Air pollution induced vegetation stress - The Air Pollution Tolerance Index as a quick tool for city health evaluation

Air Pollution Tolerance Index (APTI) is used to assess how tolerant plant species are of air pollution; it also serves to identify tolerant plant species that can be useful for pollution removal. APTI is calculated from parameters that are affected by air pollutants, such as ascorbic acid content, total chlorophyll content, relative water content and pH of leaf extract. In this study we report APTI values of two common tree species (Celtis occidentalis and Tilia sp.) in Debrecen, Hungary. We also ran a meta-analysis to compare APTI values among various global cities and land use types (industrial, roadside and urban) using robust ANOVA. APTI's relationship with city population and PM10 (particulate matter with aerodynamic diameter smaller than 10 mu m) was analysed using regression modelling and Principal Component Analysis. We applied Random Forest Regression for statistical model building. We demonstrated that the tolerance of tree species is higher in industrial areas and in cities with high pollution levels than in control areas. We found a strong positive correlation between APTI and the size of cities. The cities showed a separation along the first principal component, which was also correlated with APTI and the size of cities. Our results show that APTI is an efficient tool in air pollution monitoring and in decision making during urban development and urban greening.