An investigation of how air quality affects plant growth
Shaun Neo, Afif Azfar, Ong Jun Kai, Irfan Izzudin
School of Science and Technology, Singapore
Plant growth is affected by its surrounding environment. It can be used to measure air quality by their growth. We investigated the effects of air pollution on plant growth by burning charcoal, fire starters and paper to simulate polluted air. We applied this method to our experiment to discern what environment plants thrive in. To evaluate how well the plants grow, we have concurrently measured the height and growth of each plant in the different setups. The control plants grew to 22 cm in the end, as compared to the other plants exposed to less polluted and more polluted air, which grew 14.5 cm and 9.5 cm respectively. This indicated that plants, or green beans specifically, thrive in any environment with the least amount of air pollution. Graphs and tables were developed to be used as observation tools to inform people who are interested. Merits and limitations of results will be discussed as well as ways to further improve, develop and advance our experiment, as well as discuss potential directions for better research will be taken note of. Our experiment can be used to inform people in the agricultural business a recommended location for healthy plant growth. Our information can also be sold to companies for them to create a measuring tool to measure amount of air pollutants.
1.1 Background Research
Plant growth and distribution are limited by the environment. If any one environmental factor is less than ideal it will become a limiting factor in plant growth (University of Arizona, 1998). All external conditions and influences affecting the life and development of an organism. (Stephen W. Broome, nd).
In this study, we aim to use charcoal and other burning materials which will be used to affect the different air qualities in each set-up. Pollution is the presence or an introduction into the environment of a substance which has harmful or poisonous effects. Annual losses of plant life e.g. crops, trees that are caused by air pollution are estimated to be worth more than a billion dollars (Earth Observatory, nd).
The effects of pollution on plants include mottled foliage, “burning” at leaf tips or margins, twig dieback, stunted growth, premature leaf drop, delayed maturity, abortion or early drop of blossoms, and reduced yield or quality. The pollutants also affect how the plant grows and develops, showing a change in colour of a leaf in a plant (Eduardo Zeiger, 2006). So, when the air quality is poor, there maybe a reduction in growth, and after suffering recurrent injury, they will die. It is hypothesised that if the air quality is poor, plants would not grow as much as when compared to an area with a richer air quality.
There are many factors that affect air quality, such as city size, city location, land topography, soil moisture, nutrient supply, time period, species or variety of plants. Damage caused by air pollution is usually most severe during warm, clear, still, humid weather when barometric pressure is high. Accumulation of toxicants take place near middle atmosphere when warm air aloft traps cooler air at ground level. This is called air inversion.
The burning of hydrocarbons in motor vehicle engines gives rise to Carbon Dioxide (CO₂) , Carbon Monoxide (CO), Sulfuric Dioxide (SO₂), Nitric Oxide + Nitrogen Dioxide (NOx) and sometimes, in varying proportions, Ethylene (C₂H₄). Industrial plants, such as chemical works and metal-smelting plants, release SO₂, Hydrogen Sulfide (H₂S), Nitrogen Dioxide (NO₂), and Hydrogen Fluoride (HF) into the atmosphere.
Photochemical smog is the product of chemical reactions driven by sunlight and involving NOx of urban and industrial origin. Ozone (O₃) and Peroxyacetyl Nitrate (PAN) are being produced in these reactions and they can harmful and injurious to plants and other life forms. Hydrogen peroxide (HO), another potentially injurious molecule, can form by the reaction between O₃
and naturally released volatiles (terpenes) from forest trees (Eduardo Zeiger, 2006).
The responses of plants to polluting gases can also be affected by other ambient conditions, such as light, humidity, temperature, and the supply of water and minerals. Experiments aimed at determining the impact of chronic exposure to low concentrations of gases should allow plants to grow under near-natural conditions.
In the experiment, we controlled the amount of air pollution by varying the amount of materials used to burn. We used the same type of burning materials, plants and other constants to ensure a fair and accurate experiment is conducted. Our results proved our hypothesis, which indicated that plants thrive under purer air quality.
1.2 Research Question
An investigation of how air quality affects plant growth.
If the quality of the air is poor, the plants will not grow as much as when compared to an area which has a cleaner air quality.
