Social media big data reveals how mobility reshapes human environmental exposure inequality

• We compared residence-based and mobility-based measures of green exposure across 317 Chinese cities. • Residence-based measures significantly overestimate green exposure and its inequality. • When using mobility-based measures, the disparity between large and small cities decreases. • Differences in green exposure between high and low-income groups narrowed. • This is the first large-scale study incorporating human mobility data in green exposure assessment. For a long time, environmental exposure is considered closely related to people’s socioeconomic status (SES). Assessing this hypothesis seemed straightforward, as we could calculate the accessibility of green spaces around the residences of different socioeconomic groups, naturally concluding that high-SES residents enjoy higher green exposure. However, this assessment method relies on static residence-based evaluations without considering people’s daily mobility. In this study, we utilized over 100 million real activity locations and 1 million street view images to measure the mobility-based green exposure of approximately 20,000 users. We found that compared to the mobility-based green exposure, traditional residence-based assessments overestimate green exposure by 11.26% and green exposure inequality by as much as 54.44% (with the Gini coefficient decreasing from 0.5163 to 0.3343). The primary driver of changes in green exposure inequality is the reduction of within-group disparities. Further, after considering users’ mobility behavior, although high-income groups still experience higher levels and equality of green exposure compared to low-income groups, the relative gap in green exposure narrowed to 4.27%. This change is even more pronounced between cities, with the relative difference in green exposure between small and large cities shrinking from 32.70% to 16.83%. This study marks the first large-scale application of human mobility in environmental exposure research, significantly advancing our understanding of environmental exposure and inequality. The findings challenge long-standing conclusions in green exposure inequality studies, demonstrating that urban green exposure equity is higher than traditionally perceived. These results are also likely to be applicable to research on other similar environmental exposure issues.