Introduction: (Initial Observation)
The air is constantly moving. Convection currents and wind keep air circulating around the Earth. Polluted air is moved away and being replaced by fresh air. However in certain circumstances such as temperature inversions and faint wind, the air does not circulate and pollutants accumulate. Such accumulation of pollutants kills hundreds or thousands of people each year around the world.
On the week beginning 5th December 1952, four thousand Londoners died in the worst air-pollution disaster on record. Details…
Movements of the air also moves away pollutants. Wind is caused by atmospheric pressure differences resulting from differential heating of the Earth’s surface by the sun. Convection is the rise and fall of air depending on temperature. Cool air sinks because it is more dense, warm air rises because it is less dense. Air movement is an important factor in keeping the air free of pollutants. In this project we will study the possible relation between wind direction and temperature inversions. This project will help you to understand the consequences or results of temperature inversion. You will also see what causes some cities to be very polluted and others to have very little pollution?
Temperature Inversion is a condition in which the temperature of the atmosphere increases with altitude in contrast to the normal decrease with altitude. When temperature inversion occurs, cold air underlies warmer air at higher altitudes.
There are basically four types of temperature inversions:
- Marine Inversions
- High-Pressure Inversions
- Radiation Inversions
- Regional Subsidence Inversions.
Marine Inversions generally occur near cool oceans, such as in the western U.S. and western Europe. Marine inversions can turn a hot summer day at the beach into a cool, foggy, overcast shiver. The ocean is typically quite cool compared with the land, particularly at middle latitudes where the heating by sunlight is not strong. Air sitting over cold water also tends to be cool. Moreover, a great deal of water evaporates from the oceans. This moisture readily condenses in the marine mixed layer (or marine boundary layer) into stratus clouds and fog. Particularly on the western coastlines of continents, the marine air is blown inland by prevailing winds. In addition, the relatively intense heating of the coastal plain generates strong onshore sea breezes, which also draw marine air inland. Sea and land breezes are created by the contrasting temperature between the land and the oceans (or other large bodies of water, such as lakes). During the day, sunlight heats the land more than the adjacent ocean. Warm air rises over the land and is replaced by cool marine air flowing in near the surface. The warm air can circulate out toward the ocean above the marine boundary layer, setting up a temperature inversion in the coastal region. As a result, pollutants emitted into the marine air layer overland are trapped near the ground. In the evening, the land cools faster than the oceans. A reverse circulation may be set up, with cool air moving from the land over the water. Such a land breeze can last through the night.
A High-Pressure subsidence inversion can form when a stationary high-pressure system settles over a region. For example, during the summer season, the southern California coastal zone lies under the eastern edge of the Pacific high. This high-pressure system is a downward branch of the tropical Hadley circulation. Within the dome of high pressure, very dry air slowly subsides as it circulates clockwise about a center located off the coast of California. The air parcels brought to the Los Angeles basin thus arrive from the north and northeast. Subsidence compresses and warms the dry air as it descends into the lower troposphere. The dome of warm air then effectively traps the layer of cool marine air in the coastal region. A relatively shallow marine layer of several hundred meters to one kilometer in depth is formed. Separating the two air masses is a strong temperature inversion layer, which persists almost continuously during the spring and summer half of the year and appears occasionally at other times of the year. The temperature inversion suppresses convection and mixing, allowing pollutants to build up in the lower layer. Large weather systems that create conditions leading to high-pressure subsidence are fairly common. In some regions, these weather patterns regularly generate unusually intense hot winds. When the subsiding air encounters a cool stable layer near the surface, a strong temperature inversion can take place, as in the Los Angeles area.
A radiation inversion is created when heat is rapidly lost from the surface by thermal radiation. At night, the ground and the air just above the ground can cool off by radiating their heat energy while the air higher up remains warm. This is because air, particularly dry air, is a poor heat radiator, whereas land is an excellent radiator. The air just above land can lose heat by coming into direct contact with the surface. However, the air must be mixed downward to the surface. Recall that at night, convection dies away and the turbulent mixing of the lower atmosphere is shut off. The result is a very shallow layer of cold air that forms at the surface. Radiation inversions are most likely to form on clear nights with low winds. Clear skies are necessary for the surface radiation to escape; overlying clouds or fog absorb thermal radiation and effectively radiate it back to the surface. Calm winds also prevent the mixing of warm air at higher altitudes downward to the surface.
A regional subsidence inversion can be created when air flows over an obstacle such as a mountain range or blows from a high plateau and descends into a lower basin. Air that descends heats by adiabatic compression. This descending air therefore creates a hot wind, like the Santa Ana winds that often blow through Los Angeles. The air is typically very dry. It might be dry because of the source over land, or it might have happened as it rose over a mountain barrier, cooled, and lost water vapor by condensation and precipitation. As it is compressed, the dry air heats up. This produces the greatest warming for a given altitude change, which explains the unusually high temperatures of these winds.
