The Efficiency of Vertical Plants’ Types and Catchment Areas for Absorbing Carbon Dioxide in Ambient Air

The Indonesian government has set regulation, whereby 30% of the city region should be repurposed as green open spaces to mitigate climate change. However, several cities have not attained this because of a lack of land availability. One of the potential solutions is using of vertical gardens that can absorb CO2 in limited areas. The study aims to determine the CO2 absorption by several vertical plants at different sizes of planting areas and elevations. The study was conducted on three sites in the Department of Environmental Engineering Institut Teknologi Sepuluh Nopember under various circumstances. The study variables included: (i) plant species, i.e. Antigonon leptopus, Epipremnum aureum, and Vernonia elliptica, which were grown in a 55×40×37cm box reactor, (ii) different catchment or planting areas (25%, 50%, and 75% of the reactor’s surface area), as well as (iii) elevations (0 m, 4.5 m, and 8.5 m above ground level). A single reactor was used as control variable. The parameters under observation were CO2 level, temperature, and light intensity recorded hourly from 06.00 a.m. to 06.00 p.m. The capability of the plant to absorb determined by the difference of Net-CO2-Con. The result shows that the more plant’s catchment areas positively contribute to the reduced CO2. The 75% of Antigonon leptopus potentially decreased by 314 ppmCO2/day, while 50% and 25% of it only decreased by 271 ppmCO2/day and 119 ppmCO2/day. Antigonon leptopus is the most efficient plant in its light tolerance, compared to other plants. Antigonon leptopus showed the highest CO2 uptake value at 314 ppmCO2/day, while Epipremnum aureum and Vernonia elliptica displayed 126 ppmCO2/day and 184 ppmCO2/day respectively. However, the CO2 uptake capability of each plant at different elevations was subjected to bias due to coverage by buildings and canopies. This altered the intensity of sunlight and interfered with plant assimilation, ultimately impacted the uptake capability of CO2.


Introduction
The increase in population has led to a rise in population density [1].This surge in population has reduced the availability of land for utilization.Moreover, highly populated areas have experienced a boost in CO2 emissions due to increased transportation and fuel consumption activities [2].The natural carbon cycle is disturbed through the transfer of carbon to geological reservoirs, such as the movement of carbon from fossil fuels to active terrestrial storage pools [3].The rapid rise of CO2 levels in the atmosphere has created a discrepancy in the distribution of CO2 between the oceans and land.This 1307 (2024) 012002 IOP Publishing doi:10.1088/1755-1315/1307/1/012002 2 augmented concentration of CO2 has the potential to intensify global warming by enhancing the greenhouse effect [4].
Implementing green open spaces by optimizing existing land use is an effective strategy for reducing CO2 levels.Green open spaces are areas of land used for the growth of plants, including naturally occurring ones and deliberately planted species.They play a key role in moderating atmospheric conditions, producing oxygen, and acting as a sink for water, air, and soil pollutants [5].The scarcity of land in Indonesia has presented obstacles to establishing green spaces [6].Although some Indonesian cities have satisfied the standard for open green spaces of at least 30% of urban or suburban areas (with a minimum of 20% designated for public open space use and 10% for private open space use), there are still several localities that fall short of meeting these requirements.
One example is the Kota Bogor.By 2021, Kota Bogor only had 2,031.66Ha or about 17.14% of green open spaces area.[7].On the other hand, Kota Malang achieved only 18.14% of green open spaces by 2019 [8].The densely populated residential and commercial areas of some cities in Indonesia have hindered the allocation of land for urban green spaces such as urban forests and parks.The problem of access to private green space has also been exacerbated by the low number of houses with gardens [9].Using plants that can absorb CO2 while minimizing land use is one option that should be considered.
Vertical gardens are vegetated surfaces on walls, either rooted in the ground or incorporated into wall materials or panels [10].They are an effective solution for increasing green open spaces in urban areas [5].By efficiently circulating and absorbing fumes, dust, and CO2.They are more effective than trees in reducing air pollution [11].CO2 can be utilized by any plant that has chlorophyll.This process of photosynthesis converts CO2 into glucose and O2, resulting in a decrease in CO2 levels.Photosynthesis can be affected by both internal and external factors.The genetic composition of the plant determines the internal factors, which include the size and number of leaves, mesophyll cells, chloroplasts, and chlorophyll concentrations.Plant growth and other biological processes depended highly on leaf size, such as leaf surface area, dry mass, and length [12].The environmental conditions of the plant's environment influence the external factors that affect plant growth.These factors include water availability, CO2 concentration, sunlight intensity, and temperature.
According to Regulation 14/2022 of the Indonesian Ministry of Agriculture and Spatial Planning, the flora selected for the vertical garden installation must not damage the building structure.It should thrive in high light and temperature conditions, withstand windy conditions, and be easy to maintain.The flora should be locally adapted to the existing ecosystem and serve the purpose of absorbing pollutants, reducing noise levels, attracting wildlife, and enhancing the appearance of the building.
Three plant species (Antigonon leptopus, Epipremnum aureum, and Vernonia elliptica) are used based on these considerations.On a 1 m 2 wall panel, Antigonon leptopus has been found to absorb 15 ppm of CO2 in 10 seconds [13].Epipremnum aureum has been shown to effectively reduce indoor particulate matter, reducing PM2.5 concentrations from 250 μg/m to 130 μg/m within 20 minutes [14].Vernonia elliptica has been found to absorb suspended particulates and oxygen in nitrogen and sulfur in addition to its thermal comfort benefits [16].
No further research or literature has been found regarding the ability of Epipremnum aureum and Vernonia elliptica to absorb CO2 from outdoor air.Though, these plants have heavily been utilized in Indonesia, on building walls or along roadsides.The CO2 absorption capacity of vertical plants at particular circumstances in various elevations also has not been examined.Whether this influences the absorption ability of plants in a vertical garden is still unknown.The absorption value of CO2 emissions is calculated using the cumulative concentration equation (Net_CO2-Con).Plants assimilated CO2 throughout the experiment, leading to a decline in concentration over time.Consequently, the numerical analysis of the curve area could be used to determine the quantity of CO2 uptake.

