ESS TOPIC 6: Atmospheric systems and societies

Economic instruments to combat pollution

A variety of different economic tools can be used that include: Charging pollution emitters to encourage reduction in emission levels e.g. pollution tax, in which tax is charged according to the amount of pollution produced. Use of subsidies to encourage new technologies and support research into more efficient methods that reduce pollution from combustion of fossil fuels. Subsidies or tax credits to promote renewable sources of energy. Subsidising public transport. Use of road tolls and parking charges to discourage use of cars.

International and regional cooperation

Acid deposition is a transboundary issue, where the impacts may occur hundreds of miles downwind of the source of pollution. Acid deposition frequently occurs in neighbouring or nearby countries. Therefore, acid deposition can be considered as a regional rather than global problem. 1999 Gothenburg Protocol The Canada-United States air quality agreement in 1991

Cap and trade system for acid deposition

Cap-and-trade involves allocating the utilities with permits which allow them to produce a set amount of emissions (e.g. one tonne of emissions during the period of compliance). The utilities are then free to buy and sell emission permits to each other. Those that do not use their emission permits can gain economically by selling their surplus to others.

Measuring ozone levels

Ozone levels are measured in Dobson Units (DU) When ozone concentration falls, the ozone molecules become more dispersed within the same area which is sometimes referred to as "ozone thinning". Ozone levels are often measured using lasers, or a Dobson spectrophotometer, which measures the intensity of certain wavelengths. Measurements can be taken from the ground, from aircraft, balloon sondes (weather balloon) or using satellites. Normal levels range from 300 to 500 Dobson Units (that is the equivalent of 3mm to 5mm thickness of ozone). Due to levels of insolation ozone production is highest in the tropical stratosphere and is moved by prevailing atmospheric circulation systems towards the poles.

Formation of photochemical smog

Photochemical smog occurs when sunlight activates reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs) resulting in the formation of ozone and peroxyacyl nitrates (PAN). `VOCs are carbon based compounds with a low boiling point such as propane, butane and formaldehydes.

the primary pollutants that result in formation of acid rain include:

Stationary sources (i.e. fixed point sources) such as power station, industry and domestic boilers. Mobile sources which are predominately vehicles.

stratospheric ozone

Stratospheric ozone is found within the earth's atmosphere at around 25km in altitude. It is responsible for reducing harmful radiation reaching ground level.

Threats to stratospheric ozone

Stratospheric ozone is threatened by chemicals that react with the ozone and reduce its concentration. These chemicals are collectively referred to as ozone depleting substances (ODS) and often contain chlorine or bromine. Chlorofluorocarbons (CFCs) are one of the main groups of ODS.

Impacts of acid deposition on all ecosystems

The impact of acid deposition on aquatic and terrestrial ecosystems also depends on the capacity of the environment to neutralise the acidic input. The presence of alkaline calcium and magnesium compounds increases the buffering capacity of the soil and water, and reduces the effect of acid deposition. For example, calcium carbonate also referred to as limestone has a high buffering capacity.

Challenges of managing ODS's

Long life span of ODS ODS present in discarded equipment Lack of alternatives --> Illegal trade Lack of policing and enforcement

Main sources of NOx

emissions from industry, power stations and vehicles.

Natural emissions of ODS

emissions from volcanoes

Main sources of volatile organic compounds (VOCs)

industry, vehicles and solvents (e.g. used in paints and adhesives). Forest fires, whether accidental or intentional (e.g. slash and burn), also increase levels of VOCs and particulate matter (e.g. PM10).

Natural sources of sulphur dioxide + nitrogen oxides

sulphur dioxide: volcano emissions, hot springs and biodegradation of dead organic matter. nitrogen oxides: lightning and biodegradation of dead organic matter.

Impacts of acid deposition: Materials

Acid deposition increases the rate of stone erosion and metal corrosion. - weaken structures of buildings - damage infrastructure

Impacts of acid deposition: Aquatic ecosystems

Acid deposition can enter aquatic ecosystems either directly (e.g. precipitation as rain) or indirectly as run-off. It can lower the pH of the aquatic environment beyond the ability of some organisms to survive. oss of some species can cause a knock on effect through the food chain, adversely affecting other organisms (e.g. due to lack of prey). Some species may suffer from reproductive failure and many fish eggs do not hatch at pH below five. The decrease in soil pH also releases aluminium ions which are then leached into the aquatic system. Fish exposed to aluminium ions secrete excess mucus around the gills, preventing oxygen updates and leading to death by asphyxiation.

