A five-year long homogenized daily in situ PM2.5 concentration dataset was generated on the basis of discrete data records retrieved from the China National Environmental Monitoring Center (CNEMC) via a web crawler during 2015-2019. A set of methods for the purposes of gap filling, data merging, homogeneity test, and bias correction were geared up seamlessly to improve the data integrity and to make essential adjustments to the inherent discontinuities detected in each PM2.5 concentration record. After essential quality control, a dataset including 1,309 long-term coherent yet temporally complete PM2.5 concentration time series at a daily resolution between 2015 and 2019 was carefully compiled