Preliminary Study
The study utilized Antigonon leptopus, Epipremnum aureum, and Vernonia elliptica plants in their generative phase.It found that plants in the generative phase exhibited increased photosynthetic capacity and a lower transpiration rate [16].Each plant was placed in a 55×40×37 cm reactor box contained with soil and organic fertilizer as a growth medium.To fill the box volume of 55×40×10 cm, approximately 4 kg of soil:fertilizer (1:1) was used for each reactor.This combination yields favorable plant growth results [18].The organic fertilizer utilized comprised charred husks, compost, and cocopeat.
A species of plants was planted in each reactor at 25%, 50%, and 75% of the reactor bed area.The number of plants required in figure 1 and table 1 was calculated by dividing the total planted area by the area that could be covered by a plant.In this study, the control variable was a reactor without any plant growth.The ten reactors were placed at different elevations across each study location.I.e., the workshop yard area (0 m), the western corridor of the second floor (4.5 m), and the eastern corridor of the third floor (8.5 m) Department of Environmental Engineering, ITS, Surabaya.
The variables examined include variances among plant species (Antigonon leptopus, Epipremnum aureum, and Vernonia elliptica), the CO2 catchment areas or planted areas (25%, 50%, and 75% of the reactor bed area), and the elevations of each reactor installation (0 m, 4.5 m, and 8.5 m in height).The variables were analyzed to ascertain their contribution to the reduction of CO2.Before the study, seven days of acclimatization based on previous studies were performed [19].

Sampling and Data Collection
The primary data collected were CO2 concentration, sunlight intensity, soil moisture content, and temperature.Each variable in the reactor was measured using the same parameters.These parameters were external factors that influence photosynthesis.Additionally, by utilized these parameters, it could be observed whether varying elevations exhibit different results in light intensity and temperature, consequently impacting the outcome of photosynthesis.CO2 concentration, sunlight intensity, and temperature were measured every hour for 13 hours (06.00 a.m. to 06.00 p.m.) when the Hill reaction occurred.Sampling was carried out over nine days according to the Krecjie and Morgan method with the population was the average annual number of rainy days from 2010 to 2020.[20].Sampled begins by inserting a sensor connected to the CO2 meter (10 cm into the reactor through a small gap in the center of the reactor's plastic cover).CO2 concentration and temperature readings were recorded for one minute and the average value was used.

Light Intensity
Measurement.The SM206 solar power meter was used to measure sunlight intensity.The measurement process involved directing the sensor towards the incoming sunlight and detecting the captured light as energy through the photocell, which then transformed into an electrical current.The amount of current generated increased with the amount of light captured [21].