Impacts of acid deposition: Terrestrial ecosystems

Acid deposition on land can increase soil acidity. This lowering of soil pH can result in: Leaching of plant nutrients such as calcium, magnesium and potassium. This reduces the nutrients available for plant uptake. Mobilisation of aluminum ions that can damage plant root systems and can also be leached into nearby watercourses adversely affecting fish, as discussed above. Mobilisation of other toxic metals from the soil such as cadmium, lead and mercury which can then be leached into aquatic ecosystems adversely affecting aquatic organisms and potentially contaminating drinking water supplies. ------------------------------------------------------------------------ Exposure of plants to acid deposition also results in: Damage to the cuticle wax found on leaves which reduces plant photosynthesis. Lower tolerance to pests, disease and low temperatures. ------------------------------------------------------------------------ Overall these effects result in: Reduction in crop yield in agricultural areas. Loss of biodiversity and reduction in forest areas.

Other ODS

Additional ozone depleting substances (ODS) include: methyl bromide: used to eradicate pests, natural emissions from the ocean and the burning of biomass) halons: similar to CFCs but contain bromine instead of chlorine. They are used as fire suppressants in fire extinguishers.) hydrobromonfluorocarbons: HBFCs have similar properties to CFCs and contain either or both bromine and fluorine. Thet are used as solvents, cleaning agents and as suppressants in fire extinguishers. carbon tetrachloride: used as a solvent, dry cleaning agent, refrigerant and as a propellant for aerosol cans. methyl chloroform: used in industrial solvents, degreasing agent, correction fluid, spray adhesive and in aerosols.

Chlorofluorocarbons

CFCs are very stable compounds with long life times of between 65 and 110 years (depending on the specific compound). They were initially considered to be non-problematic to the environment due to their high stability. Coupled with the ability to produce them cheaply they soon became widely used as: Coolants in refrigerators and air conditioning systems Propellants in aerosol cans Cleaning agents for electrical parts Blowing agents in plastic foam. CFCs are not soluble and therefore cannot be removed by rain. Over a period of 10-20 years, the CFCs gradually migrate upwards from the troposphere (lower atmosphere 0-10 km above sea-level) into the stratosphere. Within the stratosphere, UV light breaks down the CFC molecule producing chlorine atoms that starts a chain reaction. The chlorine atoms react with ozone breaking it down and reforming chlorine atoms. This unsettles the previous ozone equilibrium. More ozone is destroyed than formed resulting in ozone depletion. Scientists have estimated that one molecule of CFC can destroy about 100,000 molecules of ozone. Eventually the chlorine atoms form hydrogen chloride which diffuses out of the stratosphere into the troposphere where it is washed out by rain.

Impacts of primary pollutants

Carbon dioxide and water vapour - increase in greenhouse gases resulting in higher temperatures Sulphur dioxide (coal and oil): *Sulphur dioxide is toxic and can act as: A potent respiratory irritant which causes inflammation of the lungs. It can trigger asthma attacks, chronic bronchitis and also increase the risk of lung infection. An eye irritant. A principal component of acid rain. Nitrogen oxides (Nox) - formed during combustion of fossil fuels - is a yellow brown gas that can reduce visibility and appears as a haze over urban areas. *Nitrogen oxides are: Respiratory irritants causing lung inflammation and triggering asthma. A principal component of acid rain. A precursor of photochemical smog and the formation of ozone. Particulates - combustion of fossil fuels PM10 = associated risk of cardiovascular disease PM2.5 = can travel deep into the lungs, increasing the risk of respiratory diseases and cancer. ---> premature death

Technological changes to help combat pollution

Catalytic converters: Catalytic converters could be used on all motor vehicles - reduce the amount of potential pollutants emitted by: Reducing NOx to form nitrogen gas and oxygen gas Oxidising carbon monoxide to form carbon dioxide. Oxidising VOCs to carbon dioxide and water. Increase energy efficiency - more efficient industrial processes, cars, and home appliances Alternative energy sources - solar panels, wind turbines, etc. Continuing research to: Improve energy efficiency of processes and products. Further improve the efficiency of renewable source of energy. Further develop low emission vehicles. Develop low emission fuels.

