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Transcript of Photochemical Smog
This reactions occurs due to the extremely high temperature inside the chambers (around 2000 degrees Celsius), and the nitrogen and oxygen atoms react.
photo credit Nasa / Goddard Space Flight Center / Reto Stöckli
What is Photochemical Smog?
The brown haze of air pollution that is found in many large cities and suburbs is known as photochemical smog. This environmental issue wreaks havoc on our home planet - causing devastating damage to our world and irreversible effects on human health. In this presentation, we will be exploring the history and chemistry of photochemical smog. We will be looking at its effects on the environment, and the actions we are currently taking to prevent this dangerous issue. But firstly, let us tackle the boring stuff (aka history) behind this environmental issue before moving onto the fun chemistry of it.
(Brief) History of Photochemical Smog
Formation of Chemicals in Photochemical Smog
Both Nitrogen Monoxide and Nitrogen Dioxide are primary pollutants that make up photochemical smog from the combustion of oil, coal or gas in automobiles and industry. These are not produced by the combustion of fuel itself, rather Nitrogen Oxides are side products that occur in the main reaction.
Ozone (O3) is a secondary pollutant present in Photochemical Smog. This compound is formed from the reaction of an oxygen radical and O2 gas to produce O3.
Carbon Monoxide is a toxic chemical that is produced from the combustion of oxygen and fuel in automobiles. This compound (CO) is produced when their is limited oxygen gas in the reaction, causing Carbon Monoxide gas to be produced as a product.
Formation of Chemicals in Photochemical Smog
Volatile Organic Compounds are chemical compounds that are organic due to the presence of carbon within them. Due to high vapor pressure (easy to vaporise at normal atmospheric pressure), VOCs are gases at room temperature. As VOCs describe any chemical that has high vapor pressure and is organic, there are over 600 types of VOCs within photochemical smog. Examples of VOCs include: benzene (C6H6), dichloromethane (CH2Cl2) and formaldehyde (CH2O).
Effects on the Environment and Human Health
How humanity is reducing Photochemical Smog and it's current development and problems
Although there are no actions that are being done to actively rid photochemical smog, there are certainly many campaigns and activities that can be done to reduce the amount of photochemical smog present on Earth. As we are the ones that cause this environmental issue, it is up to us to reduce the amount of photochemical smog produced through simple actions that will rarely affect our current lifestyle.
- The term photochemical smog was first coined in the 1950s to describe the brown haze in major cities or areas with high levels of industry.
- Photochemical smog was the term used to describe chemical components released and formed from automobiles and industrial machinery that reacted with sunlight.
Nitrogen Monoxide (2)
Another way Nitrogen Monoxide is formed is in the reaction of Nitrogen Dioxide and Sunlight.
This reaction produces two products: Nitrogen Monoxide (NO) and an Oxygen radical (O)
-Photochemical Smog first became an environmental issue during the Industrial Revolution. With the creation of large industries and factories, and society's reliance on coal, photochemical smog became a major environmental and health hazard as air pollutants were being released by the ton from industries.
- Technological inventions and advancements, such as the creation of automobiles, also contributed to the rising issue of photochemical smog. As society began to become dependent on automobiles and industrialization , Photochemical Smog became more prominent as an environmental problem - on par with other environmental issues such as Acid Rain and Global Warming
How this issue was created
- Photochemical smog is split into two major categories: Primary and Secondary Pollutants
- Primary Pollutants include Nitrogen Oxides and Volatile Organic Compounds (VOCs). These are called primary pollutants as these chemicals are introduced into the atmosphere by vehicles and industries.
-Secondary Pollutants are the chemical products from the reactions of Primary pollutants. Depending on the type of reaction and chemicals, there are many different secondary pollutants within photochemical smog. Major chemicals include Ozone, PAN (Peroxyacetyl Nitrate) and aldehydes ( R-CHO)
- For Photochemical Smog to be created, certain conditions in the environment must be met:
1. There must be a high presence of VOCs and Nitrogen Oxides in the atmosphere. These types of conditions are usually found in major cities (due to high levels of vehicles) and industry areas (factories and infrastructures release large amounts of these chemicals).
2.The climate must be warm, sunny and dry in order for the high presence of VOCs and Nitrogen Oxides to react. The time of day that most "brown hazes" occur is during late morning to the afternoons. This is due to the high level of lingering air pollutants after morning work traffic reacting with the intense light of late morning/early afternoon.
3. The temperature of low-level atmosphere must be lower than the temperature of high-level atmosphere. As hot air rises and cooler air falls, for photochemical smog to remain near the earth's surface - the temperature of the atmosphere above it must be higher. If the temperature of the photochemical smog was higher, it would rise up and be released or diluted.
Primary and Secondary Pollutants
Conditions for Photochemical Smog to Occur
Nitrogen Dioxide is formed when the Nitrogen Monoxide gas released from the combustion chamber cools and reacts with the oxygen gas present in the atmosphere.
Nitrogen dioxide is the reason why photochemical smog is brown.
Ozone is formed from the free oxygen radical in the previous reaction reacting with oxygen gas in the atmosphere.
Nitrogen Dioxide (2)
Another reaction that occurs in photochemical smog that results in Nitrogen Dioxide is the reaction of Ozone and Nitrogen Monoxide.
As you can see, an obvious cycle occurs as the Nitrogen Dioxide produced will react again with sunlight to produce Nitrogen Monoxide and an oxygen radical. This cycle continuous until there is not enough sunlight provided for Nitrogen Dioxide to react.
Volatile Organic Compounds (VOCs)
Ozone and Peroxyacetyl Nitrate (Environmental Effects)
Nitrogen Oxides upset the balance of chemical nutrients in water areas - leading to the deterioration of water quality. Aquatic plants and animals will be negatively affected by the increase of nitrogen due to the acceleration of eutrophication (see diagram). Due to eutrophication, there is a depletion of oxygen in the water and as a result, many aquatic animals and plants die.