Soil Moisture Measurement.
The Soil Moisture PH Meter Tester VT05 was used to detect moisture in the soil.This device implemented with a sensor that passes an electric current through the soil.Excess soil moisture reduced its electrical resistance and made it more conductive, while dry soil had high electrical resistance and was not as conductive [22].Soil moisture was measured by inserting the soil tester probe into the soil until it was completely covered.Measurements were taken daily before the beginning of the research.The soil moisture was kept constant at 80% in all reactors.Large plants generally absorb CO2 better with 80% moisture [23].

Cumulative CO2 Concentration Calculation
The cumulative value of CO2 concentration was determined using the Net_CO2-Con equation which calculated area under the integrated curve [24].To calculate the rate of CO2 concentration, the analysis involved differentiating the concentration over time (∆C/∆t).∆C referred to the difference between the current CO2 concentration (Cx) and the beginning CO2 concentration (C0), while ∆t is the time difference between the two measurements (tx -t0).A curve equation was calculated using the rate of change of CO2 concentration (∆C/∆t) (y) over time (x).The integrated CO2 concentration rate curve equation yielded the value of CO2 concentration (KCO2) which represented the area beneath the curve of the rate of change in CO2 concentration.A negative KCO2 indicated a reduction in CO2 concentration within the reactor, while a positive KCO2 denoted an increase in CO2 concentration.This curve indicated the ability of the plant to capture CO2 [24].The CO2 uptake of the plant was determined by subtracting the overall CO2 concentration in the reactor containing plants from that in the control reactor.To investigate the effect of independent variables (plant type (x1), plant catchment area (x2), and plant elevation (x3)) on the dependent variable, CO2 reduction (y), a statistical analysis was conducted.This study conducted across three locations, each with varied elevations resulted in different characteristics.The workshop yard area (at 0 m elevation), was exposed to morning sunlight.As the day approached noon, the reactor was not directly exposed to sunlight due to the presence of a tree canopy.However, the highest average figure for incomed light intensity was recorded at 09.00 a.m., measured at 333.2 W/m 2 .As the afternoon progressed, some amount of sunlight was again exposed to the location.Meanwhile, at an elevation of 4.5 m, on the second-floor corridor near the western staircase of the ITS Environmental Engineering Department, the reactor was exposed to direct sunlight under certain conditions.It was shaded during the daytime by the building's shadows.However, in the afternoon, the sun beamed directly on the plants.At 03.00 p.m., the sunlight intensity reached its maximum with an incident light of 504 W/m 2 .

Result and Discussion
Elevation of 8.5 m situated in the third-floor corridor adjacent to the eastern staircase of the ITS Department of Environmental Engineering.Direct sunlight was available throughout the day, although it might be obstructed by a canopy under certain circumstances.This position experienced full sunlight from morning to evening, and at midday (around 01.00 p.m.), the sunlight intensity measured 638 W/m2.

CO2 Concentration Change Results
CO2 concentration was measured for 13 hours daily, from 06.00 a.m. to 06.00 p.m. Measurements took nine days to obtain accurate CO2 concentration results.The results plotted as a graph depicted the concentration of CO2 each day (y) per hour (x).A polynomial auxiliary line was added to facilitate data determination by identifying the CO2 value closest to it.To avoid the impact of erratic weather, we did not use average values, which tended to reflect fluctuations and failed to represent the whole data.Interpolation was used to obtain functions based on given data points.Photosynthesis influenced by a range of factors, such as light, CO2, temperature, water, chlorophyll concentration, photosynthesis accumulation, leaf gas diffusion resistance, and protoplasmic factors [25].The data displayed the CO2 concentration in different catchment areas (75%, 50%, and 25%) with the nearest point to the second-order polynomial regression line (R 2 value close to 1) shown in figures 4, 5, and 6.An R 2 value close to 1 signified an even more precise impact [26].This data was analyzed further using table CO2 concentrations could decrease in the control reactor due to the carbon cycle in the soil, led to its partial absorption.The soil has played a crucial function in the impact of climate change by absorbing CO2, mainly as organic matter, which was subsequently stored in the soil [27].Nevertheless, the absorption rate was not significant.7 showed that each reactor had different CO2 absorption abilities, which varied without following a set pattern.In the morning, the samples were similar to the control due to lower sunlight intensity, and photosynthesis inefficiency resulted.Residual CO2 generated by plant respiration during the night continued to be present and contributed to the CO2 concentration in the reactors.The CO2 concentration experienced a decrease from 07.00 a.m. until it once again surpassed the control CO2 concentration at 03.00 p.m.At 11.00 a.m., the concentration of CO2 in Antigonon leptopus with a catchment area of 75% reduced to 258 ppm at an elevation of 0 m.It decreased to 308 ppm at an elevation of 4.5 m and reached a minimum of 223 ppm at an elevation of 8.5 m.Plants were capable of efficiently reduced CO2 through photosynthesis during the daytime.At 11.00 a.m., a substantial amount of carbohydrates was founded in the leaves where photosynthesis occurred efficiently [28].

