Seasonal variations in the amount of black carbon particles deposited on the leaf surfaces of nine Japanese urban greening tree species and their related factors.

As black carbon (BC) particles can be deposited on the leaf surfaces, urban greening is considered to be effective in purifying urban air. However, little information on the seasonal variations in the amount of BC particles deposited on the leaf surfaces (BC amount on the leaves) is available in Japanese urban greening tree species. Therefore, we investigated seasonal variations in the BC amount on the leaves of evergreen (, , and ) and deciduous (, , , and ) broad-leaved tree species. The BC amount on the leaves tended to increase from April for different periods, and then reached a saturated state in the tree species, excluding . In the 4 evergreen broad-leaved trees, the seasonal variation was positively correlated with the atmospheric concentration of BC particle. In the 5 deciduous broad-leaved trees, the seasonal variation was negatively and positively correlated with the water-repellence (water droplet contact angle) and the amount of epicuticular wax on the leaf surface, respectively. Therefore, the BC amounts on the leaves of evergreen and deciduous broad-leaved urban tree species are considered to be mainly regulated by environmental factors and leaf surface characteristics, respectively.