Unit 4 Pollution - Smoke, Smog and Photochemical Smog

What does smoke consist of?

Smoke is made up of the atmospheric particulates which are produced by the incomplete combustion of carbon-based materials

How do the size of smoke particles vary and how does this impact their properties and the harm they can cause?

The largest smoke particle is PM10, which is particulate matter less than 10 microns in diameter, there is then PM5, which is less than 5 microns in diameter and the smallest is PM1, which is less than 1 micron in diameter. Smaller particles remain in the atmosphere for longer (more persistent) and they are more likely to be inhaled.

What toxic chemicals can be found in smoke and what is another property of smoke?

Toxic chemicals in smoke can include fluorides, aluminium, leads, acids and organic compounds like phenol. Smoke can act synergistically with other atmospheric pollutants like sulphur dioxide.

What are the main sources of smoke?

• The combustion of coal, diesel and general combustible wastes, particularly in urban areas;

• In rural areas - combustion of crop waste, wood fuel, grasslands, forests - timber and burning charcoal to burn organic matter in the home - this is particularly used in Central Africa;

• Combustion of fossil fuels in industrial power plants, heating systems and vehicle engines

Why are smoke levels higher in some countries over others?

More populous countries tend to produce more smoke, such as India and China, as there is more vehicle traffic and these countries have large manufacturing industries with large numbers of factories and power plants

Industrialising counties - use cheaper fuels (fossil fuels), particularly coal, which is the cheapest and the most polluting fuel. Cleaner energies and management technologies likely not implemented as they are expensive.

What is the difference between smoke and smoke smogs?

Smog is a combination of smoke chemicals and fog while smoke is made up of particulate matter suspended in the air, caused by chemicals such as tropospheric ozone, particulate matter like pollen and dust, sulphur oxides, volatile organic compounds, nitrous oxides and ammonia gas.

What are the human health impacts associated with smoke and smogs?

• Respiratory diseases like bronchitis, asthma and lung cancer - particulates are mutagenic

• Chemicals on or in smoke particles can kill the cilia in the bronchioles, which makes it more difficult to clear inhaled particles and bacteria from the lungs, which can increase risk of infections. Some of the chemicals can be carcinogenic.

How does smoke and smog pollution affect other living organisms?

Smoke and smog reduces photosynthesis as smoke blocks light and substances in the smoke particles like heavy metals and acids may be toxic

How can smoke particles affect buildings?

Smoke particles can damage buildings because of the acids and organic solvents that they contain. Cleaning dirty buildings is also expensive.

How does smoke and smog impact the climate?

Large releases of smoke might reduce temperatures as the high albedo of smoke reflects the light so it doesn’t reach the ground where it may ordinarily have been absorbed and converted to heat. Large releases of smoke or smog might cause a ‘nuclear winter’ - thought that so much smoke would reach the stratosphere that the Earth would cool significantly for several years.

Why would a ‘nuclear winter’ be so concerning?

It would make survival on Earth much more difficult - crops would fail, livestock would die, and many natural ecosystems would be disrupted.

What is a final impact of smoke in the stratosphere?

It can deplete the ozone layer

Fog is a key component of smoke smogs. How does fog form? What makes the formation of fog more likely?

Fog normally forms when moist air is cooled until it reaches its dew point and then condenses as airborne water droplets. Temperature inversions make the formation of fog more likely.

What are some of the major impacts of smoke smogs in particular?

• Smoke that is part of smog is inhaled more easily

• Smog has a very high albedo and so the temperature inversion can last for long periods of time, which allows pollutant levels to rise to a high level

• Respiratory problems like bronchitis - particularly affects those with existing respiratory illnesses

What were the impacts of the London smog of 1952? How did the position of London exacerbate the impacts?

The position of London in a valley has caused problems with atmospheric pollution since the 1200s, and the impact worsened as the city grew. In December 1952, there was a 5 day period when anticyclonic weather conditions produced clear skies and low wind velocities so a temperature inversion formed and atmospheric pollutant levels rose. 12,000 people died as a result and they were mainly the elderly, or very young, or had existing respiratory health problems.

Smoke Pollution Control - Give an example of legislation which controls smoke pollution and describe how it works/what is regulated. Are there any limitations?

The UK Clean Air Act of 1956 restricted the use of fuels which produce smoke in large urban areas in the UK. It regulated domestic and industrial emissions for the first time. However - it took 30 years to deal with slow moving local authorities before smoke control programmes were finally completed and air pollution still causes 36,000 deaths in the UK each year. Legislation is often not regulated tightly enough and industrial polluters are often able to evade responsibility.

Smoke Pollution control - How might domestic sources of smoke be regulated?

Through increasing the use of fuels which don’t produce smoke, such as natural gas and electricity. This is something that cannot be enforced however, it relies on the choices of individuals.

Smoke Pollution Control - How are transport sources of smoke pollution regulated or controlled?

Diesel Particulate Filters (DPF) are fitted in the exhaust pipes of diesel engines. They trap up to 80% of smoke particles and are fitted to every car built after 2009. However, ash residue can build up in the DPF which can cause it to become blocked so it needs to be maintained properly.

Smoke Pollution Control from Industrial Sources - How do electrostatic precipitators work?