CO2 Concentration in Each
Antigonon leptopus situated at an elevation of 4.5 m not experienced a significant decreased in CO2 concentration compared to other sites.This was due to limited exposure to sunlight, which shaded the plant species.Conversely, this significant decreased in CO2 concentration founded at an elevation of 8.5 m where there is sufficient exposure to sunlight.This indicated that this plant species thrives in areas with high levels of sunlight.
After reached the point of saturation for daytime CO2 absorption, the plant's capacity to absorbed CO2 decreased, resulted in an elevation in the graph.At the point of peak light intensity, maximum CO2 saturation occurred.However, surplus energy absorbed from increased sunlight is not utilized efficiently, led to a decline in the efficiency of photosynthesis II.This, in turn, resulted in photoinhibition of photosynthesis [29].During the daytime, the CO2 concentration in the control was higher than that observed in the plant reactor.The vegetation could decrease CO2 concentration, however, plant respiration caused an increase in CO2 concentration during the late afternoon until nightfall, surpassed the control reactor.Insufficient sunlight reduced the activity of enzymes that are responsible for photosynthetic carbon assimilation.As a result, plant carbon assimilation was restricted, led to a decrease in photosystem II photochemistry's effective quantum yield [29].The planting of over 75% of the bed reactor area with plants resulted in a significant reduction in CO2 concentration.This observation implied a connection between the area of leaves, the amount of chlorophyll present, and the photosynthetic efficacy.The observation was supported by the point situated at the bottom of the curvilinear plot.The discoveries implied a plausible association between plant configuration and photosynthetic productivity.The CO2 reduction in Figure 8 varied at different times.For instance, the Epipremnum aureum reactor, with a catchment area of 75% at an elevation of 0 m, achieved the minimum CO2 concentration of 304 ppm at 09.00 a.m.At 4.5 m elevation, the concentration decreased to 330 ppm at 11.00 a.m.Subsequently, at the same time at an elevation of 8.5 m, the plant attained a CO2 concentration of 328 ppm.It should be noted that each plant had a unique time for photosynthesis.Epipremnum aureum was discovered to thrive more effectively in areas with a sunlight intensity of 0 m elevation, compared to areas with elevations of 4.5 m and 8.5 m.Plants positioned at 4.5 m experienced a lower level of sunlight, whereas those at 8.5 m were exposed to an excessive amount.

CO2 Concentration in Each Epipremnum aureum Reactor at 0, 4.5, and 8.5 m Elevations
The Epipremnum aureum curve closely followed the control curve line, indicated that these plants are unsuitable for outdoor use.One significant factor was their inability to tolerated prolonged exposure to high temperatures and sunlight.At an elevation of 8.5 m, Epipremnum aureum appeared paler than at other elevations.Moreover, within the reactor, temperature could reach up to 45°C due to confined conditions and heat exposure.Indoor CO2 levels were reduced by 1,058 ppm and 1,036 ppm, respectively, when six Epipremnum aureum pots were incorporated and exposed to light intensities of 1000 lux and 2000 lux.Epipremnum aureum with 75% catchment demonstrated better performance than E. aureum with 50% or 25% catchment area.Based on elevation, this plant effectively decreased CO2 at an elevation of 0 m from the ground surface due to moderated incomed sunlight [14].The efficacy of CO2 reduction was lower and more variable in Vernonia elliptica as compared to Antigonon leptopus, wherein the latter exhibited better performance in reduced CO2 levels, outperforming Epipremnum aureum.The CO2 level reduction process was initiated at 07.00 a.m. in Vernonia elliptica and demonstrated less significance at 06.00 a.m. as compared to the control condition.The decrease continued throughout the day until approximately 11.00 a.m. or 12.00 p.m. when it began to steadily rise.Figure 9 illustrated the decreased until an optimum level for photosynthesis was achieved.Subsequently, CO2 levels rose in the afternoon and evening due to diminished photosynthesis and increased plant respiration.Plants generated harmful O2 radicals under high light intensities, which impeded the Light Harvesting Complex (LHC) and led to photoinhibition.Under low lighting, both the effectiveness of photosynthesis and stomatal conductance decreased.This, in turn, resulted in an increased in CO2 concentration within the cells of the leaves [30].

