Aerosol forcing

Question 1

What is radiative forcing?

Answer 1

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

Question 2

How will CO2 change in the future?

Answer 2

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

Question 3

What is an aerosol?

Answer 3

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

Question 4

What makes up aerosols?

Answer 4

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

Question 5

Where do aerosols come from?

Answer 5

• industry
• volcanoes (natural)
• fertilisers
• diesel fuel
• turpines

Question 6

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

Answer 6

800,000

Question 7

How much soot is produced from biomass burning per year?

Answer 7

54 Tg

Question 8

How much industrial dust is emitted every year?

Answer 8

100 Tg

Question 9

How much anthropogenic sulphate is emitted each year?

Answer 9

200 Tg

Question 10

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

Answer 10

16-500 Tg

Question 11

Where are aerosols generated?

Answer 11

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

Question 12

Which two ways can be classify aerosols?

Answer 12

Primary and Secondary

Question 13

What is a primary aerosol?

Answer 13

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

Question 14

What is a secondary aerosol?

Answer 14

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

Question 15

What does volatile mean?

Answer 15

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

Question 16

What two ways are aerosols removed?

Answer 16

Dry and wet processes

Question 17

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

Answer 17

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

Question 18

What is aerosol mass important for?

Answer 18

Light scattering

Question 19

What is aerosol number important for?

Answer 19

Effect on clouds (CCN)

Question 20

How does aerosol mass differ?

Answer 20

Bulk concentration near emission source

Question 21

How does aerosol number differ?

Answer 21

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

Question 22

What is the annual mean mass of PM2.5?

Answer 22

1-100 µg m-3

Question 23

What is the annual mean surface particle number?

Answer 23

100-10,000 particles m-3

Question 24

What model predicts annual mean surface particle number?

Answer 24

GLOMAP global aerosol model

Question 25

What satellites predicts annual mean mass of PM2.5?

Answer 25

MODIS satellite

Question 26

Where does anthropogenic sulphate originate from?

Answer 26

Burning fossil fuels, Volcanoes and Phytoplankton

Question 27

How does burning fossil fuels generate sulphate aerosol?

Answer 27

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

Question 28

What is one direct aerosol effect?

Answer 28

Scattering and absorption of solar radiation

Question 29

What is one indirect aerosol effect?

Answer 29

Changes in cloud properties

Question 30

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

Answer 30

Short wave radiation

Question 31

Scattering efficiency of aerosols depends on ...

Answer 31

- size (distribution of particle) - composition (refractive index) - shape of particle

Question 32

Absorption efficiency of aerosols depends on ...

Answer 32

- mass of absorbing material | - compositions (mixing of absorber and scatterer)

Question 33

What effect does light scattering aerosol have?

Answer 33

Atmosphere and surface cools

Question 34

What effect does light absorbing aerosol have?

Answer 34

Atmosphere warms and surface cools

Question 35

What is the single-scattering albedo (SSA)?

Answer 35

A measure of the relative amount of light scattered and absorbed

Question 36

What is the average SSA for northern hemisphere aerosol?

Answer 36

˜0.85-0.95

Question 37

If SSA > 0.95 ...

Answer 37

Net negative top of atmosphere (TOA) forcing

Question 38

If SSA < 0.85 ...

Answer 38

Net positive top of atmosphere (TOA) forcing

Question 39

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

Answer 39

0.2 therefore it absorbs

Question 40

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

Answer 40

1.0 therefore it scatters

Question 41

How is SSA calculated?

Answer 41

Scattering/(scattering+absorption)

Question 42

What is the net cooling effect of clouds?

Answer 42

27 Wm^-2

Question 43

Clouds and the aerosol indirect effect ...

Answer 43

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)

Question 44

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

Answer 44

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

Question 45

What albedo do clouds have?

Answer 45

Very variable: 0.1-0.8

Question 46

What causes a change in cloud albedo?

Answer 46

A change in cloud droplet number

Question 47

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

Answer 47

∆A/A = (1-A) (∆N/N)

Question 48

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

Answer 48

Changes by 0.5%

Question 49

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

Answer 49

Decreased up to the 1980s then began to rise again

Question 50

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

Answer 50

EU legislation on aerosol pollution

Question 51

What uncertainties are associated with the aerosol indirect effect?

Answer 51

- highly variable clouds - response of clouds to droplet number is poorly understood - hard to link changes to changes in aerosol

Question 52

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

Answer 52

-2 Wm^-2