Role of Urban Trees in Minimizing the Atmospheric Carbon Dioxide Level of the Megacity of Kolkata, India

The megacity of Kolkata (22°33′36.00″N and 88°25′12.00″ E) in the maritime state of West Bengal (India), with a population of some 15 million and population density of about 24,000 individuals per square km, is noted for its high population density, large number of vehicles and several industrial units at the outskirt of the city. However, due to unplanned urban expansion at the cost of trees and wetlands areas in the city, the use of low-grade fuel to run the vehicles, and emissions from industrial units (mostly without proper treatment), the near-surface atmospheric carbon dioxide level has hiked up and crossed the threshold value. In this study, we assessed the level of atmospheric CO2 in five major locations of the city for more than three decades (1990–2022) through three seasons (premonsoon, monsoon, and post-monsoon). The near-surface atmospheric CO2 level showed the highest value of 427 ppm (during March 2019 at Moulali; Stn. 1) and the lowest value of 326 ppm (during September 2020 at Park Circus; Stn. 5). The stored carbon in the Above Ground Stem Biomass (AGSB) referred to as Above Ground Stem Carbon (AGSC) of the dominant tree species and common to all these sites was estimated during March 2022 to identify the species-wise carbon storage potential of the planted trees. The mean values of AGSC exhibit the order Azadirachta indica > Tamarindus indica > Aegle marmelos > Delonix regia > Mangifera indica > Ficus religiosa > Acacia auriculiformis > Cocos nucifera > Bombax ceiba > Tectona grandis > Terminalia arjuna > Albizia saman > Ziziphus mauritiana > Artocarpus heterophyllus > Alstonia scholaris in all the selected sites. The present study highlights the potential of urban trees to store carbon within the stem biomass, which may serve as a practical roadmap to combat the rising trend of carbon dioxide in the near-surface atmosphere of the city.