Industrial smog

Caused by smoke and sulphur dioxide emissions mixing with fog. Historically occurred in London in 1952 - industrial smog - 4 days Led to the The Clean Air Act of 1956.

In-situ clean up and restoration

Clean up methods have primarily focused around neutralising the acidic water by adding limestone (calcium carbonate) a process also referred to as liming. However, liming should be considered as only a temporary solution while the source of pollution is being reduced since cooperation between nations is necessary to reduce acid deposition at its source. Terrestrial systems can also be limed to increase the soil pH and immobilize toxic metals. On agricultural land, fertilizers may also be added to replace loss nutrients. In fuel oil - hydrodesulfurisation

Changing human behaviour to pollution

Educational campaigns Adopting practices at an individual level that reduce energy use, such as: Adopting use of more energy efficient devices such as refrigerators and washing machines. Turning appliances off when not in use, rather than standby mode. Making home modifications to reduce loss of heat to the outside through windows, doors, roof and flooring, such as efficient windows (e.g. triple layered windows), wall cavity insulation and ceiling and floor insulation. Decrease consumption of non-essential goods that utilise energy during production e.g. following the latest fashion can encourage over-consumption and waste. Reduce consumption of non-local goods that need to be transported long distances (i.e. with high road and air miles). Decrease individual car use, instead walk, cycle, use public transport or share vehicles (i.e. share transit or car pool). Adopt use of hybrid electric cars (which use both petrol and electricity) or electric car (only powered by electricity). This is particularly effective at reducing air pollution when renewable sources of energy are used to generate the electricity. Alternatively if fossil fuels are used to generate electricity, emission control technologies should be employed to reduce the levels of pollutants emitted.

Factors influencing production of photochemical smog

High emissions of pollutants from combustion of fossil fuels *often influenced by amount of industry, population size, mode of transport in the area(lack of public transport, etc.) High levels of sunlight, hence the highest levels of ozone occur during the sunniest part of the day. Calm or light winds which reduces dispersion and dilution and allows pollutants to accumulate at ground level. Dry weather conditions in which rain does not wash the pollutants out of the air. Where the topography allows pollutants to accumulated such as a valley surrounded by hills. The hills reduce the flow of air and allow the pollutants to concentrate within the valley. Tall buildings can also reduce air flow and allows pollution levels to increase. When a thermal inversion occurs (when cold air is trapped below a warm layer of air. Occurs during cold winter nights when the earth's surface cools and chills the layer of air next to it. Sunlight breaks the temperature inversion. - not long but inversions in deep valleys can take longer Common where the city is located in a valley, the weather is sunny, dry with little wind movement and where there are high emissions from cars or industry such as in Los Angeles, Rio de Janerio and Mexico City.

What is the greenhouse effect?

In the absence of GHGs, the heat would be radiated back into space potentially resulting in an average global temperature of about -18°C and a very different environment to the one we currently live in. In the presence of GHGs, the long wave radiation is absorbed by the gases resulting in warming of the atmosphere to an average global temperature of around 15°C. This is commonly referred to as the "natural greenhouse effect". Therefore, human activities that alter the concentration of GHGs in the atmosphere can impact on global temperatures. Not all energy from the sun entering the earth's atmosphere reaches the ground. Some of the solar energy is reflected back into space by clouds, particles in the area and surfaces such as ice and snow. This reflection is known as the albedo effect.

Legislation to combat pollution

International agreements that set goals and are adopted into national polices (1999 Gothenburg Protocol) Legislation can be used to set more stringent emission standards for industry, power generation and vehicles. This can encourage use of low sulphur fuel, such as gas or adoption of renewable energy sources such as solar or wind in order to meet the more stringent standards. Planning regulations: Incorporation of cycle paths. Road lanes restricted to public transport or those adopting vehicle-sharing (such as shared transit or car-pooling). Adoption of vehicle free zones and park and ride schemes.

