Effect of Plants on reducing Particulate Matter (PM) levels in Indoor Spaces


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'''Effect of Plants on reducing Particulate Matter (PM) levels in Indoor Spaces'''</div>

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'''Gregorio Bonetti'''</div>
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'''Abstract'''</div>

4.3 million people die annually prematurely from illnesses related to indoor air pollution (WHO, 2014), and around 3 billion people are exposed daily to poor indoor air quality (Martin et al.,2021). The damaging health effects of air pollution, specifically particulate matter, stresses the need to know how plants can help reduce air pollutant levels. According to the National

Academies of Sciences in 2016, humans spend the majority of their time indoors which makes

it more likely that indoor PM exposure is a main contributor to the adverse health effects

caused by PM exposure. The aim of this experiment was to investigate the effect basil and

spider plants will have to reduce particulate matter levels in indoor spaces. Spider and basil

plants were put next to a desktop computer for one week each while the average PM

concentrations were measured daily for 15 minutes at an indoor testing site, PM was also

measured for one week without any plants. It was then found that the basil and spider plants

reduced the PM concentrations at the indoor site with the spider plants absorbing a greater

percentage of the PM (64.60%) than the basil plants (28.90%). Although both spider and basil

plants reduced the average PM concentrations, it is recommended to use spider plants to

reduce average PM concentrations as it was more effective.

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'''Introduction'''</div>

''1.1 Effects of indoor air pollution & particulate matter''

Air pollution is one of the biggest global health threats, causing around 4.2 million premature deaths in both rural and urban areas in 2019 (WHO, 2019). In the U.S., 600 million people were exposed to a dangerous amount of traffic-related pollution (Han & Naher, 2005). Around 4 out of 10 U.S residents live in counties with unhealthy levels of air pollution (American Lung Association, 2021). One of the most deadly types of air pollutants is particulate matter (PM). Indoor PM can be generated through cooking, combustion activities such as burning of candles, use of fireplaces, or kerosene heaters (WHO, 2023). Printers, copiers, consumer products (cleaning solutions, and air fresheners), and indoor dust all contribute to indoor particulate matter levels (WHO, 2023). The majority of Americans spend approximately 90% of their time indoors with 70% of that being at home (National Academies of Sciences, 2016). With the majority of Americans' time being spent indoors, exposure to indoor PM is likely to be a major contributor of adverse health effects caused by PM exposure (National Academies of Sciences, 2016). According to the American Lung Association long term exposure to PM2.5, particulate matter less than 2.5 micrometers in diameter, is related to risks of early death due to cardiovascular and respiratory diseases. Another study conducted by the American Lung Association revealed that, between 2000 and 2016, 68.5 million Medicare-enrolled adults in the United States found a 6-8% increase in risk of all-cause mortality for every 10µg/m3 increase in PM2.5.

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''1.2 Benefits of using plants to reduce PM''

Plants have a huge role in helping fight particulate matter pollution, as they absorb and remove particulate matter from the air. Leaves and other parts of the plant act as persistent absorbers of particulate matters (Zhou, 2015). Other research has shown that atmospheric dust over wooded areas can be 75% lower than over relatively non-vegetated areas (Lohr, 1995). A study in Chicago, IL, USA, said that if urban trees occupied 11% of the city area, they would remove 215,000 tons of PM every year (Mo, 2015). Trees tend to absorb more pollutants, including both types of PM (fine and coarse), than shorter vegetation (Mo, 2015). The benefit of using trees in highly polluted cities is that they act as physical barriers blocking pollutants from getting to people (Bennet, 2020). Studies show that the PM retention capacity of a plant leaves depends on their surface geometry, hair, epidermal features, plant age, and canopy structure (Zhou, 2015). Species that contain trichomes are considered more effective accumulators of PM (Mo, 2015). It’s important to know which plants and species are most effective at removing PM, and these plants should be used to help improve air quality.

''1.3 Properties of basil and spider plants''

Spider plants are considered “home” or indoor plants, and grow best between a temperature of 65 to 80 degrees Fahrenheit with a bright indirect sunlight (Braun, 2023). These plants also grow well under drained soil, and need to be watered regularly as well as fertilized once a month (Braun, 2023). According to a study by BalconGardenWeb, spider plants clean more than 95% of toxic agents from the air. Basil plants are best grown in outdoor spaces with adequate amounts of sunlight and shade, but can also be grown in indoor spaces (BalconGardenWeb, 2023). Basil plants also need to be well drained like spider plants, and also optimally grow with a soil pH of 5.5-7.5 (BalconGardenWeb, 2023). It’s important to make sure that the basil plants are never dried out completely (BalconGardenWeb, 2023).

