Urban green vitalization and its impact on green exposure equity: A case study of Shanghai city, China

Urban green space (UGS) provides multiple ecosystem services to enhance the residents' well-being in the cities. As a characterization of differences in the degree of interaction between residents and UGS, Green exposure equity, has been recognized as an environmental justice issue. In this study, we propose the concept of urban green space' vitalization (UGV) as a primary criterion for assessing whether the UGS' functions or services are realized. Taking Shanghai, China as a case study, we developed an assessment system for UGV, and quantified UGV's availability to examine the impact on green exposure equity. Our research shows that 1000 m is the optimal service radius to determine whether UGS vitality is realized. All UGS in the central regions of Shanghai have realized their vitality, while areas devoid of vitality are mainly located in the non-central. Compared to UGS, the availability of UGV in Shanghai was cumulatively reduced by 321.07 km², 10,812.61 km², and 197,496.54 km² for walking, public transport, and driving modes, respectively. In the non-central regions, the minimum green availability per capita for walking and public transport modes was reduced to 0 ha. The influence of UGV on green exposure equity varies depending on research scales and travel modes, as it is affected by heterogeneity in the distribution of UGS and population. Our research confirmed that UGV significantly reduces green availability and influences green exposure equity. Green exposure equity could be significantly improved by UGV under public transport mode and the district scale. Therefore, UGV is an essential factor in quantifying the equity of green exposure. Our research can serve as a basis for more realistic measurements of green exposure equity, providing insights for improving environmental justice in sustainable cities.