Changes in stratospheric ozone levels

It has been found that during the dark, cold days of winter, the wind creates a swirling mass of air called a "polar vortex". This prevents air from the lower latitudes entering. Cold winter temperatures lead to the formation of polar stratospheric clouds (PSC) within the polar vortex. CFCs and ODS molecules react in the PSC and form chlorine atoms and other ozone depleting chemicals. In the absence of sunlight, they are unable to react with ozone and hence accumulate within the PSC. When the days become lighter, sunlight energy releases the chlorine and other chemicals that cause ozone destruction, rapidly reducing levels of ozone which reflects the seasonal changes observed. Sunlight gradually breaks up the polar vortex which allows movement of air containing ozone into the area.

composition of the earth's atmosphere

Nitrogen and Oxygen

Impact of tropospheric ozone

Ozone formed at ground level: Is a highly reactive gas . Causes inflammation of the lungs causing coughing, wheezing and contributing to asthma. Reduces lung function, contributing to lung disease and premature death. Irritates the eyes and nose. Damages fabrics such as rubber and plastics. Damages cells in the leaves disrupting photosynthesis and reducing plant growth which affects crops and forest. In crops such as wheat, soya beans, tomatoes and cotton, smog has also been found to increase risk of infection. The impacts of ozone on health, reduced crop production and material degradation also contribute to a significant economic loss.

Policies to reduce air pollution

Pollution reduction policies can employ the following approaches: Altering human activity that produces air pollution. This can be achieved by changing human behaviour and may: Involve education and campaigns to inform the public of the effects of air pollution and ways in which they can reduce emissions. Be supported by economic instruments. Involve the use of alternative technologies. Legislation to prevent or regulate the release of air pollutants. Clean up and restoration of damaged systems.

Progress of banning ODS's

Production of chlorofluorocarbons CFCs and related chlorinated hydrocarbons have stopped and are resulting in atmospheric levels stabilising or declining. Production of halons has stopped, but atmospheric levels continue to rise, possibly due to emissions from old fire extinguishers. HCFCs, replacements for CFCs, are still produced and therefore atmospheric levels continue to rise. Production of HCFC is to cease by 2030. Some countries banned the use of methyl bromide prior to the 2015 deadline, contributing to the decline in atmospheric levels recorded. Although, some nations are struggling to find a suitable and cheap alternative and under special exemptions continue currently to use methyl bromide as a fungicide.

UV-B radiation and human impacts

Sunburn and premature aging of the skin (i.e. wrinkled and leathery) which may increase risk of skin cancers. Skin cancers e.g.: Non-melanomas such as basal or squamous cancers (both can usually be treated if found early). Malignant melanomas that can spread rapidly and be fatal. Cataracts, in which clouding of the lens reduces vision. If untreated it can lead to blindness. Immune-suppression in which the ability of the immune system to function is impaired and this can increase risk of infections. Health problems in animals e.g. cancers and damage to their eyes. Reduction in crop production e.g. studies have demonstrated impaired growth and subsequent lower yields from crops such as rice, soya beans and sorghum. Reduced phytoplankton growth which could have impacts throughout the aquatic food web. Human food supply could also be affected through the reduction in available seafood. In addition with less primary production, the uptake of carbon dioxide falls impacting on climate change. Reduction in forest productivity which will reduce the amount of carbon dioxide absorbed from the atmosphere further exacerbating climate change.

Management of stratospheric ozone: International agreements

The Vienna Convention for protection of ozone layer (1985), was influential in producing the Montreal Protocol 1987 which sets specific targets on reduction of ODS. The UN also set up the UNEP OzonAction Programme to assist developing countries to achieve compliance through technical advice and multilateral funds. Developed countries contribute to the funds to help developing countries to switch from using ODS. It is left to each nation to best decide how they will comply with the targets set in the Montreal Protocol. The standard approach is to incorporate it into national legislation which feeds into policy and action across the country.

Formation of ozone

The amount of ultra violet (UV) radiation that reaches the stratosphere is sufficient to drive the formation of ozone. Ozone is formed by sunlight energy breaking the bonds within diatomic oxygen molecules to form atomic oxygen which in turn reacts with oxygen molecules to form ozone. At the same time, ozone molecules react with oxygen atoms to reform oxygen molecules. Without the influence of pollutants, the rate of ozone formation is usually the same as the rate of ozone destruction, leading to a constant level of ozone.

Acid deposition

The pH of natural deposition is usually between pH 5 and 6. Emissions from human activity can further lower the pH of any deposition. This acid deposition occurs as a result of primary pollutants of sulphur dioxide and nitrogen oxides reacting in the atmosphere to form secondary pollutants of sulphuric acid and nitric acid respectively. This results in the pH declining to below five. The main human based source of the primary pollutants, sulphur dioxide and nitrogen oxides is the combustion of fossil fuels.

