Emission and risk of atmospheric hexachlorobutadiene might be underestimated globally.

Ambiguous emission of new pollutants is a fundamental obstacle of risk prevention, such as hexachlorobutadiene (HCBD). To quantify the HCBD emission in China, we probed the emission factors for main sources based on analysis of 847 gas samples from field experiments. Considering treatment efficiency, emissions of 362 kinds of sources were measured. Results showed that 15115.34 tons HCBD were emitted in 2019, among which more than half was contributed by agricultural sources (53.85 %) that were overlooked in ongoing HCBD regulation. More industrial sectors were recognized to produce and emit HCBD with the cumulative contribution being 29.35 %, such as industrial coating, plastic and rubber products manufacturing industry. Residential coal and transportation contributed 11.03 % and 5.5 % to total HCBD emission. Significant occupational health threats in the chemical raw material manufacturing industry indicated that low emission did not mean low risk, since emission of this industry was low. Assessment of population-weighted non-occupational risk revealed a higher risk for residents in Central and Eastern China. High detection rate of HCBD in agricultural and industrial sources implied a probably underestimated emission and impact over the globe. The conclusions highlight the importance of emission factor localization and source full-coverage in new pollutants regulation.