A Comparative Assessment of Elemental Concentrations in Combustibles of Urban Landscape Tree Species, Tree Organs, and Their Concentration in PM2.5 Emitted During Combustion

The emissions of PM2.5 from biomass combustion pose significant health risks due to their small size and chemical composition, which can lead to various diseases. Understanding the relationship between PM2.5 elemental concentrations and biomass elemental concentrations is essential. This study analyzed the concentrations of four key elements—sodium, calcium, potassium, and phosphorus—in the combustibles of two urban landscape tree species (conifers and broad-leaf) and their respective tree organs (branches and leaves), along with the PM2.5 generated during combustion. Using R and Origin 2024 Pro software, respectively, the concentration of elements and the strength and direction of elemental relationships were assessed among tree species categories, tree organs, and in PM2.5 emitted. Calcium was highly concentrated in both tree species, followed by potassium, which had higher concentrations in broad-leaf species. Elemental concentrations also differed significantly between branches and leaves, with calcium consistently being the most concentrated in both. While calcium and potassium levels were high in combustibles, they were relatively low in PM2.5 compared to other elements. The study revealed stronger correlations among elements in PM2.5 as compared to relationships between elements in combustibles and their counterparts in PM2.5. Sodium with a lower concentration in the combustibles was readily released as compared to other elements (K, P, and Ca), which were highly concentrated in the combustibles but not readily released in PM2.5. These variations highlighted the importance of considering tree species, organ types, and elemental interactions when assessing the impacts of biomass combustion on urban air quality.