Impact of an accidental explosion in Tianjin Port on enhanced atmospheric nitrogen deposition over the Bohai Sea inferred from aerosol nitrate dual isotopes

In recent years, emergent pollutant’s accidents have occurred frequently in China, causing serious harm to the ecological environment. In this study, the impact of an accidental fire and explosion at Tianjin Port in 2015 on the atmosphere over the Bohai Sea was explored. Results showed sharp increases in the concentrations of several important components of fine particulate matter (e.g. NO₃⁻, SO₄²⁻, NH₄⁺, organic carbon, elemental carbon) over Beihuangcheng Island after the explosion. Among them, NO₃⁻ was most affected (about 10 days), with a maximum concentration of 16.45 μg m⁻³. The δ¹⁵N-NO₃⁻ ranged from −1.58‰ to +8.74‰, with an average of +2.79‰ ± 3.32‰. Influenced by the explosion, δ¹⁵N-NO₃⁻ decreased significantly, which was in accordance with the industrial processes of explosives. The δ¹⁸O-NO₃⁻ varied between +49.40‰ and +69.52‰, and showed a marked increase (+66.62‰ ± 3.92‰) in the explosion-affected period. Using Monte Carlo simulation, the •OH pathway for NO₃⁻ formation was 51.79% ± 10.94% at that time — much lower than in the regular period. The elevated dry deposition of NO₃⁻ caused by the explosion was 266.08 μmol N m⁻² d⁻¹ over the Bohai Sea — again, much higher than in the regular period. With the dry nitrogen deposition of NH₄⁺ (42.41 μmol N m⁻² d⁻¹), the total nitrogen deposition increased by 308.49 μmol N m⁻² d⁻¹, leading to severe ecological risk. Through the inverse computation of the dry deposition flux of NO₃⁻, the affected area over the Bohai Sea was less than 1.42 × 10⁴ km², which is about 20% of the total area.