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A study of air purification methods

A study of air purification methods

Introduction: (Initial Observation)

With the increase of air pollution and it’s harmful health effects we need to come up with methods to filter the air or otherwise produce fresh air for indoor use.

Currently fossil base fuels are the main cause of air pollution in cities, roads and industrial areas.

In this project you will gather information and perform an experiments on an existing or new method of air purification.


If you have any questions, click on the help button at the top of this page to send me your questions. I may respond by email, but often I update this page with the information that you need.

Project Advisor

The method and experiment that I have proposed will use water to filter air.

Information Gathering:

Find out about air pollution, filtration and purification. Read books, magazines or ask professionals who might know in order to learn about different types of pollutants in the air and known methods for removing each pollutant. Keep track of where you got your information from. Following are samples of information that you may gather.

There are a large varieties of pollutants in the air and there are many different air filters that can partially filter such pollutants.



Most common air filters are made of cellulose or plastic fiber; however, some air filters are made of plastic foam. Foam and fiber filters are only able to collect dust particles that are floating on the air and their size is larger than filter passages. These filters are not able to absorb gases and hazardous fumes.

Air filters are used in most air conditioning systems and some machines.

A large portion of air pollution in urban areas is caused by cars and heating systems burning fossil based fuels. Large concentration of smoke and carbon dioxide is a cause of dizziness and respiratory disease.

Air pollution is not limited to the pollution caused by fossil base fuels. Bacteria, fungi (such as mold), pollen, some gases, some vapors and many other particles are among the pollutants of the air. When a group of people stay in a closed environment such as an airplane with no or little air exchange, bacteria in the air accumulate and the risk of transmission of disease increases. Gases from incomplete burning of fuels can be fatal. Fumes from chemicals, solvents and detergents can be poisonous. Mold, pollen and many other microorganisms can cause disease or allergic reactions.

Particle pollution is presence of excess amount of dust of different nature on the air. Dust particles include lint, fiber, dead skin cell, cells of dead animals and insects, pollen and dust from trees and soil.

Using UV in air filtration:

Depending on the type of pollution, different methods of purification or filtration must be used. For example if we are doing purification with the purpose of removing airborne bacteria, we just need to make sure that bacteria in the air become inactive. We do not need to physically remove the bacteria. For example air may just go trough an air duct where it is exposed to a germicidal radiation for sufficient amount of time. One common form of germicidal radiation is ultra violet radiation.

Ultraviolet light has been used for years by the medical field to sanitize rooms and equipment, and it is recommended for its ability to destroy germs and other biological pollutants.

Ultraviolet light from the sun destroys viruses, bacteria, fungi, and other pollutants, including mold spores. Some UV lamps offer a much higher concentration of ultraviolet light than even the sun. UV light damages the DNA structure of the microorganism, causing its destruction. Once the UV light sterilizes the pollutant, it is no longer able to reproduce (which is how harmful microorganism levels are sustained and increased). It then becomes inactivated, or microbiologically dead, rendering it harmless.

How to filter gases?

Harmful and poisonous gases require a different method of filtration. Activated carbon is a very porous substance that can adsorb large amount of gases. It is mainly used in gas masks.

Fumes of chemicals such as acids and solvents can often be removed from air by condensation or by washing the air with water. The same method can also be used for some particles.

Activated carbon is carbon that has been treated with oxygen to open up millions of tiny pores between the carbon atoms. There are so many of these that one pound of activated carbon has a surface area of 60 to 150 acres.

Activated carbon is the substance that keeps military personnel safe from poisonous gasses. It is used to adsorb odorous or colored substances from gases or liquids. The word adsorb is important here.

Adsorption is the process where certain chemicals are attracted to activated carbon and then bond to it. The millions of pores in the activated carbon provide enormous surface area to trap these chemicals.

An activated carbon filter acts like a sponge. When it is full it can adsorb no more. The more carbon you have the more you can adsorb

Many gases and fumes can be washed by water. Water can also collect particles from the air. Water curtain is a popular system used in paint booths and other dust producing manufacturing processes.

For more information search the Internet for:

  • Water curtain
  • Electrostatic air filter
  • Activated carbon filter
  • UV air purifiers
  • Dust filters or Air filters

Gas washer is an apparatus within which gas from the condenser is brought in contact with a falling stream of water, to precipitate the tar remaining in it.

Different types of the above filters are available for use and test. You may also decide to make a model of any of the above filters.

I am wondering if small bubbles of air can enter water and purify while coming up to the surface of water.

I have seen water bubbles in aquariums and I think that water does actually remove dust particles and certain fumes from the air. I also think that we can add chemicals to water to increase its effectiveness in absorbing gases and fumes. Additives such as detergents can possibly assist collecting hydrophobic fumes. Acidic additives can help collecting alkaline fumes such as ammonia. Also alkaline additives such as caustic soda can help collecting acidic fumes such as the fumes of hydrochloric acid, acetic acid and nitric acid.

In this project you will use water to filter or purify air. We call it air washer for the purpose of this project.

Question/ Purpose:

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.

The purpose of this project is to design and test an air filtration device that uses water to remove the impurities from the air. Also determine how does the depth of air nozzles affect the filtration rate .

Identify Variables:

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.

There are many variables that affect the filtration process and can be studied in this research. Among these variables are:

  • The size of bubbles
  • The distance the bubbles travel to the surface of water
  • The pH of water
  • The type of pollutant
  • Addition of certain additives

You can select any of these variables as the independent variable or manipulated variable and test to see how it may affect the filtration rate of air with certain impurities. You may also come up with certain questions that can be the subject of your project. For example you may ask how does the size of bubbles affect the filtration rate in an air washer filter. Or you may ask how does the depth of air nozzles affect the filtration rate in an air washer filter.

