Topic 6

Atmospheric systems

atmosphere

a dynamic system of inputs, outputs, storages and flows

\
the air - the zones between the lithosphere and space (about 1,100km deep)

current atmospheric composition

21% oxygen

78% nitrogen

0\.04% carbon dioxide

troposphere

the atmosphere from 0km to 10km above sea level

stratosphere

the atmosphere from 10km to 50km above sea level

bubbles trapped in ice

a way of measuring atmospheric conditions in the past - looking at composition of the trapped air

the greenhouse effect

a natural and necessary phenomenon maintaining suitable temperatures for life on Earth

light from the sun passes through the atmosphere > 50% is absorbed > the Earth heats up > infrared heat is radiated from Earth > greenhouse gases reflect this heat back to Earth

greenhouse gases (GHG)

water vapour, carbon dioxide and methane \= the main ones

stratospheric ozone

a key component of the atmosphere which provides protection for living things from UV radiation from the sun - aka "the ozone layer"

ozone

O3 - found in two layers:

GOOD - the stratosphere

BAD - the troposphere

ultraviolet radiation (UV) effects on life

• genetic mutation and subsequent effects on health

• damage to living tissue

• cataract formation on eyes

• skin cancer

• suppression of the immune system

• damage to photosynthetic organisms, especially phytoplankton

• damage to consumers of photosynthetic organisms, especially zooplankton

ultraviolet radiation (UV) benefits

• stimulates the production of vitamin D

• can be used to treat psoriasis and vitiligo (skin diseases)

• use as a steriliser and purifier as it kills pathogenic (disease causing) bacteria

ozone-depleting substance (ODS)

All these substances contribute to the reduction of stratospheric ozonne:

• chloroflourocarbons (CFCs or freons) --> found in spray cans and refrigerants --> release chlorine atoms

• hydrochloroflourocarbons (HCFCs) --> as an alternative to CFCs --> release chlorine atoms, but shorter lifespan in the atmosphere (but also stronger greenhouse effect)

• halons --> fire extinguishers --> release bromine atoms

• methyl bromide --> pesticide --> releases bromine atoms

• nitrogen oxides (NOx) --> from bacterial breakdown of fertilisers and high flying aircraft --> NO reacts with ozone

reducing ODS (altering human activity producing pollution)

• replace gas-blown plastics

• replace CFCs with carbon dioxide, propane or air as a propellant

• replace aerosols with pump action sprays

• replace methyl bromide pesticides

HOWEVER, most CFC replacements are greenhouse gases

reducing ODS (regulating and reducing the pollutants at the source)

• recover and recyle CFCs from refrigerants and AC units

• legislate to have fridges returned to the manufacturer and coolants removed and stored

• capture CFCs from scrap car air conditioner units

reducing ODC (clean up and restoration)

- add ozone to or remove chlorine from the stratosphere - not practical but has been suggested that ozone filled balloons be released

the Montreal Protocol (outline)

an international agreement made by the UN made to phase out the production of ODS in 1987

since 1987, it has been strengthened by 7 amendments (e.g. LEDCs had more time to phase out ODS than MEDCs)

197 countries ratified the agreement = the first universally ratified UN agreement

the Montreal Protocol (significance)

1. best example of international cooperation on an environmental issue

2. an example of the precautionary principle in science-based decision making

3. an example of many experts in their field coming together to research the problem and find a solution

4. the first to recognise that different countries could phase-out ODS at different rates according to their economic status

5. the first with regulations that were carefully monitored

the Montreal Protocol (effects)

there is a clear trend in reduction of ODS since the Montreal Protocol:

total ODS consumption was at =

• 41,500,000 tonnes in 1986

• 19,000,000 tonnes in 1992

• less than 1,500,000 tonnnes since 2000

however, due to the long life of CFCs in the atmosphere, the peak ODS level was in 2005, and will not reach pre-ODS levels until around 2050

primary pollutants

emitted directly from a process - may be natural (e.g. volcanoes) or anthropogenic (human made, e.g. industry, motor vehicles)

fossil fuel combustion

a major source of anthropogenic primary pollution - produces:

• carbon monoxide

• carbon dioxide

• unburned hydrocarbons

• nitrogen oxides

• sulphur dioxide

• particulates/particulate matter (PM)

secondary pollution

formed when primary pollutants undergo a variety of reactions with other chemicals already in the atmosphere

photochemical reaction

the formation of secondary pollution in the presence of sunlight

e.g. tropospheric ozone, particulates produced from gaseous primary pollutants, peroxyacetyl nitrate (PAN)

tropospheric ozone (formation)