If the descending air encounters colder air at the surface, it may be unable to push aside this denser air. The warm winds may then spread out above the surface layer, producing a temperature inversion. In other cases, strong subsidence winds fill a region with dry warm air that later cools at the surface by radiation, creating a radiation inversion. In southern California, weak Santa Ana winds often blow from the northeast across the mountain ranges to the north of the Los Angeles basin. These warm winds can trap colder denser marine air that is often present in the basin. These warm winds are usually associated with a high-pressure system.
Wind is the flow of air relative to the earth’s surface. A wind is named according to the point of the compass from which it blows, e.g., a wind blowing from the north is a north wind.
At night, the ground level temperature cools faster than the air above it. Pollutants become trapped under the layer of warm air.
As the sun rises in the morning, the ground level temperature warms up faster than the air above it, pushing the air upwards, which breaks up the warm air layer, allowing the pollutants to escape. However, if there is no wind, the air can become stagnant. This is illustrated below.
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
- How does wind direction cause temperature inversion?
- How does temperature inversion affect the circulation of the air by convection?
- Demonstrate the accumulation of pollutants caused by temperature inversion? (This is just a display or demonstration)
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
Independent variable (also known as manipulated variable) is the wind direction or the order in which cold and warm air are positioned.
You could also say: Independent variable (also known as manipulated variable) is the temperature of different layers of air.
Dependent variable (also known as responding variable) is the time it takes for different layers of air (fluid) to circulate and reach to a constant temperature.
Constants are the type of fluid, high and low temperatures.
Fluid = Liquid or gas
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
This is a sample hypothesis for question number 1:
The wind direction or the order in which hot and air cold are positioned has no effect on temperature inversion. In other words, regardless of the order of hot and cold air, they should mix until they get to a unified temperature.
This is another sample hypothesis for question number 1:
If the wind direction cause a warm layer be positioned above a cold layer, convection currents do not start and each layer will preserve its own temperature. This condition will continue for an extended period of time until another wind current change this order.
Additional sample questions and sample hypotheses:
1. Question: What is the relation between Wind Direction and Temperature Inversion?
Hypothesis: Wind direction can disrupt or even get rid of temperature inversion by moving the hot and cold air in different directions.
2. Question: What does temperature inversion cause?
Hypothesis: Temperature Inversion can cause major pollution.
3. Question: What causes some cities to be very polluted and others to have very little pollution.
Hypothesis: Population and the number of automobiles and factories are important factors affecting the pollution in a city. However, the location of the city and its surrounding topography can also be major factors on collecting and holding pollutants.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Demonstrate temperature conversion
Introduction: Temperature inversion in air can be demonstrated in small scale using water. All fluids (liquids and gases) follow the same rules when it comes to heat exchange and distribution. In other words convection currents are the main cause of heat distribution in all gases and liquids. In this experiment we will use water to demonstrate heat inversion. To make the results visible, we may use colored water. Water can be colored using tea, coffee or food dyes.
- Prepare a beaker half full with hot tea and another beaker half full with cold water. (Remind you that hot water is lighter than cold water; also, hot air is lighter than cold air)
2. Hold a spoon in the beaker of cold water at the surface of cold water. The tip of the spoon is touching the side of the beaker.
3. Gradually pour the hot tea over the spoon. (Spoon will void the force of falling liquid and allows the hot tea go over the cold water smoothly.)
4. Make observation and record what happened. How long does it take for the hot tea to mix with cold water below?
5. Repeat this experiment one more time; however, this time add cold water over the hot tea using the same method.
6. What happened? How long does the cold water remain over the hot tea.
(Note: For this experiment you could use cold tea and hot water. In other words the colored water could be the cold or the hot water. The choice of color has no effect on the outcome. Colors will only help us to determine if the warm and cold layers are circulating/ mixing or not.)
How does temperature inversion affect the circulation of the air by convection?
Introduction: Temperature inversion is a condition in which warm and cold layers do not circulate and maintain their temperatures. In this experiment we will simulate the temperature inversion as we did in the steps 1 to 3 of the previous experiment; however, this time we will measure and record the temperature changes over a period of time.
- Connect two glass thermometers using a piece of tape in a way that when you place them in the beaker, the bulb of one stays at the bottom while the bulb of other one stays in the middle of the upper half (near the top) of the cup. These two thermometers will be able to measure and show the temperature of different layers formed during your temperature inversion method.
- Prepare a beaker half full with hot tea and another beaker half full with cold water. Insert the thermometers in the beaker with cold water.
- Hold a spoon in the beaker of cold water at the surface of cold water. The tip of the spoon is touching the side of the beaker.
- Gradually pour the hot tea over the spoon until the bulb of the upper thermometer is fully submerged in hot tea.
- Observe and record both temperatures of cold water and hot tea.
- Repeat your observation and recording every 5 minutes for one hour.
- Repeat your experiment (steps one to 5) in an opposite direction. In other words, pour cold water over hot tea.