1.3.1 Independent variable(s)
Quality of the air / Amount of air pollutants in the air. (This will be measured by amount of flammable materials burnt)
1.3.2 Dependent variable
The growth of the plants measured in centimeters.
- Type of seed
- Type of soil
- Brand of seed
- Amount of seeds per jar
- Amount of soil per jar
- Volume of water added to each jar per day
- Distance between each planted seed
- Type of charcoal
- Size of bell-jar
- Amount of sunlight
- Time between measurements
Equipment ordered from school
Green bean seeds
Mini aluminium trays
Figure 1 : Setup with high amount of pollutants
Figure 2 : Setup with low amount of pollutants
Figure 3 : Setup with no pollutants
1. Fill each pot with the same amount of soil (150mℓ) and water (4mℓ).
2. Place 4 seeds exactly 3 (cm) apart. This is so that the plants will not get over-crowded to ensure reliability of the results. Name each cup setup 1, setup 2 and setup 3.
3. Place the set-ups in the respective bell jars.
4. Measure the amount of combustible material (g) to be put in each set-up. Then add the materials into the bell-jar and start the burning.
5. Place the burnt material (69g) above an aluminium disposable tray for setup 1. For setup 2, place burnt material (28g) in the bell jar on the aluminium tray.
6. Let the fire burn for a few minutes, because there will be little oxygen inside the bell jar. Once it has burnt enough, place the plant with the aluminium tray together and quickly cover it with the bell jar. Do the same for set up 2.
7. Begin the measurement of the plants growth in (cm) per day. Plants must be watered with the same amount of water each day, per (mℓ). Plants must also be in the same location to ensure that the amount of sunlight received by each bell jar is the same to reduce an effect on the results.
8. After collating all the data and looking at the results and doing an analysis, we can find out whether polluted air really affects the growth rate of the plants and by how much.
9. Repeat the experiment again to make sure that the growth of the plants are not due to human error, and that the quality of air actually affects the growth of plants.
2.4 Risk Assessment and Management
1. A risk while doing the investigation is burning the charcoal in the bell jar. This is because the air may escape from the container that we are keeping it in and if there are people who have lung problems in the lab, may experience some breathing difficulty choke to death. A safety precaution is to wear masks when handling with the polluted air. Also, have a first aid kit on hand in case of accidents. Another way is to cover the top of the bell jar with N95 masks as it can prevent pollutants from escaping the jar and let the oxygen particles in and out of the jar. If burning the charcoal with matches, the match burns very quickly and it might burn the finger, so hold it perpendicular to the surface.
2. A risk while doing the investigation is getting burned while burning the charcoal. Since we are going to be handling with fires to make the pollution, someone might get burnt in the process. To prevent this from happening, always stay a distance between the fire and have the first aid kit ready in case someone gets burned. Also, do not burn in the lab because the fire might spread, thus we should have a fire extinguisher nearby. We should also let only one person handle the fire to prevent any confusions and accidents.
3. A risk while doing the experiments that the bell jars may break if not handled carefully. The shattered glass may hurt someone if it is not cleaned up fast. To prevent this from happening, make way for the person who is holding the glass jar, and if the glass breaks, have a first aid kit on hand. Also, clean up the glass so it does not injure other people. Also it will be safer if 2 people carry each bell jar instead of 1, this will decrease the chances of the bell jar dropping and shattering, which may cause harm to surrounding property or members of the team.
4. A risk while doing the investigation is that when the team is burning the material to create the smoke, the ash from the fire might escape the funnel if not handled properly and could burn surrounding members. To prevent this from happening we should always be aware of our surroundings and make sure that there is no leakage before we begin the burning.
5. A risk while doing the investigation is that the team may shatter the flammable liquids such as the ethanol, which if spilled and caught on fire may cause severe burning and damage of equipment and may also hinder the investigation. To prevent this from happening, we should handle flammable materials with great caution and only take them with the permission and guidance of adults like the science teacher and the lab manager.
2.5 Data Analysis
1. After completion of the burning process, we would remove the plants from the jars. The team would then measure the height and growth of each plant with a ruler. We would measure all the plants in the same setup and take the average height to get a more reliable result, incase the growth is extremely different for the same setup.
