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SOEE3760 > Atmospheric Composition > Flashcards

Atmospheric Composition Flashcards

1
Q

What are BVOCs, and what are the main types?

A

Biogenic Volartile Organic Compounds - emitted into atmosphere by vegetation - mostly trees

  • Isoprenes - 5C atoms - ~500 TgC/year
  • Monoterpenes - 2Xisoprene (10C atoms) - ~100 TgC/year
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2
Q

Why are BVOCs emitted by vegetation?

A

Takes a lot of energy to synthesise BVOCs - so why?
- Defense from insect / herbivore attack
- Enhancing resilience to environmental stress
- Inhibiting establishment of competing plants

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3
Q

How are the different BVOCs emitted/stored?

A
  • Monoterpenes - stored in leaf as liquids - when is warm enough (temperature dependent) - they vapourise and are released
  • Isoprenes - synthesised in leaves and emitted straight away - more linked to rate of photosynthesis
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4
Q

Explain the proportion of global contributions to BVOCs

A
  • Mainly tropical forests - small amount from temperate and boreal forests
  • Small amount from biomass burning and marine ecosystems
  • But is very hard to know exactly how much is emitted - so need to base on emission algorithms
  • Compounds are being emitted when hottest and sunniest - monoterpenes are more geographically spread
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5
Q

How do BVOCs affect the atmosphere?

A
  • One emitted - react with oxidants in atmosphere - e.g., ozone/OH - and form more complicated oxidised compounds - Biogenic Secondary Organic Aerosol (SOA)
  • These oxidised compounds form condensation products - start at nano-scale but can get larger
  • These oxidation reactions reduce their volatility - making them more inclined to condense onto particles in the atmosphere
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6
Q

What happens if BVOCs form large and soluble compounds in the atmosphere?

A

If big enough and soluble enough - these compounds can act as cloud droplets = more droplets = cloud reflects more radiation = higher albedo = cause a net cooling

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7
Q

What happens when BVOCs react with OH radicals?

A

OH reacts with methane (greenhouse gas) - OH removes methane from atmosphere by oxidising it
- So if BVOCs are released and react with OH - depleting the amount of OH in atmosphere - the atmospheric lifetime of methane (CH4) increases - potentially causing warming

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8
Q

How can BVOCs react with ozone?

A

BVOCs can directly react with ozone (O3) - reducing its concentration
- BUT - BVOCs are also involved in the formation of O3 in the troposphere - increaseing its concentration
- So net impact of emission is to create more ozone - potentially causing warming

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9
Q

Explain the two competing effects of BVOCs being emitted into the atmosphere

A
  • Cooling - due to more/large particle formation and brighter more reflective clouds
  • Warming - due to increase in methane and ozone (greenhouse gases)
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10
Q

What is the impact of global deforestation on short-lived climate factors?

A
  • Positive radiative effect (warming) - due to reduction in aerosol formation = lower reflectivity of clouds
  • Negative radiative effect (cooling) due to reduction in GHG - ozone and methane
  • But net effect - from short-lived climate factors is a warming effect due to deforestation
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11
Q

How will increases in temperature create a natural aerosol-climate feedback?

A
  • Higher temperature = higher BVOC emissions = brigher clouds = higher albedo = cooling effect (negative aerosol feedback)
  • Fires have similar effect - release more of these compounds into atmosphere
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12
Q

What did Paasonen et al., 2013 and Yli-Juuti et al., 2021 find out about temperature and particle number/mass?

A

Paasonen et al., 2013:
- Used N100 - number of particles with diameter larger than 100nm - using mobility particle size spectometers
- Found strong relationship between temperature and particle number across 11 sites

Yli-Juuti et al., 2021:
- Found strong relationship between temperature and organic aerosol mass in boreal forest
- Showed that they also found brigher clouds in these regions due to increased temperature and therefore more aerosols

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13
Q

How is change in aerosol mass affected by temperature in boreal vs tropical forests?

A
  • Blichner et al., 2024:
  • Boreal forest - strong positive relationship between organic aerosol mass per change in temperature
  • Amazon rainforest - models were much more varied - far away from understanding the feedback here
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14
Q

How does ozone vary depending on its position in atmosphere?

A

O + O2 = O3
- Lots of naturally produced O3 in stratosphere
- High energy sunlight needed
- O3 is produced in situ in troposphere from both natural and anthropogenic precursors
- O3 at surface is harmful to human health and vegetation

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15
Q

How is O3 taken up by vegetation?

A
  • O3 is efficiently taken up by plants via their stomata
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16
Q

How does O3 in leaves affect processes within the leaf?

A
  • Exposure to O3 will directly modify (reduce) stomatal conductance
  • O3 damage also reduces carbon fixation via photosynthesis
  • Can reduce rates of photosynthesis and transpiration
17
Q

How do changes in CO2 affect ozone in the atmosphere?

A
  • Increasing CO2 levels cause a decrease in stomatal conductance (gs) - to try and preserve relative conc of CO2 inside and outside the leaf
  • If this happens - we would expect the dry deposition of O3 to decrease - therefore we would expect to see an increase in O3 conc
  • Important in terms of air quality
18
Q

How can O3 damage plants?

A
  • Ozone can inhibit photosynthesis and reduce stomatal conductance (gs)
  • But we don’t know how sensitive vegetation is to O3 damage - so we dont know how much it has affected land carbon sink sequestration
19
Q

How does ozone affect gs and photosynthesis? (including recent findings)

A

Lombardozzi et al., 2012
- Showed that high O3 can alter stomatal conductance (gs) independent of photosynthesis rates - i.e. response of photosynthesis and gs to ozone are decoupled
- Suggests we may be over-predicting the O3 damage on gs

Modelling:
- Big changes in transpiration when gs and photosynthesis coupled
- Small changes to transpiration when gs and photosynthesis not coupled

20
Q

Given a reduction isoprene concentration in the atmosphere, explain some of the potential positive and negative feedbacks caused by ozone at different NOx concentrations

A

Increase O3 = decrease photosynthesis = decrease isoprenes:
- high NOx = reduction in surface O3 - negative feedback OR low NOx = increase surface O3 - positive feedback

21
Q

What knock-on impact can ozone damage have on heat fluxes?

A
  • Increase O3 damage = decrease transpiration = reduction in latent heat flux
  • So O3 damage will lead to increase in sensible heat flux
  • Swicthes proportions of fluxes
  • Also- Arnold et al., 2018: decreased transpiration = decrease humidity = decrease cloud cover = increase SW radiation at surface (less reflected by clouds) = increase in surface temp

SOEE3760 (12 decks)

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