Sensitivity study of plant species due to traffic emitted air pollutants (NO2 and PM2.5) during different seasons in Dhaka, Bangladesh

Abstract

The impact of traffic emitted nitrogen dioxide (NO2) and fine particulate matter (PM2.5) on various plant species (Polyalthia longifolia, Swietenia mahagoni, Artocarpus heterophyllus) during different seasons (summer, rainy, and winter) was studied in greater Dhaka city (traffic, residential, and control site), Bangladesh. Air pollution tolerance index (APTI) of these plant species was determined from the measured concentrations of total chlorophyll content (TCC), ascorbic acid (AAC), relative water content (RWC), and pH of the leaf extract. TCC and AAC concentrations in leaves species were determined with UV–visible spectrophotometer. NO2 concentration was determined with Aeroquel (New Zealand), and PM2.5 was determined with Aerocet (USA). The measured NO2 and PM2.5 concentrations at each sampling location were used to establish a relationship with the determined APTI values. The average value of TCC, AAC, and RWC was found much lower in traffic site compared than that of the control site. High pollution stress on plants was also found in traffic sites showing 30% lower APTI values. The plants become sensitive if the APTI value is smaller than or equal to 12 (APTI ≤ 12). However, the average APTI values in different seasons showed a significant variations and followed the sequence—rainy season (8.10) > summer (7.34) > winter (6.69). The plants had the highest sensitivity towards pollutants during winter time. The average APTI values also varied depending on the locations and plant species with a total average of 7.38 ± 1.17, which indicates the sensitivity of plants towards pollution. On average, the measured concentration of NO2 was 223 ± 0.15 μg m−3 and PM2.5 mass was 125.7 ± 0.05 μg m−3. The APTI values showed a strong negative correlation with traffic emitted pollutants NO2 (R2 = 0.86) and PM2.5 (R2 = 0.70) indicating threats towards the plants survival.