  • Independent variable is the depth of air nozzles.
  • Dependent variable is the filtration rate.
  • Controlled variables are the size of air nozzles, the type of pollutants, type of water, additives and water pH.


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.

Water is able to absorb particle pollutants as well as certain fumes and gases. More depth of nozzles increases the distance bubbles travel to the surface and increases the rate of filtration.

Experiment Design:

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.”

The image on the right shows an air filter. Most air filters like this absorb dust and solid particles. They do not filter bacteria, viruses, gases and chemical fumes. In the following experiment you design and make a filter that can also absorb certain gases and fumes as well as particles.

Experiment 1:

In this experiment we pass the air trough water, so water can absorb particles and gases in the air.


  1. Get a narrow mouth glass bottle and fill it up to 3/4th with clean water.
  2. Insert two pipes in the bottle. One pipe is long and goes all the way down to about an inch to the bottom of the bottle. The other pipe is short and ends around the neck of the bottle.
  3. Seal the neck of the bottle with chewed gum or hot melt glue.
  4. Blow in the long pipe or suck the short pipe. You should see air bubbles coming out of the bottom of long pipe and rising to the surface.

5. Your air washer is now ready for test. Place some non hazardous contaminants in the opening of air input pipe and suck the air from the air output pipe. Do you feel presence of any contaminants? Contaminants that you can test are vinegar, salt, flour.


Cleanup cigarette smoke:

A special design of air washer, known as water pipe, nargileh or ghalian is used for smoking tobacco in middle east. Water absorbs part of hazardous material formed by burning tobacco and reduces its smoke and other harmful chemicals.

If you know someone who smokes, you may ask him to use your water pipe to smoke a cigarette. Cigarette must be placed on the opening of the air input pipe and the smoker will suck the gases from the air output pipe.

Part of smoke and harmful chemicals of cigarette will be dissolved in water. This may reduce the clarity of water and change its color.

In this experiment, the impurities of air are being absorbed by water. Later you may test this water to determine the presence of harmful material in it. For example you may experiment to see how long can a goldfish survive in such polluted water.

Note: If you have access to a laboratory air pump, you can connect the air output pipe to the input of the air pump. In this way no one has to suck the air.

Cleanup vinegar odor:

In a chemical or food manufacturing facility, excess amount of vinegar (acetic acid) fumes can be irritating and harmful. Can a water filter absorb acetic acid fumes?


  1. Connect a plastic hose to the air input pipe and insert it in a bottle of vinegar and secure it right above the surface of vinegar.
  2. Use a pump or your mouth to suck the air from the air output pipe.
  3. If the fumes of acetic acid are being dissolved in water, the pH of water will decrease and water will get acidic. You can determine the pH of the water using a pH indicator paper or a pH meter.

Cleanup ammonia fumes:

Ammonia is another chemical with irritating fumes. Ammonia solution is used as a detergent and is available in many supermarkets. If you have access to a pump, you can perform the above experiment with ammonia instead of vinegar. Ammonia fumes increase the pH of the water and make it alkali.

How effective is your filter? test it in experiment 2

Experiment 2:

In this experiment you determine the effect of nozzle depth in the rate of filtration. Use the air washer device that you made in experiment number 1 and a pump for this experiment.


  1. Connect a plastic hose to the air input pipe and insert it in a bottle of vinegar and secure it right above the surface of vinegar.
  2. Use an electric pump to suck the air from the air output pipe of air washer for 10 minutes. If you are using a hand pump, count 100 pumps instead of 10 minutes.
  3. Measure and record the pH of the water after you stop pumping.
  4. Use titration method to determine the amount of vinegar absorbed by water.
  5. Repeat this experiment for different depths of nozzles in water and record the results in a table like this:
    Nozzle Depth pH after test Acid concentration after test

You can also use the above table to draw a line graph.

Additional Notes:

Scientific method requires having a control. A similar experiment with no pumping can be the control. By having a control, you have a proof that changing the pH of water and presence of acetic acid in water is the result of filtration and not an unexpected event such as fermentation.

How do you titrate acetic acid?

The reaction formula of acetic acid and caustic soda is:


One molecule of acetic acid neutralizes one molecule of sodium hydroxide.

Molecular weight of acetic acid is 60. Molecular weight of sodium hydroxide is 40. So 60 grams of acetic acid can neutralize 40 grams of sodium hydroxide.

For titration, you can use a 0.1 normal solution of sodium hydroxide. You can buy a normal solution and dilute it to 1:10. You can also add distilled water to 4 grams of sodium hydroxide to make one liter 0.1N solution.

Use a pipette or burette to add 0.1N sodium hydroxide solution to 100 mL of the filter water, one drop at a time until the pH goes up to 7. You may use a pH meter or a pH indicator paper to monitor the changes in pH.

You can also use Phenolphthalein to monitor the pH during titration. Phenolphthalein will become red in alkaline solution however it is colorless in acidic environment. Every drop of Sodium Hydroxide will initially be pink, but it loses the color very fast. Continue titration to the endpoint of phenolphthalein. Endpoint is when the pink color persists for 30 seconds.

If you are using a 0.1N solution of sodium hydroxide for titration, every mL of sodium hydroxide represents one mL of 0.1N acetic acid (0.006 grams of acetic acid). Use the number of milliliters of 0.1N sodium hydroxide to calculate the amount of acetic acid in your entire solution.

Materials and Equipment:

List of material can be extracted from the experiment design.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.


After completion of each titration, use the number of milliliters of 0.1N sodium hydroxide to calculate the amount of acetic acid in your entire solution.

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.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.