''1.4 Purpose ''

'' ''The purpose of this experiment is to find the effect basil plants and spider plants have on reducing particulate matter levels in an indoor environment. It is expected that after the presence of the plants at the indoor site for one week the PM concentrations will decrease at the indoor site. It is also expected that since the spider plant has the widest surface area it will be the most effective plant at reducing the PM concentrations at the indoor site.

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'''Methods'''</div>

''Field Site Description ''

The experiment took place in an indoor environment next to a desktop computer under a desk. 3 plants were placed in an aluminum tray, and the air quality monitor was placed between the plants and the computer. The figure below shows the setup of the experiment. [[Image:Draft_Bonetti_579872458-image4.png|600px]]

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Figure 1: Demonstrates the set up of the experiment; important aspects are pointed out by arrows.</div>

''Experimental Design''

The research question was “What is the effect of plants on reducing particulate matter levels in indoor spaces?” The independent variable was whether plants were being used or not as well as the type of plant and the dependent variable was the PM concentration at the indoor site throughout the experiment. The control was the average PM concentration with no plants in the indoor environment for one week. Both spider and basil plants were tested for the same amount of time (1-week) with adequate amounts of water, and access to sunlight through a window. The PM concentration was measured every day during the one-week trial for each plant. It was hypothesized that the PM concentration will be lower when the plants are added to the environment.

''Subjects/Materials/Instruments''

:* Basil Plants (3)

:* Spider Plants (3)

:* PocketLab Air Quality Monitor

:* Metal Trays (2)

:* Water

''Protocols ''

'' ''First the materials were acquired which were 3 basil and spider plants as well as the PocketLab Air Quality Monitor. Then, the PM concentration of the indoor environment was measured prior to the start of the experiment. Once the concentration was measured 3 basil plants were added to the environment and monitored for 7 days. Over the course of the 7 days the PM and AQI, an air quality index used by the Environmental Protection Agency (EPA) to determine air quality, was measured along with the temperature and observations on the plants health. Plants were watered daily and had access to some sunlight through a window. After the testing period for the basil plants finished the plants were removed from the location and PM concentration was measured again 24 hours after the plants were removed. After the PM concentration was measured again 3 spider plants were added to the location. For another 7 days the plants were monitored and watered daily, and PM, AQI, temperature, and plant health observations were all recorded into a lab notebook and transferred to a Google spreadsheet. After the spider plant testing period concluded the plants were removed from the indoor site and average PM concentration was measured for another week with no plants.

''Statistical analysis''

''' ''' After all the data was collected and imported into a spreadsheet the rate of change for both spider and basil plant testing periods were calculated. In addition the daily average PM concentrations were recorded and depicted in a line graph showing both spider and basil plants. A two-sample t-test was conducted to calculate for statistical significance when comparing the average PM concentrations of the spider and basil plant testing period to the average PM concentration of the control (no plants).

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'''Results'''</div>

Figure #2 depicts the average PM concentrations for both the one week basil plant testing period and the one week spider plant testing period below.  [[Image:Draft_Bonetti_579872458-image2.png|600px|alt='Figure #2: Shows the average PM concentration in (µg/m3) for each day in the basil and spider plant testing period.'|Figure #2: Shows the average PM concentration in (µg/m3) for each day in the basil and spider plant testing period.]]

Figure #2: Shows the average PM concentration in (µg/m3) for each day in the basil and spider plant testing period.

During the Spider Plant testing period the highest PM concentration was 20.9µg/m3 while during the Basil Plant testing period the highest PM concentration was 57.1µg/m3. The lowest PM concentration was during the Basil plant testing period on Day 5 with a concentration of 1µg/m3 while the lowest PM concentration during the Spider plant testing period was 2.5µg/m3 on Day 1.

Figure #3 shows the rate of change for each testing period while Figure #4 shows the percent of PM absorbed for each testing period.

