3.3 - Greenhouse Gas Emissions Flashcards
What is the atmospheric lifetime of methane and how does it compare to N2O?
Methane has an atmospheric lifetime of 12 years, while N2O has a much longer lifetime of 114 years. This means N2O has more prolonged effects in the atmosphere.
What is the global warming potential of methane and N2O on a 100-year basis?
Methane has a GWP of 23 (1kg of methane = 23kg of CO2), while N2O has a GWP of 296, making it a much more potent greenhouse gas.
this means that 1kg of methane has the same impact as 23kg of CO2
Why have CFCs been phased out and what are they replaced with?
Answer: CFCs have been phased out because they deplete the ozone layer. They have been replaced with HFCs, which don’t deplete ozone but are still potent greenhouse gases.
Sources of methane
- Natural: wetlands, termites, ocean
- Agricultural: rice cultivation, ruminant animals
- Human activities: biomass burning, natural gas extraction/transport, landfills
Removal Process of Methane
- Chemical destruction: CH4 + OH → CH3 + H2O
- Soil absorption
- Stratospheric chemical reaction
Nitrous Oxide (N2O)’s contribution to anthropogenic greenhouse effect
6%
Sources of N2O
- Natural: microbiological processes in soil (e.g. wet forests) and oceans
- Human activities:
- Biomass burning
- Industrial processes
- Agricultural soils (N fertilizer)
- Cattle and feedlots
- Automobile catalytic converters (minor impact)
Removal of N2O
- Primary mechanism: photolysis in stratosphere (N2O + UV → N2 + O)
- however this process is slow, and only some reaches the stratosphere and the rest stays in the troposphere as a greenhouse gas
Categories of Halogenated Hydrocarbons
Categories: CFCs, HCFCs, HFCs
Effects of Halogenated Hydrocarbons
- Direct: Strong greenhouse gases
- Indirect: CFCs (and to a lower extent HCFCs) deplete stratospheric ozone
- HFCs (CFC/HCFC substitutes) are potent greenhouse gases
- Long atmospheric lifetime due to low chemical reactivity
Removal of Halogenated Hydrocarbons
- Photo-dissociation - photolysis; how halocarbons break apart due to UV in the stratosphere
- Chemical removal
What are aerosols and how are they formed?
Liquid or solid particles (10nm to 10m) suspended in air
- Formation through:
- Nucleation from gaseous precursors (condensation of oversaturated steam)
- H2SO4 (sulfur acid) originates from SO2 emissions
- Wind mobilization (soil dust, sea salt)
What is the overall cooling effect of aerosols?
- however different aerosols have varying effects and some contribute to warming rather than cooling
- can mask greenhouse gas warming effects
Atmospheric lifetime of aerosols
Short
What are the two main effects of aerosols on climate?
- Direct effect: Scatters/absorbs solar and infrared radiation
- Indirect effect: Affects cloud properties (though quantitative data is limited)
Which greenhouse gases are addressed by the Kyoto Protocol?
Answer: The Kyoto Protocol addresses:
- CO2
- CH4
- N2O
- PFCs (CF4, C2F6)
- SF6
- HFCs
GHGs addressed in Montreal Protocol
- CFCs
- HCFCs
Radiation Budget
radiation budget (or energy budget) → balance between incoming and outgoing radiation in Earth’s climate system
What happens where there is a balance or imbalance in the radiation budget?
- when balanced → Earth’s average temperature remains stable
- disrupted by greenhouse gases
- imbalance can lead to warming (if more energy is retained than lost) or cooling (when more energy is lost than retained)
What GHGs have a high effect on radiative budget?
- CO2, CH4, N2O → very high effects on radiative budget
- Ozone → high effects
- Aerosols → cloud interactions have low effect, but radiation interactions have high/medium effects