CO2 Concentration in Each
The plants attained the maximal reduction rate at a 75% catchment area.For the entire day, the point on the curve shown in figure 9 at the 75% catchment area exhibited a greater deviation from the control reactor in comparison to the 25% and 50% catchment areas.Consequently, the enhancement of plant numbers led to greater CO2 reduction.This plant flourished in locations that received complete exposure to sunlight, such as at a height of 8.5 m.The study presented a comparison of CO2 concentration levels between the control and plant reactors, with an appropriate separation between them.

Cumulative Value of CO2 Concentration
The CO2 concentration was measured over a specific time and fluctuations were observed.The rate of CO2 concentration was determined using a differential calculus approach by differentiating the concentration of CO2 against time (∆C/∆t) [23].∆C indicated the distinction between the CO2 concentration provided and the initial concentration (Cx -C0).∆t represented the difference in time between the study and the initial study time (tx -t0).These calculations enabled the creation of an equation that displayed the relationship curve between the rate of CO2 concentration (∆C/∆t) (y-axis) per time (x-axis).The entire KCO2 value was ascertained by integrating the area under the curve.A negative (-) KCO2 reduction value signified a decreased in CO2 concentration and a positive (+) value indicated an increased.A KCO2 value of 0 indicated equal reduction and production of CO2.The CO2 concentration uptake value of the plant calculated by the difference between the CO2 concentration in the reactor-containing plant and the concentration in the control reactor.This method allowed for the precise determination of CO2 uptake by each plant.The control condition revealed a slight decreased in CO2 due to carbon sequestration by the soil.
Based on the graph presented in figure 10, the study concluded that Antigonon leptopus is the most effective plant for CO2 absorption, with a catchment area of 75%.The optimal coverage area for CO2 reduction was also 75%, followed by 50% and 25%, respectively.Therefore, the number of plants used significantly impacted photosynthesis.Greater plant diameter and width led to higher CO2 uptake [31].Table 5 demonstrated the efficiency of each plant reactor in reducing CO2.[33].Due to its high APTI, this plant was highly recommended for use in the Vertical Greenery System (VGS) and was capable of reduced CO2 by up to 15 ppm per 10 seconds within a panel area of 1 m 2 [13].From the research concluded that both internal and external factors of photosynthesis had an impact on CO2 reduction.Detailed explanations presented below.To investigate this, the study positioned plants at differing elevations.However, the differences between elevations were not significant and therefore the air temperature and humidity conditions were similar.The sole discernible difference resulted from the degree of incomed light, which was influenced by the surrounding buildings and canopy of trees.This disparity produced various photosynthetic outcomes.Antigonon leptopus displayed proficient CO2 reduction at an elevation of 8.5 m.The preceded phenomenon was also witnessed in Vernonia elliptica.Conversely, Epipremnum aureum plant were more adapted to conditions at 0 m elevation.
Certain plants thrived in both shaded and unshaded environments.Nevertheless, Antigonon leptopus and Vernonia elliptica were better suited for planted in unshaded areas.Epipremnum aureum flourished in areas that were covered by shade but still exposed to the sun for a specific period.Epipremnum aureum, located at an elevation of 8.5 m, was exposed to uninterrupted sunlight, which raised the temperature of the reactor and resulted in leaf scorching.Generally, this plant preferred moderate light conditions and optimal temperatures of 22-26°C for ideal growth [33].Epipremnum aureum flourished in a moderately lit environment, where it received sufficient brightness without exposure to directed sunlight.
Excessive light intensity accelerates the process of chlorophyll photooxidation, which hampers the plant's photosynthesis capabilities.Conversely, lower light intensity limits the photosynthesis process and promotes the depletion of food reserves.In addition to light intensity, the process of photosynthesis is also sensitive to temperature.Cold temperatures impact the conductance of stomata, carbon cycle, transpiration rate, and thylakoid electron transport.High temperatures are particularly detrimental to photosynthesis, as it disrupts the thylakoid membrane and inhibits enzymes and electrons, ultimately reducing the reaction rate.Although plants can adapt to high temperatures, extreme temperatures in the short term can disrupt chlorophyll biosynthesis.If exposed to extreme temperatures in the long term, chlorophyll degradation can result in irreversible damage [30].
