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 mu g m(-3). The delta N-15-NO3- ranged from -1.58 parts per thousand to +8.74 parts per thousand, with an average of +2.79 parts per thousand +/- 3.32 parts per thousand. Influenced by the explosion, delta N-15-NO3- decreased significantly, which was in accordance with the industrial processes of explosives. The delta O-18-NO3- varied between +49.40 parts per thousand and +69.52 parts per thousand, and showed a marked increase (+66.62 parts per thousand +/- 3.92 parts per thousand) in the explosion-affected period. Using Monte Carlo simulation, the center dot 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 mu mol 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 mu mol N m(-2) d(-1)), the total nitrogen deposition increased by 308.49 mu mol 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 x 10(4) km(2), which is about 20% of the total area.