E-Commerce Growth Reduces Primary PM_2.5 Emissions but Increases Secondary PM_2.5 Precursors in China

The rapid shift from traditional in-store to online shopping has raised critical questions about its environmental trade-offs, particularly regarding air pollution─a key contributor to public health risks and climate change. Despite growing concerns, incomplete assessments have hindered the development of effective emission mitigation strategies for the retail sector. In this study, we compiled a comprehensive air pollutant emission inventory for shopping activities in China from 1990 to 2023, comparing in-store and online shopping methods. Our analysis reveals that online shopping reduces PM_2.5 emissions from the retail sector by 19% (0.013 g item^-1 vs 0.031 g item^-1), primarily due to the greater efficiency of courier deliveries compared to consumer travel to stores. However, emissions of secondary PM_2.5 precursors (NO_x, SO₂, NMVOCs) increase substantially─by 49, 270, and 30%, respectively─driven by air freight use and overpackaging. Targeted strategies, such as shifting from consumer vehicles to walk and cycling, replacing air freight with high-speed railway freight, and adopting reusable packaging, could mitigate these impacts. Implementing these measures is essential for advancing sustainable retail practices amid the growth of E-commerce.