Troposphere

This is the layer closest to the earth's surface and includes where we live. It extends up to about 10km above sea level and is where: The earth surface absorbs heat from the sun. The warm earth then heats the atmosphere through conduction. The troposphere is warmest near the earth surface with temperature declining by around 6.5°C per kilometre. Wind speeds increase with height. The jet stream which blows powerful winds towards the east occurs at the top of the troposphere. Most of the atmospheric mass is found. This includes nearly all the water vapour, clouds and pollutants. Most of our weather occurs. Humans and other organisms have most interaction e.g. through exchange of gases or through introduction of pollutants. The greenhouse effect occurs and helps to regulate the temperature of the earth.

Thermosphere

This layer extends beyond about 80km to between 500km and 1,000km. Within the thermosphere: UV and X-radiation from the sun is absorbed which breaks apart molecules into atoms (oxygen, nitrogen and helium atoms are the main components in the upper thermosphere). The temperature increases with height and can reach beyond 2,000°C. This heat can cause the layer to expand causing variation in depth overtime from 500 to 1,000km.

Stratosphere

This layer extends from 10 to 50km above sea level and is where: Stratospheric ozone absorbs ultra violet radiation from the sun. Temperature is constant at about -60°C in the lower part of the stratosphere, which is shielded by the ozone layer but then increases with altitude. The air is dry. Winds increase with height. The stratopause marks the end of the stratosphere and is where the temperature remains constants with altitude.

Mesosphere

This layer ranges from about 50 to 80km and is where: Without the presence of ozone or other particulates to absorb UV radiation, the temperature declines with height. It is the coldest part of the atmosphere with temperatures falling to -100°C. There are strong winds with speeds up to around 3,000km/h. The mesopause occurs at the end of the mesosphere and is where the temperature does not change.

Effects of stratospheric ozone

UV-A (longest wavelength between 315-400nm) - ozone is unable to absorb this radiation and it passes through to the ground level. UV-B (wavelength between 280-315nm) - ozone absorbs most of this radiation but some passes down into the troposphere layer below. UV-C (shortest wavelength with highest energy 100-280nm) - ozone and atmosphere is able to absorb all the UV-C radiation, preventing it from reaching the earth's surface.

Clean-up measures and restoration

Use of "scrubbers" can be used by industry and power stations to filter emissions prior to discharge to remove primary pollutants such as particulate matter and sulphur dioxide. reforestation and replanting of areas affected by the smog.

Main GHGs and their sources

Water vapour is the most abundant GHG. A rise in temperature results in more water vapour leading to further warming, which allows more water to evaporate and this positive feedback cycle continues. Carbon dioxide concentrations are increased by burning of fossil fuels, respiration, volcanic activity and deforestation. Plants and trees act as carbon sinks removing carbon dioxide from the atmosphere and effectively storing it in the form of biomass, hence deforestation also reduces available carbon sinks, thereby further exacerbating the situation. Methane arises from emissions from livestock, anaerobic decomposition of waste, rice cultivation and fossil fuels. Nitrous oxide sources include fertilizers, combustion and industrial processes. Chlorofluorocarbons (CFCs) and hydrochloroflurocarbons (HCFC) have been used as liquid coolants (in refrigerators and air conditioning systems), in the production of plastic foam and as industrial solvents. Perfluorocarbon is used in production of aluminium. Sulphur hexa-fluoride is used in production of magnesium.

Deposition can occur as:

Wet deposition e.g. when pollutants are incorporated into the clouds or falling raindrops and result in acidified rain or snow. (rain, snow, sleet) Dry deposition, when atmospheric pollutants are removed by gravity or direct contact under dry conditions e.g. when emissions of ash or dry particles from power stations are absorbed directly onto plants and buildings. (particulates and gasses)

Dispersion and distribution of acid deposition

When sulphur dioxide and nitrogen oxides are emitted into the air, they can be transported long distances by prevailing winds. Tall smoke stacks have often been used to reduce local pollution by increasing dispersion of the pollutants. The topography downwind of the source of pollution can also effect the distribution of acidic deposition. In mountainous areas, moist air masses are forced to rise, which causes cooling and condensation resulting in precipitation potentially increasing acidification in the area.