2. After that we would find the average growth of each plant for each setup and record the growth for each setup. We take the average to ensure that our experiment is precise and accurate, and allows us to predict the most probable outcome of the experiment.
3. If setup 1, which is the set up with the most amount of air pollutants, grew the least and setup 3, which is the control exposed to normal environment, grew the most, it proves our hypothesis.
3.1 Experiment 1 results
3.2 Experiment 2 results
3.3 Special observations
During the experiment our team notices that some plants were actually drooping and some died. Although the water poured into the three pots were equal, there were other factors that could have killed the plants. Such factors would be the amount smoke prevents the plants from getting enough sunlight to produce food. Another factor noticed was that the heat given off by the smoke might be of a too high temperature and resulted in the plants dying.
4.1 Key findings
Plants thrive in normal conditions and grow at a slower pace in hazy conditions as compared to plants in a normal environment. This could be shown by the obvious difference in rate of growth and final growth. The plants grown under extremely polluted air grew at a much slower rate than the plant that grew under normal air quality.
4.2 Explanation of key findings
Plants can be affected by the physical factors of its environment. Polluted air will affect the environment, and cause the plants to grow or react in a different way than in normal air conditions. As hazy conditions make the surroundings rather dark, only a small amount of light can pass through when it is very hazy. With less light, the plant’s stomata will react in a way that when the surrounding conditions looks like the night, the plant will close its stomata, which will hinder the plant’s growth. As haze scatters it absorbs solar radiation, which reduces the sunlight reaching the surface by a certain percentage, thus reducing amount of light absorbed and nutrition produced, which in turn hinders the plants growth. It will partially shut its stomata and will not allow much oxygen or carbon dioxide to enter, at the same time reducing the amount of sunlight absorbed by the plant, which reduces the rate of photosynthesis. With the haze around the plant all day long, the plant will shut its stomata at a partial amount as some light can pass through the haze. This could be one reason that affects the plant growth.
Haze affecting many parts of the world are aerosols composed of solid and liquid particles of varying sizes. The major pollutants that contribute to outdoor pollution are, carbon dioxide, carbon monoxide, sulfuric dioxide, nitric oxides, and in some rare cases ethylene. While the pollutants that contribute to indoor pollution are radon, formaldehyde, nitrogen dioxide and carbon dioxide.
Plants and humans both respire, and these particles that float in the air are taken in their respiratory systems, which will hinder their body processes. It affects the plant in a similar way too. In respiration for both plants and animals, the sugar, or the photosynthates, back into energy for growth and other life processes, or the metabolic processes. Photosynthates are combined with oxygen releasing energy, carbon dioxide, and water. A few important pollutants that affect plant growth are nitric oxide, zone, and sulfur dioxide.
Nitric oxide are formed naturally by bacteria in the soil. Nitric oxide by itself is non-toxic but can be converted to nitrogen dioxide. At high concentration levels, nitrogen dioxide can damage plants and can reduce growth and yield. In combination with ozone or sulphur dioxide, it can even cause damage at lower concentration levels. As it is one of the components of smog, it can increase susceptibility to respiratory infections.
Ozone is formed during photochemical smog in the atmosphere. The air does not move and can be trapped to the earth’s surface forming smog and affect respiratory and breathing problems. Ozone enters the plants through the stomata, just like other gases, it dissolves in water within the plant. Once that happens, a variety of problems is being created. Cell membranes start to be leaky, as ozone has the ability to interact with lipid components, the process of photosynthesis is slowed and hinders the growth of plants. Plants affected by ozone are more susceptible to pests, diseases and drought.
Sulfur dioxide is a primary element in acidic precipitation. It impairs the respiratory system making it less resistant to respiratory illnesses. Long term exposure of low concentration of sulfur dioxide can cause the plant to have the inability to fight against bacteria or foreign particles.
4.3 Evaluation of hypothesis
Based on our results collected, our hypothesis was proven. This is because the plants exposed to the polluted conditions grew at a much slower rate in comparison to the plants left in cleaner air.
4.4 Areas for improvement
1. Instead of using cotton wool to cover the top of the bell jar, we could use N95 masks, or cut out certain sections of it to cover the top, as the masks can prevent pollutants from escaping the jar at the same time allowing particles like oxygen, carbon dioxide in and out of the masks.