10% of ozone is found here

formed by the splitting of nitrous oxides in the presence of sunlight providing an extra oxygen atom to bond with O2 forming O3

tropospheric ozone (effects)

• ozone is a toxic gas with high oxidation potential

• damage to plants --> ozone is absorbed by plants and reacts with chlorophyll = reduction in productivity

• damage to humans --> at even low concentrations ozone can reduce the actions of the lungs and acts as an eye irritant

• damage to materials and products --> ozone attacks natural rubber, cellulose and some plastics; reduces the lifespan of car tires; bleaches fabrics

particulates (formation)

the particles of carbon and other substances caused by burning any organic substance or fossil fuel - often PM10 because smaller than 10 micrometeres in diameter

e.g. energy production burning fossil fuels; poorly maintained diesel engines release large amounts

particulates (dangers)

• they cannot be filtered out by our respiratory system (nose, throat and lungs) and so stay in our bodies

• asthma causing

• many are carcinogenic (cancer-causing)

• in areas close to industrial regions, crops may become coated with particulates - causes a reduction in productivity as the amount of light penetrating leaves decreases

photochemical smog

mainly nitrogen dioxide and ozone, but is a complex mixture of 100 different primary and secondary pollutants - created due to this mixture and action from the sun

often worst in large cities which are low-lying and/or in valleys

thermal inversion

when a warm layer of air sits over a layer of cooler air preventing the lower layer of air from rising - often contributes to increased photochemical smog formation

reducing urban air pollution (altering human activity producing pollution)

• consume less, burn less fossil fuel - especially in internal combustion engines (cars, planes etc)

• act as informed consumers and purchase energy efficient technologies

• lobby governments to increase renewable energy use

reducing urban air pollution (regulating and reducing the pollutants at the point of source)

• government regulation/tax

• catalytic converters to clean exhaust of primary pollutants from car exhausts

• fuel quality may be regulated by governments

reducing urban air pollution (clean up and restoration)

• afforestation to increase carbon sinks and filter air (but does not reduce emissions)

• re-greening of cities --> more trees, parks = absorbs carbon dioxide

acid deposition

acid coming down from the air

wet deposition

acid deposition in the form of rain or snow

dry deposition

acid deposition in the form of ash or dry particles

acid deposition pollutants

primary - sulphur dioxides and nitrogen oxides

these react with water to create sulphuric and nitric acids

acid deposition effects (coniferous forests)

• yellowing of leaves and buds as chlorophyll is lost

• reduced growth in the forest --> leads nutrients being washed away and pathogens to gain entry

• symbiotic root microbes are killed --> reduces the availability of nutrients

• reduces ability of soil particles to hold onto nutrients (e.g. calcium, magnesium and potassium)

• releases toxic aluminium ions from soil particles which damage roots

acid deposition effects (aluminium ions on aquatic organisms)

aluminium is a common element in the soil, but acid precipitation increases its solubility

• Al ends up in rivers and streams through leaching

• fish are very sensitive to Al in water as it affects their oxygen and salt regulation

acid deposition effects (lichens)

symbiotic pairing of and alga and fungi - found on trees and buildings

particularly sensitive to gaseous pollutants such as sulphur dioxide - therefore a useful indirect measure of pollution (indicator species)

reduction of acid deposition (altering human activity producing pollution)

• replace fossil fuel use by alternatives: ethanol to run cars, renewable energy sources for electricity

• reduce overall demand for electricity: education campaigns to turn off lights and insulate houses

• use less private transport - more public, more cycling and walking

• use low sulphur fuels

EVALUATION

• also reduces CO2, but we still live in a fossil fuel reliant society

• demand for power is increasing, especially in China and India

reduction of acid deposition (regulating and reducing the pollutants at the point of source)

• clean-up technologies at 'end of pipe' locations [point of emission]. e.g. scrubbing in chimneys to remove sulphur dioxide

• catalytic converters convert nitrous oxides back into nitrogen

EVALUATION

• expensive and costs passed on to consumers

• catalysers are cost effective if maintained, but are expensive to buy

reduction of acid deposition (clean up and restoration)

• liming acidified lakes and rivers (adding lime to increase pH)

• recolonisation of damaged areas

• liming forestry plantations (to increase pH) --> trees increase pH as they remove nutrients

• international agreements

EVALUATION

• liming is effective, but must be repeated regularly and is expensive

• this treats the symptoms but not the cause

Clean Air Act

an agreement in North America in 1995 to attempt to lower sulphur dioxide levels back to pre-1980 levels - allowances for sulphur dioxide levels are set, but can be bought, sold and traded

precombustion techniques

the removal of sulphur from fuel before it is burned - this reduces the sulphur dioxide emissions