- How long does it take for hot tea and cold layers to get to the same temperature in both conditions (Hot over cold or cold over hot)
Your data table may look like this:
Temperature changes when hot layer is over cold layer.
|Time passed (minutes)||Temperature of cold layer||Temperature of warm layer|
|0 (Initial temperature)|
Experiment using saltwater:
As we have learned already, cold air is dense so it sinks, and warm is not very dense so it rises. Since warm air and cold air are constantly moving and cycling, this causes air to be circulated . However, the problem occurs when cold air is already at the bottom and warm air is already at the top. When this happens, there is no cause for circulation so air doesn’t move and it stays stagnant. This is what is called a temperature inversion. It causes major pollution and can be very harmful to cities.
The same goes for warm and cold water. Cold water sinks to the bottom while warm water rises. This experiment will demonstrate how a temperature inversion is formed and how pollutants get trapped close to the surface.
1. Fill the large glass bowl or aquarium a little less than half full with water. Put a few drops of red food coloring. The red food coloring represents warm air and as we already know, warm air is lighter than cold air.
2. Fill the measuring cup with water and saturate it with salt (keep adding salt until no more dissolves). Put several drops of blue food coloring in the salt water. The blue food coloring represents cold air and as we already know, cold air is more dense than warm air.
3. Pour the blue saturated water slowly and carefully through the funnel making sure that the other end of the tubing is on the bottom of the bowl. You should have two layers, blue on the bottom and red on the top. Why do you think this happened?. This is what generally happens in an inversion where you have cold heavy air under warmer, lighter air. This is a stable condition that inhibits vertical mixing and thus dilution of pollution.
4. Next, you will demonstrate what can happen to pollutants that are released under these conditions. Take green food coloring , which represents pollutants, and put it into the bowl drop by drop. It will layer out between the blue and the red. The pollutants do not mix, but become confined in the area they are emitted into.
5. Finally, you will show what happens when the wind begins to blow or a storm comes in and vertical mixing occurs. This can represent wind direction which can change temperature inversion. Mix up the contents of the bowl and the pollution will be diluted.
Materials and Equipment:
- 2 beakers
- 2 glass alcohol thermometers
- teat or food coloring
- Plastic spoon
- Large Glass Bowl
- Large glass measuring cup or pouring container
- Plastic or rubber tubing that fits the funnel
- Food Coloring: Blue, Red, and Green
- Salt Water
- Large Spoon.
Results of Experiment (Observation):
This experiment demonstrated how pollutants stay trapped in between cold and warm air in an inversion. The red food coloring (warm air) stayed at the top and the blue food coloring (cold air) stayed at the bottom of water. Then, the green food coloring (pollutants) layered in between the red and blue coloring. This demonstrates how pollutants stay stagnant in the air in an inversion, which causes many environment problems. Finally, when we mixed the solutions, the green food coloring where dissolved in the blue and red food coloring showing how pollutants get rid of when warm and cold air circulate.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did. This is a sample:
The pattern of temperature inversion and the circulation of air can be disrupted if it’s windy. The wind generates turbulence and produces mechanical mixing which carries some of the colder air aloft and brings some of the warmer air down to the surface. Thus, the cooling effect of the ground is felt over a deeper layer of the atmosphere, and no one level cools off as much.
Usually, there’s a sort of balance between two competing effects: the ground trying to cool off the lowest layer of the atmosphere, and the wind trying to mix the cooler air with some warmer air. Usually there’s still a temperature inversion; it’s just not as strong as it would be if there were no wind.
It’s difficult to forecast things like this, because temperature and wind are interrelated. If an inversion forms, that helps reduce the wind at the surface. Usually the winds at night are weaker than the winds during the day, for this reason, and the wind will frequently become calm at night at the surface as the lowest layer of air cools. The stronger the inversion, the weaker the turbulence, and the more difficult it is for winds to penetrate all the way down to the surface.
Nighttime conditions also tend to be dependent on the topography and vegetation near the observing station. If the station is in a valley, the cold air that forms at night can pool within the valley and form a strong inversion with very cold surface air. On the other hand, if the station is near the top of a hill, the cold air flows down the hill away from the station and the station can potentially remain warmer. Also, stations in the middle of a forest can more easily go calm near the ground than stations in the middle of grasslands.
Overall, Temperature Inversions can be affected by many things such as location, wind, temperature and other factors. One major cause of temperature inversion is when a city is surrounded by high elevations. In areas like this, air circulation is depended on convection currents to circulate the air and get rid of pollution. This is because there will be no winds since the high elevations block them off.
Several factors in the experiment could of thrown off the results. For example, the type of food coloring and how they are poured into the bowl can effect the overall results of the experiment. Also, when the water with the blue food coloring is poured into the funnel, they must be put all the way to the bottom of the bowl or aquarium or else they will mix with the other colorings and the experiment would also be thrown off. Those are possible errors that can affect this experiment. To be sure there are no errors, repeat the experiment several times and check your results to make sure they are all the same.
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