Estimates of unintentional production and emission of hexachlorobutadiene from 1992 to 2016 in China.

Although hexachlorobutadiene (HCBD) has been listed as a persistent organic pollutant (POP) under Annexes A and C of the Stockholm Convention, information about its unintentional production and emission is still very limited. We estimated the historical unintentional production and emission of HCBD during 1992-2016 in China based on aggregated activity data and emission functions. The unintentional production of HCBD increased from 60.8 (95% confidence interval, 38.2-88.5) MT/yr to 2871.5 (2234.2-3530.0) MT/yr during 1992-2016, representing an average annual growth rate of 17.4%. The main unintentional source of HCBD changed from carbon tetrachloride to trichloroethylene production during this period. We estimated that China's cumulative emissions of HCBD were 8211.3 (6131.5-10,579.5) MT during the same period. HCBD consumption and the chlorinated hydrocarbon production sector were the major contributors to total HCBD emissions. Owing to the long-range transport capability of HCBD (8784 km), such high emissions in China may cause adverse effects in other regions.