The uptake of CO2 affected by catchment area size.A larger catchment area by plants increased the number of leaves and consequently improved the CO2 reduction.This illustrated the importance of considered such factors when assessed the reduction abilities of plants.However, higher elevations did not always produce the same effect.For instance, Epipremnum aureum showed a reduced ability to decrease CO2 at greater heights.Additionally, environmental factors such as temperature and sunlight influenced the reduction abilities of each plant.
This phenomenon was associated with the plant's ability to adapt to specific environmental conditions.The density and index of stomata, which were leaf structures that facilitated photosynthesis by enabling CO2 diffusion considerably affected by light intensity.Stomata opened widely in the morning due to favorable temperature and humidity and gradually closed as light and temperature increased.The stomatal apertures were most extensive during 09.00-10.00a.m.Nevertheless, high temperatures and light intensity brought about stomatal closure by noon [34].
Plants thrived in temperatures ranging from 10°C to 34°C but exhibited protective responses when exposed to temperatures outside this range.The temperature held significance in altered enzyme activities in leaves and initiated changes in plant growth phases.In high-temperature conditions, enzyme stability decreased, impaired photosynthesis II performance lowered electron transport rate, and decreased chlorophyll content.High temperatures increased membrane permeability, led to direct damage to the thylakoid membrane of the chloroplast.This hindrance resulted in decreased light harvesting, electron transport rate, and ATP production [34].
IOP Publishing doi:10.1088/1755-1315/1307/1/01200214 3.7.2.Internal Factors Photosynthesis.Numerous factors involved in reducing CO2 in each plant.In addition to external factors, several internal factors affected the rate of photosynthesis, such as the chlorophyll contents in the leaf, the accumulation of by-products, the protoplasmic factors, leaf anatomy, leaf age, and hormones.Glucose was produced as a by-product of photosynthesis, but its accumulation hindered the process.Therefore, ensured careful monitoring of photosynthetic by-products was crucial for achieving optimal photosynthesis.Various factors, included the thickness of the cuticles and epidermis, the size and distribution of intercellular spaces, the distribution of stomata, chlorenchyma development, and other tissues, affected photosynthesis in terms of leaf anatomy.Moreover, as a leaf matured, its photosynthetic rate typically increased until it reached complete development.However, as the leaf reached full expansion and ultimately underwent senescence, the deactivation of enzymes and degeneration of chlorophyll ensued.
Generally, smaller leaves were preferred in hot and dry environments while larger leaves with less efficient energy exchange capacity were suitable for cooler, humid, and low-radiation environments [35].This study showed that Antigonon leptopus and Vernonia elliptica plants had smaller leaves compared to Epipremnum aureum, which allowed them to thrived and reduced CO2 more effectively under high sunlight intensity environmental conditions.Each leaf has a maximum stomatal count per area determined by the size of the stomata.Stomata density and size varied between species, resulted in differences in substance exchange, water use, and photosynthetic rate.Greater transpiration occurred in plants with larger stomata compared to those with numerous smaller stomata.The growth of plants in high-light environments with fluctuated humidity resulting in faster response times led to the formation of smaller and more dynamic stomata.The density of stomata increased from the base of the tree to its top, indicated an adaptation to alterations in light conditions.[36].
Antigonon leptopus characterised by limited stomata to the underside of the leaf [38].Stomatal density ranged between 300 and 320, with a stomatal index of 17.13.In contrast, Epipremnum aureum had a stomatal density of 80.7 on the upper part of the leaf, with a stomatal index of 0.23.Additionally, the epidermis of this species displayed extensive distances, created sizeable gaps between the plant cell structures [38].The plant boasted a stomatal length of 44.35 µm, accompanied by a width of 21.18 µm [38].A greater stomatal density or stomatal index might result in a higher rate of photosynthetic induction [39].Consequently, Antigonon leptopus was more efficient in reduced CO2 compared to other plant species.

