LEC.173 Biogeochemical Cycles Flashcards
Why is the atmosphere in dynamic disequilibrium/non-steady state?
Anthropogenic inputs > outputs
What drives most gaseous chemical reactions in the atmosphere, what is the common intermediate of indirect reactions, and why?
Sunlight, OH, very reactive and short half life
What 2 things are interchangeable?
Energy and mass
What does sunlight emit energy as?
Electromagnetic radiation of different wavelengths (specific wavelengths absorbed by matter in atmosphere)
What are the 3 different groupings of UV and what are their ranges in wavelength?
- UVA (greatest skin penetration) = 100 - 280 nm
- UVB (skin burn) = 280 - 315 nm
- UVC = 315 - 400 nm
Which part of the atmosphere has a high concentration of ozone, what is ozone formed by, and what wavelengths of radiation is ozone capable of absorbing?
Stratosphere, photolysis of oxygen, 300nm (harmful radiation)
What is energy proportional to and what is it inversely proportional to?
Proportional to frequency of light, inversely proportional to wavelength (shorter wavelength = higher energy)
What is the Chapman cycle?
Formation and destruction of ozone (continuously regenerated by UV radiation)
Which 3 things other than UV can break down ozone?
- NO
- OH radicals
- Cl radicals from CFCs
When was the Montreal Protocol introduced and what did it do?
1987, regulates production/consumption of CFCs
What currently has a small but increasing threat on ozone?
Dichloromethane (useful as a solvent in labs)
What is a medium for many chemical reactions in the atmosphere, where is most liquid water in the atmosphere, and what % cloud cover is there globally?
Liquid water, near bottom due to temp. and pressure profile so affects surface vegetation, 50%
Put in order from smallest to largest: large cloud drop, typical raindrop, condensation nuclei
Condensation nuclei –> large cloud drop –> typical raindrop
What is the 6 step process of reactions taking place in cloud droplets?
- Turbulent diffusion through gas phase towards droplet
- Molecular diffusion through thin layer of laminar air surrounding droplet
- Adsorption at surface
- Molecular diffusion (absorption) into + through liquid
- Chemical reaction
- Transport of product out of droplet (results in deposition via scavenging + washout)
What type of particles in cloud drops can act as a reactant or catalytic surface?
Aerosol particles
What are 4 ways that cloud droplets promote chemical reactions?
- Some gases highly soluble (enter into water droplets where may be more reactive in gas phase)
- Solutes may be ionised in water
- Water hydrolyses some solutes
- Brings together substances that would otherwise be separated (soluble gases + aerosol ions)
How much more SO2 emissions are produced by coal burning than oxidation of natural sulfur?
2x more (important in acid rain formation)
Why are SO2 reactions faster in the aqueous cloud phase?
Normally slow but catalysed by Fe and Mn salts
What are the 2 types of acid deposition from clouds?
- Wet (e.g. precipitation)
- Dry
What are the 2 reasons that deposition from clouds involves different physical/chemical processes?
- Material properties (particle size, gas solubility/lifetime/reaction in aqueous phase)
- Location + meteorology (cloud frequency, rainfall rate, surface type)
Where in the UK is there the most dry and wet sulfur deposition?
Dry: At regions of high sulfur conc. (specific)
Wet: Along patterns of precipitation across UK
Which region of the UK has the most acidic rain and why?
North East, predominant wind direction from Atlantic/South West so westerlies carry acidic rain North East
Why do rocks react with acid rain and therefore weather at the Earth’s surface?
Igneous/metamorphic/some sedimentary rocks form at high temp. and pressure and low O2 conc. so thermodynamically unstable at Earth’s surface
What are the 4 main weathering components?
- H2O
- O2
- H+ due to CO2 and hence H2CO3 (acid rain)
- DOM (Dissolved Organic Matter)
How can acid rain disrupt Na and K channels in aquatic life?
Can cause release of metal ions which bind with essential nutrients
What 3 things do weathering rates depend on?
- Environmental factors e.g. temp
- Mineral assemblages
- Degree of instability in system
What are the 4 chemical weathering reactions?
