A homogenized daily in situ PM _2.5 concentration dataset from the national air quality monitoring network in China

In situ PMinline-formula_2.5 concentration observations have long been used as critical data sources in haze-related studies. Due to the frequently occurring haze pollution events, China started to regularly monitor PMinline-formula_2.5 concentration nationwide from the newly established air quality monitoring network in 2013. Nevertheless, the acquisition of these invaluable air quality samples is challenging given the absence of a publicly available data download interface. In this study, we provided a homogenized in situ PMinline-formula_2.5 concentration dataset that was created on the basis of hourly PMinline-formula_2.5 data retrieved from the China National Environmental Monitoring Center (CNEMC) via a web crawler between 2015 and 2019. Methods involving missing value imputation, change point detection, and bias adjustment were applied sequentially to deal with data gaps and inhomogeneities in raw PMinline-formula_2.5 observations. After excluding records with limited samples, a homogenized PMinline-formula_2.5 concentration dataset comprising of 1309 5-year long PMinline-formula_2.5 data series at a daily resolution was eventually compiled. This is the first attempt to homogenize in situ PMinline-formula_2.5 observations in China. The trend estimations derived from the homogenized dataset indicate a spatially homogeneous decreasing tendency of PMinline-formula_2.5 across China at a mean rate of about inline-formula−7.6 % per year from 2015 to 2019. In contrast to raw PMinline-formula_2.5 observations, the homogenized data record not only has complete data integrity but is more consistent over space and time. This homogenized daily in situ PMinline-formula_2.5 concentration dataset is publicly accessible at https://doi.org/10.1594/PANGAEA.917557https://doi.org/10.1594/PANGAEA.917557 (Bai et al., 2020a) and can be applied as a promising dataset for PMinline-formula_2.5-related studies such as satellite-based PMinline-formula_2.5 mapping, human exposure risk assessment, and air quality management.