Long-term Trends in PM2.5 Chemical Composition and Its Impact on Aerosol Properties: Field Observations from 2007 to 2020 in Pearl River Delta, South China - He, Y.; Ding, X.; He, Q.; Zhang, Y.; Chen, D.; Zhang, T.; Yang, K.; Wang, J.; Cheng, Q.; Jiang, H.; Wang, Z.; Liu, P.; et al. (Atmos. Chem. Phys., 2025)