Technical specifications of urban forests for air purification: A case study in Tokyo, Japan

Abstract

Air pollutants removed by urban forests were calculated for 53 municipalities in Tokyo, Japan based on remotely sensed imagery of urban forest within each municipality as well as local air quality and weather data in 2016. Annual air pollutant removal for Tokyo was 961 tons/year (ranging from 408 to 1,786 tons/year), of which 52.9% was contributed by the urban area (special wards), while 47.1% was by the suburban/rural area (Tama municipalities). Spatial tendencies of the air pollutant removal were analyzed based on the comparisons between the annual results for the special wards and the Tama area. Temporal tendencies were also analyzed based on the comparisons among the monthly results. Based on the results, technical specifications of urban forests in terms of removing air pollutants were quantified annually and monthly in the municipalities. They are represented as pollutants’ mass removed per unit tree cover area (i.e., g/m2) per year or month. These technical specifications enable to provide quick and easy quantitative evaluations of urban forests of any size anywhere in Tokyo. They in turn allows the municipalities' green master plans to better address the functions and values of urban forests in more objective and quantitative ways, which may lead to a mutual understanding of its values between government officials and citizens.