Nitrogen Oxides can react with other substances in the air to form acidic substances - leading to the cause of Acid Rain. Nitric Oxides can also react with common organic chemicals to produce toxic products that may cause biological mutations to plants and animals. Some of these toxic products include:
Nitrosamine and nitrate radical.
Small levels of nitrogen oxides intake can lead to nausea, irritation in eyes and shortness of breath, whilst large levels of nitrogen oxide intake can lead to burning spasms, major respiratory problems, swelling of the throat and even premature death.
Nitric Oxides can react with ammonia and other organic chemicals to produce nitric acid and other similar acids. These particles can damage lung tissue and cause minor and major respiratory problems.
VOCs can cause acute and chronic health effects.
Acute health effects include: Nausea, dizziness, eye irritation and shortness of breath.
Chronic health effects include:
cancers (lung, liver, kidney), respiratory diseases , asthma and even premature death
Some VOCs are extremely efficient greenhouse gas (such as methane), which contribute to global warming.
VOCs can react with Nitrogen Oxides to produce Ozone and Peroxycetyl Nitrate.
High levels of ozone in low-level atmosphere affects the photosynthesis of plants and hinders the overall growth of them. Many plants suffocate or are stunted by high-levels of ozone present in low-level atmosphere.
Peroxyacetyl Nitrate affects the environment similar to Ozone. PAN reduces the ability of plants to reproduce, store food and grow. It reduces photosynthesis and discolours and kills the leaves of the plants.
Low-level atmosphere ozone also causes respiratory problems to both animals and humans. Ozone can irritate or even damage the lungs, causing respiratory illnesses in both the lungs and the heart. Ozone can also cause irritation in the eyes and impair vision.
Ozone and Peroxyacetyl Nitrate (Health Effects)
Peroxyacetyl Nitrate show similar health problems as Ozone. However, due to its ability to dissolve in water and react more readily, PAN is a more toxic and dangerous compound than Ozone.
Some health effects that PAN causes are: emphysema, impaired breathing, acute pulmonary edema and lung lesions. People with heart and lung disease, children and the elderly are the most susceptible to PAN.
As there are many different chemicals inside photochemical smog, there are a variety of health and environmental problems that arise due to this issue. We will briefly touch the main pollutants present in photochemical smog and outline the environmental and health effects of these chemical compounds.
Reduce amount of automobiles on the road
To minimise photochemical smog, we should reduce the amount of times we travel by car and instead think of alternative methods to get to our destination. Bicycles, walking and public transportation are just some of the actions we can take to minimize the amount of photochemical smog in our atmosphere. However, as modern society live apathetic and lazy lifestyle, we require faster and more luxurious means of travel - hence our dependent on singular automobiles (such as cars).
Car manufacturers are creating new cars that emit less pollutants per km travelled, or rely on a new method of powering their vehicles. With the commercial outbreak of Toyota's first electric car, the Prius, other car companies have been following suit creating electrically powered cars to minimize the amount of pollutants emitted as a waste. However, one problem that arises is the slow speed and duration of electric power. For the moment, many car manufacturers are using catalytic converters to reduce vehicle emission. The tailpipe is coated with a precious metal (such as platinum) that converts:
-NO to N2
-CO to CO2
-Hydrocarbons to H2O and CO2
As a society, we should begin to embrace greener ways of producing energy and ignore the money costs for the greater good. Installing Solar Panels, using machines that have high energy efficiency ratings and reducing the amount of electricity running in the house are some ways that we can reduce the amount of air pollutants being released. Industries and factories should begin to consider alternate ways to produce materials/energy such as using wind/solar/nuclear power.
Smog watch is a voluntary pollution prevention program that is aiming towards reducing the amount of air pollutants released into our atmosphere and making sure that we don't exceed the federal health standard for ozone. Many volunteers ask news reporters, TV presenters and weathermen to advocate the reduction of air emission.
"Perfect" Conditions for Photochemical Smog
Volvo concept electric car
Key to Chemical Equations
When a VOC is released into the atmosphere, it reacts with a hydroxyl radical (formed from NO2 reacting with sunlight) to form water and a hydrocarbon radical.
This hydrocarbon radical reacts extremely quickly with oxygen gas in the atmosphere to produce a RO2 radical.
Dr Richard Foust. 2008. Photochemical Smog. [ONLINE] Available at: http://mtweb.mtsu.edu/nchong/Smog-Atm1.htm. [Accessed 02 July 13].
The RO2 radical reacts with the primary pollutant Nitrogen Oxide to produce Nitrogen Dioxide and a RO radical.
Again, as soon as the RO radical has been produced, it interacts quickly with the oxygen gas in the atmosphere to produce an Aldehyde and a hydroperoxyl radical.
The aldehyde reacts with a hydroxyl radical to produce an acyl radical and water.
This acyl radical reacts quickly with oxygen gas to produce an acyl peroxy radical.
Finally, this Acylperoxy Radical reacts with Nitrogen Dioxide to produce an acylperoxy nitrate. As "R" represents any hydrocarbon, there are many types of acylperoxy nitrates in photochemical smog - one of the more prominent of these molecules being PAN (Peroxyacyl nitrates - CH3COOONO2)
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And of course:
Lukins, N, 2006. Heinemann Chemistry 1. 4th ed. Australia: Pearson Heinemann.
Thanks For Reading This Presentation!!
Hopefully this presentation has encouraged you to take action against the dangers of photochemical smog and become aware of the consequences of humanity's actions in creating toxic chemical compounds present in this environmental issue.