Abstract
<jats:p>Global atmospheric contamination with hexachlorobuta-1,3-diene (HCBD) has been rising rapidly for the past decade, despite its listing as a persistent organic pollutant (POP) under the Stockholm Convention. The unintentional nature of its production makes it challenging to identify emission sources. A multi-pronged investigation integrating monitoring evidence, emission estimation, and environmental transport modeling reveals that Chinese emissions, likely from chlorinated solvent manufacturing, are necessary and sufficient to explain the temporal and spatial trends in HCBD contamination recorded in East Asia and across the globe. A multiple-fold increase of emissions after the time of listing underscores significant shortcomings in the provisions of Article 5 of the Convention in reducing, let alone eliminating, the environmental releases of unintentionally produced POPs.</jats:p>