Nitrate sources and its formation in precipitation during typhoons (In-fa and Chanthu) in multiple cities, East China

A clear understanding of the factors governing dual isotopes (delta N-15-NO3- and delta O-18-NO3-) in typhoons is essential for understanding their NO3- sources and its formation mechanisms. In this study, sequential precipitation samples during typhoons, including In-fa and Chanthu, were collected from Ningbo, Hangzhou and Huzhou. The chemical compositions, nitrogen and oxygen isotopes of NO3- and oxygen isotopes of H2O (delta O-18-H2O) were measured. The results showed that the delta N-15-NO3- and delta O-18-NO3- values ranged from -6.3 parts per thousand to 6.0 parts per thousand, and 38.0 parts per thousand to 66.5 parts per thousand, respectively. The lower delta O-18-NO3- values (less than 52 parts per thousand) indicated the importance of peroxy radicals (RO2 or HO2) in NOx oxidation to NO3- formation pathways. By the Monte Carlo simulation of delta O-18-NO3- values of typhoons, the calculated oxidation proportions of NO by RO2 (or HO2) during the OH center dot pathway ranged from 0% to 27% of In-la and from 0% to 32% of Chanthu, respectively, in the three cities. More NO, emissions from marine microbial processes caused the lower delta N-15-NO values of typhoons in Ningbo than those in Hangzhou and Huzhou. The variation in delta N-15-NO3- values in sequential samples in In-fa reflected the decreased marine sources (lightning) and the increased anthropogenic sources in land (coal combustion and microbial N cycle) from Phrase 1 to Phrase II and III. Based on the improved Bayesian model with nitrogen isotopic fractionation, the contributions of lightning + biomass burning, coal combustion, mobile sources and the microbial N cycle were 35.7%, 22.5%, 27.1% and 14.7% in In-fa, and 28.3%, 32.3%, 28.0% and 11.4% in Chanthu, respectively, in the three cities, emphasizing the influence of marine NO, sources (lightning). The results highlight the importance of RO2 (or HO2) in NOx oxidation pathways in typhoons and provide valuable insight into the NO(x )sources of typhoons.

Automated summary

Understanding the factors governing dual isotopes in typhoons is crucial for understanding their NO3- sources and formation mechanisms. This study collected precipitation samples during typhoons and measured the chemical compositions, nitrogen and oxygen isotopes of NO3- and oxygen isotopes of H2O. The results showed the importance of peroxy radicals in NOx oxidation pathways and the influence of marine NOx sources. The Bayesian model demonstrated the contributions of different sources in typhoon NOx. This research provides valuable insights into the NOx sources of typhoons and highlights the importance of RO2 (or HO2) in oxidation pathways.