- Dissolution
- Hydrolysis
- Acid-base reactions
- Redox reactions
What are 2 examples of dissolution chemical weathering reactions?
- CaCO3 (one of fastest, water = medium but not directly involved)
- Apatite (biological productivity of oceans controlled by phosphorus - related to global weathering of apatite)
What are the 2 types of hydrolysis chemical weathering reactions?
- Incongruent: partial breakdown e.g. produces secondary mineral
- Congruent: produces whole range of basic ion constituent components
What do acid-base chemical weathering reactions (global acid-base titration) consume and produce?
Consume: H+
Produce: Alkalinity
What is alkalinity a measure of?
Acid neutralisation capacity
Why are redox chemical weathering reactions important?
Fe(III) oxides common at Earth’s surface –> form H+ which increases acidity (can harm aquatic ecosystems)
What are the 2 dominant species in fresh water?
- Bicarbonate (HCO3-)
- Calcium (Ca2+)
Why is Ca2+ in fresh water important?
Has an impact on pH, alkalinity, and water hardness
What are 4 globally significant effects of weathering?
- Affects atmospheric CO2
- One of 2 major contributors to soil development (other is organic matter)
- Affects water quality (has biological impacts e.g. nutrients)
- Creates economic mineral deposits
What are the 6 processes in the geological carbon cycle affecting p(CO2)?
- Air-water equilibrium of CO2
- Carbonate weathering
- Silicate weathering
- Carbonate precipitation + burial in oceans
- Igneous/metamorphic degassing
- Organic matter burial in sediments
Which of the 6 processes in the geological carbon cycle increase/decrease CO2?
Increase: Carbonate weathering, carbonate ppt. + burial in oceans, + igenous/metamorphic degassing
Decrease: Silicate weathering, organic matter burial in sediments
What are C4 plants and where are they most efficient?
Produce 4C compounds, tropical climates e.g. sugarcane
What are C3 plants and what do they utilise?
Produce 3C compounds, utilise Rubisco enzyme in Calvin cycle
Define autotroph
Utilises inorganic C sources e.g. CO2 and HCO3-
Define heterotroph
Utilises organic C sources (very important, diverse organisms)
What is the equation for anoxygenic photosynthesis (evolved before organic photosynthesis)?
6CO2 + 12H2S (source of e-) + hv –> C6H12O6 + 12S + 6H2O
Define chemoautotroph
Inorganic C source independent of light (gets energy from oxidising reduced inorganic compounds), important in soils/sediments/hydrothermal vents, mainly bacteria/archaea, e.g. nitrification
What are 4 processes that involve the transfer of electrons from reduced C to an electron acceptor?
- Aerobic respiration
- Anaerobic respiration
- Fermentation
- Methanogenesis
Describe aerobic respiration
O2 is the terminal electron acceptor, is the preferred energy-yielding reaction as has maximum energy yield per mol of glucose
Describe anaerobic respiration
Various terminal electron acceptors, occupy hypoxic/suboxic/anoxic environments
Describe fermentation
Anaerobic, energy-yielding reaction involving redox changes to C in large organic molecules but with no terminal electron acceptor
Describe methanogenesis
CH4 produced, archaea (e.g. in digestive tract of cows)
What is the Earth’s biogenic disequilibrium caused by?
Coexistence of N2, O2, and liquid water instead of more stable nitrate
How is CH3Hg+ formed and which highly toxic disease did it cause in Japan in the 1950s?
Formed microbially under anaerobic conditions, Minamata disease (was released in industrial wastewaters –> bioaccumulation in shellfish)
What form of Hg (mercury) has a long residence time in the atmosphere?
Hg(0)
What did the Minamata Convention do?
Banned new Hg mines and phased out existing ones, phased out Hg use in products/processes, controlled measures on emissions to air and on releases to land/water
What are most Hg emissions produced by?
Fossil fuel combustion
Where are 10% of global annual Hg emissions to the atmosphere deposited?
Arctic (increasing)
