Removal of Particulate Matter from Ambient Air by Four Evergreen Tree Species in Dhaka, Bangladesh

Abstract

BACKGROUND AND AIM: An investigation was conducted to assess the particulate matter (PM) removal capacity of four common roadside trees (Ficus benghalensis, Ficus religiosa, Mangifera indica, and Polyalthia longifolia) grown at four locations in Dhaka, Bangladesh. METHODS: Gravimetric analyses were performed separately to quantify PM in three size fractions (0.2-2.5 µm, 2.5-10 µm, and 10-100 µm) deposited on surfaces and trapped in waxes. The particulate matter deposited on the leaves of the studied plants was also analyzed for cadmium (Cd), chromium (Cr), lead (Pb), and nickel (Ni) concentrations. RESULTS:Among the species studied, the deposited mass of PM was highest on Ficus benghalensis. The mean PM load on plant foliage was significantly greater in the polluted sites compared with the control site (p0.05). Most of the PM accumulated on plant foliage belonged to the large fraction size (10-100 µm). Species-wise significant differences were also found among the sites with respect to total PM, surface PM, and wax-embedded PM (p0.05). The amount of wax deposited on the leaves of plants grown in these sites also differed (p0.05). A positive correlation was found between wax-embedded PM of diameter 0.2-2.5 µm and the amount of waxes. Ficus benghalensis was found to be the most effective with respect to total PM accumulation. On the other hand, Mangifera indica was found to be the most effective accumulator of wax-related PM and seems to be the best species for traffic-related sites, where organic substances from vehicle exhausts are present in high concentrations. CONCLUSIONS:PM concentration was found to be significantly correlated to the concentrations of Cd and Pb meaning these two trace elements deposited simultaneously with the PM and originated from common anthropogenic sources. Total metal accumulation capacities of different plants were evaluated using the metal accumulation index (MAI) and Ficus benghalensis was found to have the highest MAI value (13.60). KEYWORDS: particulate matter, roadside species, trace element, metal accumulation index