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Figure #3: Rate of change for daily intervals during each testing period </div>

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Figure #4: Rate of change for daily intervals during the Spider Plant testing period.</div>

The rate of change for the basil plant testing period was -2.06µg/m3 per day while rate of change for the spider plant testing period was -1.46µg/m3 per day. The percent of PM absorbed was 64.60% during the spider plant testing period, 28.90% for the basil plant testing period (with Day 7) and 85.60% for the basil plant testing period without Day 7.

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'''Discussion'''</div>

'' ''The effect of basil and spider plants on reducing PM concentrations in an indoor space has been summarized in the figures above. During the Basil plant testing period the average PM concentration (20.175µg/m3) was higher than the average PM concentration during the spider plant testing period (11.6375µg/m3). During this experiment both the spider plant and basil plant testing period showed a decrease trend from the initial PM concentration at the start of both experiments. This demonstrates that both the basil plants and spider plants have reduced the PM concentrations in the indoor environment with the spider plant reducing the PM concentration the most based on the average PM concentrations. With the damaging health effects of PM on human and environmental health it is important to know how effective plants are at reducing PM levels in the air.

A study revealed that spider plants absorb 95% of toxic agents or air pollutants from the air (Braun, 2023), while in the experiment when comparing the initial PM concentration and the average PM concentration the spider plant absorbed 64.60% of the initial PM from the start of its testing period while the basil plants absorbed 28.90% of the initial PM concentration from the start of its testing period. According to another study, trees or larger plants absorb more air pollutants than shorter vegetation or plants (Mo, 2015). Spider plants have a larger surface area than the basil plants and end up absorbing a greater percentage of its initial PM when considering the full one week testing period.

The data in this experiment revealed a decrease in the average PM concentration in the indoor location when there were spider and basil plants. Both the average PM concentration for the basil and spider plant testing periods were lower than their respective initial concentrations. The data in this experiment supports the expected outcome that the PM concentrations at the testing location will be lower when the basil and spider plants were added. However, the data does not support the hypothesis that the spider plants will have the greatest effect at reducing the PM concentrations at the location site as spider plants absorbed 35.70% of the initial PM while the basil plants absorbed 64.66% of the initial PM. When comparing both the PM concentrations with spider plants vs. no plants, and comparing the PM concentrations with basil plants vs. no plants both p-values were under 0.05. This means the data was statistically significant and not due to chance meaning that both the basil and spider plants were effective at reducing the PM concentration at the indoor site over the one week testing period.

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'''Conclusion'''</div>

'' ''The purpose of this experiment was to investigate the effect basil and spider plants would have on reducing PM levels at the indoor site. The major findings in this experiment were that both spider plants and basil plants overall reduced the average PM concentration at the location site with the basil plants absorbing 28.90% which is less than what the spider plants absorbed (64.60%). The hypothesis that the PM concentrations would be reduced at the indoor site once basil and spider plants were added is supported by the data. The hypothesis that spider plants would have the greatest effect on reducing PM levels at the indoor site is also supported by the data. The findings in this experiment were different to those of Mo, 2015 as in the experiment the basil plants absorbed less PM than the spider plants while in the study the plants with larger surface area absorbed more PM than the plants with shorter surface area. When compared to the findings from BalconGardenWeb the spider plants in the experiment absorb 95% of toxic agents while in this experiment the spider plants absorbed 64.60% of the air pollutants. To improve this experiment it’s important to address its limitations such as the fact that the readings from the air quality monitor fluctuate a lot as the monitor needs at least 15 to 30 minutes to settle into new air quality conditions. Also, the health of the basil plants started to decline towards the end of its one week testing period which could affect the results. Some recommendations for future research is to investigate the effects of plants on PM concentrations in an outdoor environment, or to measure the effect of plants on different types of air pollutants such as VOC’s, and CO2s. The damaging health effects of PM both indoor and outdoor stresses the significance of this research as it's important to know how plants can help prevent air pollution, one of the major global health threats.

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'''Acknowledgements'''</div>

''' '''Thank you Bethpage High School for approving this experiment, and providing the air quality monitor. More gratitude goes to the Bethpage Science and Research department for their help and guidance throughout the experiment. Another thank you goes to Mr. Pollatos, Mrs. Dulaney, and Mrs. Garvey for their assistance in the experiment. A final thank you goes to my mentor Zoe Chinda for all her help throughout my research.

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