Effluent gases are passed through a chamber with many electrically charged wires or plates and the smoke particles within the gases are attracted to the charged wires and plates and they clump/collect together. As the particles acculmulate, they then fall to the floor as ‘fly ash.’ This is a method that is often used in coal-fired power stations.

What are the advantages and disadvantages of electrostatic precipitators?

Advantages - Handles large volumes of gas and heavy dust with low pressure drops; Has high collection efficiencies, including for small particles; Durable - long service life and requires little maintenance

Disadvantages - Takes up a lot of space; High capital (equipment) costs

Smoke Pollution Control of Industrial Emissions - How do cyclone separators work?

The effluent gases are forced to rotate in a cylindrical chamber, which throws the suspended particles to the outside of the chamber where they fall and collect. This cleans the gases which are then discharged via a pipe from the centre of the cylinder.

What are the advantages and disadvantages of cyclone separators?

Advantages - Low capital cost; ability to operate at high temperatures; can handle liquid mists or dry materials; low maintenance and space requirements

Disadvantages - High operating costs; Low efficiencies - limited particle size range

Smoke Pollution control for Industrial sources - What are scrubbers and how do they work?

Scrubbers use a fine water spray to wash out suspended solid particulate matter and dissolve soluble gaseous pollutants

What are the advantages of scrubbers?

Highly effective at capturing fine particles, removing up to 99% of particulates; can handle high temperature and humidity environments; can handle sticky material or abrasive dust

What are the disadvantages of scrubbers?

They consume significant amounts of water; require careful monitoring and maintenance to prevent the growth of bacteria and fungi; disposal of waste and pollutants must be managed carefully

Smoke pollution control for industrial sources - What does coal treatment involve?

Coal treatment involves heating coal which allows the tar that causes smoke production to be drained off, producing smokeless coal

Smoke pollution control for industrial sources - How do bag filters work?

Bag filters remove smoke particles from effluent gases by trapping them on a fabric filter

What are the advantages and disadvantages of bag filters?

Advantages - High filtration efficiency - trap up to 99% of particles and wide range of particles; simple maintenance; large capacity

Disadvantages - High initial cost; high operating costs - need to regularly replace filter bags; cannot handle high temperature gas

How can turbo chargers improve combustion efficiency in diesel engines?

Diesel engines produce the most smoke when the driver accelerates too quickly so too much fuel enters the engine for the amount of oxygen there is available to burn it. Turbo charges allow more oxygen to be delivered to the combustion chamber which increases the efficiency of the combustion.

What are photochemical smogs?

A haze which is caused by the reaction between nitrogen oxides and volatile organic compounds with solar ultraviolet radiation, which form tropospheric ground-level ozone as a brown haze above cities.

What emissions are involved in the formation of photochemical smogs?

Methane, Carbon Monoxide, VOCs and nitrous oxides (in the presence of UV/sunlight)

What are the main sources of these emissions?

• Vehicle engines - Nitrous oxides released in the exhaust gases - formed by the nitrogen and oxygen from the air which are drawn into the engine and then react with each other under high temperature and pressure conditions in the engines

• Industrial manufacturing plants - e.g. oil refineries - significant sources of NOx

• In the presence of sunlight and other pollutants like hydrocarbon vapours or tropospheric ozone, more toxic secondary pollutants can be produced such as PANs which constitute a large part of chemical smogs

• Unburnt hydrocarbons can come from a range of sources, particularly unburnt fuel in engine exhaust gases, fuel evaporating from fuel tanks, and spillages

What are the main impacts associated with photochemical smogs?

• Increased risk of respiratory infections like colds, flu and bronchitis and can make existing health problems such as asthma and heart disease worse

• PANs become more toxic at much lower concentrations than when NOx become toxic - they cause eye irritation, breathing difficulty, asthma, emphysema and an increased risk of heart attacks

• Tropospheric ozone is toxic in itself - causes asthma, bronchitis, and heart disease

Which cities are more prone to photochemical smogs and why?

LA, Mexico City, Paris and Beijing are among the cities that most experience photochemical smogs - this is because of their topography, heavy vehicle use and climate where traffic congestion is severe, temperatures are hot and temperature inversions are common

How do catalytic converters work to control the production of nitrous oxides?

They make use of a catalyst, which is usually platinum or palladium, to speed up the chemical reactions between oxygen and pollutants in the air to convert them into less toxic byproducts such as water vapour, carbon dioxide and nitrogen gas thereby oxidising pollutants into less harmful forms

How effective are catalytic converters?

They are extremely effective, turning 90% of harmful emissions into less harmful gases. They are one of the major reasons that there has been a 78% decrease in nitrous oxide emissions from 1970 to 2022.

How can unburnt hydrocarbons, another primary pollutant which can react to form photochemical smog, be controlled?

Using catalytic converters which oxidise the hydrocarbons to carbon dioxide and water

Vapours at filling stations can be collected, condensed and returned to the main fuel tank

Vapours can be collected and passed through an activated carbon filter where the hydrocarbons adsorb onto the carbon particles

Why might PM10 levels vary throughout the year?

Temperature inversions - PM10 may be trapped in cold dense air close to the ground; High UV levels - formation of photochemical smog; Increased demand for heating/energy/fossil fuels in the winter; Periods of high rainfall - wash particulates out of the atmosphere; Change in wind velocity/direction which affects dispersal; Increased pollen/dust in the summer - increased light leading to photosynthesis/blooms/flowering