scattering albedo (SSA)?

A

A measure of the relative amount of light scattered and absorbed

36
Q

What is the average SSA for northern hemisphere aerosol?

A

˜0.85-0.95

37
Q

If SSA > 0.95 …

A

Net negative top of atmosphere (TOA) forcing

38
Q

If SSA < 0.85 …

A

Net positive top of atmosphere (TOA) forcing

39
Q

What is the SSA for black carbon and therefore does it scatter or absorb?

A

0.2 therefore it absorbs

40
Q

What is the SSA for sulphate aerosol and therefore does it scatter or absorb?

A

1.0 therefore it scatters

41
Q

How is SSA calculated?

A

Scattering/(scattering+absorption)

42
Q

What is the net cooling effect of clouds?

A

27 Wm^-2

43
Q

Clouds and the aerosol indirect effect …

A

More aerosol particles… more smaller cloud droplets… clouds more reflective and cool climate (1st effect) … smaller cloud drops take longer to form rain=increased cloud lifetime (2nd effect)

44
Q

What evidence do ship tracks provide for the aerosol indirect effect?

A

Pollution from ship … more aerosol … more smaller cloud droplets … cloud more reflective (increased albedo)
-clouds form over ship tracks

45
Q

What albedo do clouds have?

A

Very variable: 0.1-0.8

46
Q

What causes a change in cloud albedo?

A

A change in cloud droplet number

47
Q

How can we approximate cloud albedo (A) due to change in cloud droplet number (N)?

A

∆A/A = (1-A) (∆N/N)

48
Q

How much does cloud albedo change by due to a change of 1% in cloud droplet number?

A

Changes by 0.5%

49
Q

How has pattern of the amount of radiation reaching the Earths surface changed?

A

Decreased up to the 1980s then began to rise again

50
Q

What is one possible reason for the rise in radiation reaching the earths surface since the 1980s?

A

EU legislation on aerosol pollution

51
Q

What uncertainties are associated with the aerosol indirect effect?

A
  • highly variable clouds
  • response of clouds to droplet number is poorly understood
  • hard to link changes to changes in aerosol
52
Q

Roughly, what is the globally averaged radiative forcing due to all aerosol effects over the industrial period?

A

-2 Wm^-2

Climate Change (13 decks)

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