Linear and Polynomial Equations of CO2 Concentration
Each elevation and plant, with varying catchment areas, had differing plant uptake capabilities, which led to the creation of unique linear regression equations.Table 6 showed the connection between the function of x, represented the catchment area, and y which indicated the concentration of carbon dioxide (KCO2) in plants.The concentration of CO2 denoted as y, while x represented the area of plant cultivation, served as the independent variable for the function of y.The slope (for example -377.89) of the equation indicated the direction of the linear regression.A positive slope indicated a direct relationship, when the y value decreased, the x value also decreased.The equation produced negative results indicated an inverse relationship between y and x values.The area allocated for planting was represented by the x-axis, while the concentration of CO2 was represented on the y-axis.It is evident from the graph that the higher the concentration of CO2 reduction, the greater the planting or catchment area.Hence, the correlation between CO2 and planting area was not proportional.The application of this equation permitted the identification of plant species that are most efficient at absorbing CO2.For instance, by entering the x value as 100%, it was possible to determined which plants were most efficient at reducing CO2 in a specific catchment area.
The relationship between elevation and CO2 concentrations was displayed in table 7. The function x represented the plant's elevation, while y represented the carbon dioxide concentration (KCO2) within the plant.The equation for y represented the correlation with x in terms of elevation for planted species.Here, x denoted elevation and y signified the decline in CO2 concentration.CO2 concentration fluctuated at different elevations, so an increase in plant placement did not necessarily result in CO2 decrease.These variations occurred due to disparities in sunlight intensity and temperature.From this equation, it was possible to determined which plant absorbed the highest CO2 levels at the current elevation.

Correlation and Regression Analysis CO2 Concentration
The correlation test was a technique used to assess the potential of a linear relationship between two continuous variables in both directions.A negative coefficient indicated inverse proportionality and vice versa [40] The correlation test value compared to r value in the statistical table.If the calculated r value exceeded the r table, it indicated a mutual influence between the two variables.The regression analysis revealed the extent of the relationship or influence between the dependent and independent variables.This analysis comprised comparing the calculated t-value to the t-table value, which suggested a mutually significant association when the calculated t-value surpassed the t-table value.

Correlation and Regression Analysis in Each Plant
Reactor on the Variation of the Catchment Areas.Table 8 indicated that Epipremnum aureum and Vernonia elliptica did not affect each other or create a significant relationship when compared with the area catchment.This could be explained by the fact that decreased CO2 concentration in each area did not yield significant results and tended to move away from the regression line, rendering the results insignificant.Thus, it could be inferred that the plant area was not the sole reason for the decrease in CO2 concentration.The process of photosynthesis was affected by morphological factors in plants, such as the number of leaves and stems, stomata, and chloroplasts.The research suggested that an increase in the number of plants might lead to a reduction in the concentration of CO2.

Correlation and Regression Analysis in Each Plant
Reactor on the Variation of the Elevations.Table 9 revealed that only Epipremnum aureum had an impact on existing elevation levels, as not all plant species possessed this capability.The varied capacity of each plant species to absorb CO2 was the reason behind this phenomenon, and external conditions are among the contributing factors.Nonetheless, the presence of building shadows and canopies covering some reactors during certain conditions has impacted the sunlight intensity and the capacity of plants to assimilate and decrease CO2.As a result, there are confounding factors that researchers did not control, which have influenced the recorded CO2 concentration and consequently skewed the results.

Conclusions
The CO2 uptake values varied significantly among each plant.The morphology of each plant influenced the CO2 uptake ability, meaning a greater number of leaves and plants led to increased uptake.According to this study, Antigonon leptopus showed the highest CO2 uptake value at 314.18 ppm, while Epipremnum aureum and Vernonia elliptica displayed 126.04 ppm and 183.70 ppm respectively.Moreover, 75% of the catchment area in the reactor registered the highest CO2 uptake value.The study included elevation as a variable in the analysis of temperature, humidity, and sunlight intensity.The different results in CO2 concentration might be due to the elevated position of the reactor.Occasionally, certain reactors were covered by buildings and canopies, which changed the intensity of sunlight and hindered plant assimilation, ultimately has impacted the CO2 uptake capability.Consequently, there exist numerous confounding factors that were not controlled by researchers, which have a biased impact on the measurement of CO2 concentration.Therefore, it is crucial to understand the morphological traits of plants and the incoming sunlight levels.For instance, Antigonon leptopus and Vernonia elliptica, which have smaller leaf sizes, more leaves, and a higher stomatal density compared to Epipremnum aureum were capable of photosynthesis under high sunlight intensities efficiently.

