Continental Emissions Influence the Sources and Formation Mechanisms of Marine Nitrate Aerosols in Spring Over the Bohai Sea and Yellow Sea Inferred From Stable Isotopes

The influence of continental emissions on the origin and formation mechanisms of atmospheric particulate nitrate (rho-NO3-) aerosols in the marine boundary layer remains unclear. Here, synchronous observations of nitrogen isotope ratios (delta 15N-NO3-) and oxygen isotope anomaly (Delta 17O-NO3-) in rho-NO3- were conducted across the Yellow Sea and Bohai Sea in Eastern China. Nitrate concentrations, delta 15N-NO3- and Delta 17O-NO3- exhibited a pronounced north-to-south latitudinal gradient. Combined with backward air mass trajectory analysis, the high nitrate concentration and isotopic characteristics in the northern sea area were found to be affected by the continental outflow near China while the low values in the southern sea area were more related to the oceanic inflow. Stable isotope analysis in R (SIAR) indicated that near the northern sea area, the nitrate radicals (NO3) reacted with hydrocarbons (HC) or dimethyl sulfides (DMS) pathway (NO3 + HC/DMS) played a leading role in nitrate production, whereas the NO2 + OH pathway dominated near the southern sea area. Nitrate in the northern seas originated mainly from nitrogen oxides (NOx = NO + NO2, the gaseous precursor of nitrate) emitted from continental sources, especially coal combustion and biomass burning. While closer to the southern seas, the proportion of NOx generated in the marine environment (from ship and biogenic emissions) increased. Overall, the differential relative contributions of continental and marine atmospheric chemistry and NOx sources lead to the spatial distribution characteristics of atmospheric nitrate concentrations and isotopic values over the Yellow and Bohai Seas. This study investigated the impact of emissions from land sources on the formation of nitrate particles in the air above the marine boundary layer. The researchers conducted observations of nitrogen and oxygen isotopes in nitrate particles across the Yellow Sea and Bohai Sea in Eastern China. They found that nitrate concentrations and isotopic ratios showed a clear gradient from north to south. By analyzing the trajectory of air masses, they determined that high nitrate concentrations in the northern sea area were influenced by emissions from the nearby continent, while lower values in the southern sea area were more related to the ocean. The analysis also revealed that different chemical pathways were responsible for nitrate production in these regions. In the northern seas, nitrate production was primarily driven by the reaction of nitrate radicals with hydrocarbons or dimethyl sulfides, while in the southern seas, the dominant pathway involved the reaction of nitrogen dioxide with hydroxyl radicals. The study further showed that nitrate in the northern seas mainly originated from nitrogen oxides emitted by continental sources such as coal combustion and biomass burning, whereas closer to the southern seas, a larger proportion of nitrogen oxides were generated within the marine environment. Continental outflow significantly affects the sources and formation mechanisms of atmospheric nitrate in nearshore marine areas As continental outflow diminishes, local chemistry and marine-generated NOx become pivotal in producing atmospheric NO3- in the open ocean. In polluted marine boundary layers, NO3 radical-related chemistry may play a significant role in the formation of nitrate