Decreased gaseous carbonyls in the North China plain from 2004 to 2017 and future control measures

Gaseous carbonyls are important precursors of ozone and secondary organic aerosols. To study the characteristics of small-molecule carbonyls (SMC), samples were collected with 2, 4-dinitrophenylhydrazine in Xianghe at the junction of the Beijing, Tianjin and Hebei regions from November 2017 to January 2018 and were subjected to high-performance liquid chromatography-ultraviolet analysis. The mean concentration of SMC was 4.5 +/- 1.1 ppbv, and the observed compounds included acetone (1.9 +/- 1.3 ppbv), acetaldehyde (1.3 +/- 1.0 ppbv) and formaldehyde (1.2 +/- 0.9 ppbv). Compared with the observations in the Beijing-Tianjin-Hebei region from 2004 to 2017, the concentration of SMC decreased and the trends were -1.13, -0.44 and -0.45 ppbv yr(-1), respectively. Using volatile organic compounds as tracers, positive matrix factorization was used to analyze the sources of the SMC. The results showed that, in addition to secondary and long-lived species (84.8%), the main sources of SMC in Xianghe were vehicle emission (8.5%), solvent usage (3.7%) and coal and biomass combustion (3.0%). The significant decline in the contributions of vehicle emissions, coal and biomass combustion is the main reason for the decline in the SMC concentrations. Based on fine particulate matter concentrations, this study found that with the deterioration in air quality, the contribution of each source changed insignificantly. Although the concentrations of SMC dropped significantly, vehicular sources remained the most important sources in this region.