Figure 1 .
Figure 1.Reactor illustration for each plant species.

Figure
Figure7showed that each reactor had different CO2 absorption abilities, which varied without following a set pattern.In the morning, the samples were similar to the control due to lower sunlight intensity, and photosynthesis inefficiency resulted.Residual CO2 generated by plant respiration during the night continued to be present and contributed to the CO2 concentration in the reactors.The CO2 concentration experienced a decrease from 07.00 a.m. until it once again surpassed the control CO2 concentration at 03.00 p.m.At 11.00 a.m., the concentration of CO2 in Antigonon leptopus with a catchment area of 75% reduced to 258 ppm at an elevation of 0 m.It decreased to 308 ppm at an elevation of 4.5 m and reached a minimum of 223 ppm at an elevation of 8.5 m.Plants were capable of efficiently reduced CO2 through photosynthesis during the daytime.At 11.00 a.m., a substantial amount of carbohydrates was founded in the leaves where photosynthesis occurred efficiently[28].Antigonon leptopus situated at an elevation of 4.5 m not experienced a significant decreased in CO2 concentration compared to other sites.This was due to limited exposure to sunlight, which shaded the plant species.Conversely, this significant decreased in CO2 concentration founded at an elevation of 8.5 m where there is sufficient exposure to sunlight.This indicated that this plant species thrives in areas with high levels of sunlight.After reached the point of saturation for daytime CO2 absorption, the plant's capacity to absorbed CO2 decreased, resulted in an elevation in the graph.At the point of peak light intensity, maximum CO2 saturation occurred.However, surplus energy absorbed from increased sunlight is not utilized efficiently, led to a decline in the efficiency of photosynthesis II.This, in turn, resulted in photoinhibition of photosynthesis[29].During the daytime, the CO2 concentration in the control was higher than that observed in the plant reactor.The vegetation could decrease CO2 concentration, however, plant respiration caused an increase in CO2 concentration during the late afternoon until nightfall, surpassed the control reactor.Insufficient sunlight reduced the activity of enzymes that are responsible for photosynthetic carbon assimilation.As a result, plant carbon assimilation was restricted, led to a decrease in photosystem II photochemistry's effective quantum yield[29].The planting of over 75% of the bed reactor area with plants resulted in a significant reduction in CO2 concentration.This observation implied a connection between the area of leaves, the amount of chlorophyll present, and the photosynthetic efficacy.The observation was supported by the point situated at the bottom of the curvilinear plot.The discoveries implied a plausible association between plant configuration and photosynthetic productivity.

Figure 10 .
Figure 10.CO2 uptake capacity of plants at various elevations and catchment areas.

Table 1 .
Number of plants required in each reactor.

Table 2 .
2, table 3, and table 4. CO2 concentration (ppm) per time in each reactor at 0 m elevation with the nearest point to the second-order polynomial regression line from figure 4.

Table 3 .
CO2 concentration (ppm) per time in each reactor at 4.5 m elevation with the nearest point to the second-order polynomial regression line from figure5.

Table 4 .
CO2 concentration (ppm) per time in each reactor at 8.5 m elevation with the nearest point to the second-order polynomial regression line from figure6.

Table 5 .
Results of KCO₂ value in each plant reactor.Internal and External Factors Affecting PhotosynthesisAntigonon leptopus founded more effective in reduced CO2 levels than Epipremnum aureum and Vernonia elliptica.Antigonon leptopus had a higher Air Pollution Tolerance Index (APTI) when 13compared with Epipremnum aureum and Vernonia elliptica

Table 6 .
Linear equation for KCO2 absorption by plant species (y) to catchment area (x).

Table 7 .
Polynomial equation for KCO2 absorption by plant species (y) to elevations (x).

Table 8 .
Correlation test of KCO2 values for each plant species and variation in catchment areas.

Table 9 .
Correlation test of KCO2 values for each plant species and variation in elevations.