The experimental observation, mechanism and kinetic studies on the reaction of hexachloro-1,3-butadiene initiated by typical atmospheric oxidants

Highlights: • The concentrations of HCBD in landfills and high altitude of mountain are more than in other observation places. • Hexachloro-1,3-butadiene initiated by typical atmospheric oxidants can lead to different mechanism. • The total rate constants of the Cl, NO₃,HO₂, OH and O₃ with HCBD at 298.15 K is 4.51 × 10⁻¹³ cm³ molecule⁻¹ s⁻¹. • The ratio of OH and Cl radicals with HCBD are more than those of NO₃, HO₂ and O₃. Hexachloro-1,3-butadiene (HCBD) is a persistent organic pollutant in the environment. When its samples were collected and observed, the levels of HCBD in its source and high mountains are higher than in urban cities, oil factories and countryside. The density functional theory is applied to the degradation mechanism of HCBD with Cl, NO₃, HO₂, OH and O₃. Those reactions are optimized and calculated at two carbon sites of double bonds, and then the subsequent reactions of the OH-initiated intermediates with O₂ and NO are taken as examples. Ozonization reactions of HCBD including the formation of primary and secondary ozonides are investigated. The Criegee intermediates created in the ozonization reactions can react with O₂, SO₂, NO₂ and H₂O. Reaction rate constants of the Cl, NO₃, HO₂, OH and O₃ initiated reactions with HCBD are calculated within 200 to 400 K with the transition state theory method, and the rate constants of the Cl, NO₃, HO₂, OH and O₃ at 298.15 K are 4.51 × 10⁻¹³, 1.32 × 10⁻²⁰, 4.33 × 10⁻²⁹, 6.33 × 10⁻¹⁶, 5.80 × 10⁻²⁷ cm³ molecule⁻¹ s⁻¹, respectively. The reactions of OH and Cl radicals with HCBD are more important than those of NO₃, HO₂ and O₃ according to the reaction rate branching ratio. Both the temperature and reaction rate could change with the height.