2. To prove that our results are reliable, we should not use only one type of seed, we should use a variety of seeds. This can make our findings for reliable and accurate, so we can find out whether the polluted air affects all types of plants, or only certain plants.
3. We can change the measurement unit for the soil from ml to grams. This will help to reduce human error as when measuring in ml, there may be air pockets within the soil that has been taken, thus the actual amount of soil may be lesser than others. Instead, we should use grams to measure as this would accurately measure the mass instead of the level of soil in the beaker, thus creating a more fair experiment.
4. We could use a flatter aluminium tray so that we can reduce the air pollutants from escaping the jars. This is so that the results of the experiment will be more accurate, as well as so that we can reduce human error of putting moist cotton wool to prevent the pollutants from escaping the jar bell.
5. We could also use either larger jar-bells, or smaller pots so that the pots and the tray holding the burning materials would be able to fit properly in the jar-bell, and reduce spilling of the ash, or spilling of the soil. Also, this will help to not tilt the pot, so that the plant will be able to grow straight and not affect the accuracy of the results of the experiment.
6. When adding soil or water to the set-ups instead of measuring the amount through volume, measuring the amount through grams would be a more accurate. As soil or water particles can be compressed, thus increasing the volume of soil, which in turn may affect the growth of the plants, hence making the results unreliable or inaccurate.
5.1 Summary of findings
From the results, we can conclude that plant growth is affected by the condition and amount of air pollutants. Our control, which was exposed to normal air, grew to 22 cm at the end of the experiment. The plants that grew under slightly polluted and extremely polluted air, grew 14.5 cm and 9.5 cm respectively. This indicates that plants thrive under an environment with the least amount of pollutants. The air pollutants will reduce amount of light that can be used for photosynthesis, thus rate of growth will be slower.
5.2 Practical Applications
From our experiment, we found out that plants cannot grow or thrive in hazy conditions simulated in our experiment. Our team can recommend that for people growing plants in regions prone to Haze such as Singapore to keep their plants in a closed environment with non-polluted air. This will help to keep the plants healthy.
As hazy conditions affect plant growth, farmers can use this research and apply it too. They can know how much their crop can yield in a certain amount of pollution or whether it is healthy to plant crops in a certain area.
As haze contains sulphur dioxide, plus it is a primary element in acidic precipitation. Scientists can calculate the sulphur dioxide concentration in the air and can predict and understand more about acid rain. Farmers can be informed whether their location is prime for plants to grow, and leave them to make the choice to move or remain.
5.3 Areas for further study
Areas that can be researched into further depth are what could be burnt such that our experiment would be more effective such that the results from the experiment would be clearer. For instance, we could burn wood to better simulate the haze environment since the cause of the haze is due to the burning of wood.
Areas that can be further studied and researched into greater depth could be what kind of burning materials create the most haze. For instance, we could burn another material that creates a constant flow of smoke and is easier to burn.
Areas that can be further studied and researched are what kind of fuels when burnt creates the air pollutants that affect plant growth the most. For instance, we could test which fuels, when the same amount of each fuel is burnt, creates air pollutants that stunt the growth of the plants the most.
Areas that can be further studied and researched is what species of plants are least affected by its environmental factors. We can experiment to find out whether these species can thrive no matter the environment and investigate why. For instance, we could redo our experiment, but this time have a greater variety of plants, and test which plants are most self-sufficient and durable to the quality of air.
Areas that can be further studied and researched is what is the specific pollutant that is caused by burning flammable materials that directly affect the growth of the plant, aside from reducing the amount of light received. For instance, other advanced scientists could burn the same materials that we used, and separate each component of the air pollutants, and experiment with the components on which directly affect the growth of the plants and why.
Areas that can be further studied is using the information from the experiment above, scientists could develop a certain chemical to spray around the plants, that will reduce or cancel out the effect of the pollutants that stunts the plants’ growth, hence allowing plants to thrive with any air quality.
Our team would like to express our gratitude to our science teacher, Mr Charles Low in assisting and guiding us in our Project. If not for him, we would not be able to complete our project as he assisted us in the burning the charcoal. Our team would also like to thank Ms Su, The Lab Manager for providing us with the materials to complete our project.
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