Chennai: Vehicular pollution and indoor sources of pollution can increase pollution levels in homes and apartments with poor ventilation. But, a pilot study in the city has found that native indoor plants and common species can reduce common air pollutants to a limited extent. Researchers monitored two identical apartment balconies over one month, one with a curated mix of 17 plants and one without, using IoT-based sensors tracking carbon dioxide (CO2), carbon monoxide (CO), total volatile organic compounds (TVOCs), benzene, and formaldehyde. The planted balcony consistently recorded lower pollutant levels.During evening peak hours, CO2 levels were 984ppm in the non-planted balcony compared to 919 ppm in the planted space. Carbon monoxide dropped from 392 micrograms/cubic metre (m3) to 335 micrograms/m3, and TVOCs from 75 micrograms/m3 to 71 micrograms/m3. Absorption varied through the day. The highest CO2 reduction reached 161 ppm in the morning, while the lowest was 58 ppm at night. TVOC reduction ranged from one to 11 micrograms/m3, indicating a limited but measurable impact. Benzene levels returned to permissible limits within eight hours in the planted balcony, compared to about one and a half days without plants. Formaldehyde concentrations reduced within two hours after cleaning activities in the planted space, compared to three hours without plants. As per CPCB, the maximum permissible concentration (annual average) is 500 micrograms/m3 for VOC (volatile organic compounds), 50 micrograms/m3 for formaldehyde, 5 micrograms/m3 for benzene, 1000 micrograms/m3 for carbon dioxide, and 2000 micrograms/m3 for carbon monoxide.“Plants as a natural medium are inexpensive and best at absorbing air pollutants, thereby improving quality of the indoor environment,” said Swetha Madhusudanan, first author of the study. “The absorption by the plant palette is not uniform throughout the day and varies with environmental conditions and human activity.” The multi-institutional study, led by Dr M G R Educational and Research Institute, was published in Environmental Science and Pollution Research.The planting palette included areca palm, peace lily, Boston fern, tulsi, golden pothos, aloe vera, spider plant, and jade plant. These plants contributed to reducing CO2, CO, benzene, and VOCs, while aloe vera showed night-time CO2 uptake and spider and jade plants helped regulate indoor humidity. Researchers said Bougainvillea and vertical creepers help reduce heat gain by blocking incoming radiation at balcony openings.Indoor pollution levels were highest during peak traffic hours, particularly between 8-10 am and 6-8 pm, reflecting the influence of vehicular emissions. Activities such as floor cleaning and indoor painting temporarily increased formaldehyde and benzene levels.Researchers said while plants can act as passive filters at entry points such as balconies, their impact remains modest and they cannot replace mechanical ventilation or air filtration systems.
