A diurnal story of Δ17O($$\rm{NO}_{3}^{-}$$) in urban Nanjing and its implication for nitrate aerosol formation

Abstract

Inorganic nitrate production is critical in atmospheric chemistry that reflects the oxidation capacity and the acidity of the atmosphere. Here we use the oxygen anomaly of nitrate (Δ17O($$\rm{NO}_{3}^{-}$$ NO 3 − )) in high-time-resolved (3 h) aerosols to explore the chemical mechanisms of nitrate evolution in fine particles during the winter in Nanjing, a megacity of China. The continuous Δ17O($$\rm{NO}_{3}^{-}$$ NO 3 − ) observation suggested the dominance of nocturnal chemistry (NO3 + HC/H2O and N2O5 + H2O/Cl−) in nitrate formation in the wintertime. Significant diurnal variations of nitrate formation pathways were found. The contribution of nocturnal chemistry increased at night and peaked (72%) at midnight. Particularly, nocturnal pathways became more important for the formation of nitrate in the process of air pollution aggravation. In contrast, the contribution of daytime chemistry (NO2 + OH/H2O) increased with the sunrise and showed a highest fraction (48%) around noon. The hydrolysis of N2O5 on particle surfaces played an important role in the daytime nitrate production on haze days. In addition, the reaction of NO2 with OH radicals was found to dominate the nitrate production after nitrate chemistry was reset by the precipitation events. These results suggest the importance of high-time-resolved observations of Δ17O($$\rm{NO}_{3}^{-}$$ NO 3 − ) for exploring dynamic variations in reactive nitrogen chemistry.

Formation Mechanisms and Source Apportionments of Nitrate Aerosols in a Megacity of Eastern China Based On Multiple Isotope Observations

“…This phenomenon revealed the enhanced photochemical capabilities of atmosphere and the less importance of heterogeneous reactions in the fresh nitrate production when the air pollutants were cleaned by the rain, which was supported by the previous study of oxygen isotopes of nitrate in precipitation (Y.‐L. Zhang et al., 2022).…”

“…Meanwhile, O 3 increased to 20.7 ppb and the ALWC was extremely low (4.9 μg m −3 ; Figure 1d and Figure S5 in Supporting Information S1). This phenomenon revealed the enhanced photochemical capabilities of atmosphere and the less importance of heterogeneous reactions in the fresh nitrate production when the air pollutants were cleaned by the rain, which was supported by the previous study of oxygen isotopes of nitrate in precipitation (Y.-L. Zhang et al, 2022). In summer, the high values of Δ 17 O-NO 3 − (>30‰) were found on 17 and 24 August (Figure 1b), indicating the high contribution of NO 2 + HC/H 2 O pathway.…”

Vertical Differences of Nitrate Sources in Urban Boundary Layer Based on Tower Measurements

“…Over the years, numerous studies around the world have observed δ 15 N of p NO 3 – and used the data set to identify the emission sources of atmospheric NO x in different regions. − However, even in the most densely sampled region like Beijing, δ 15 N­(NO 3 – ) records still remain spatially fragmented. This makes it difficult to understand the vertical distribution of nitrate sources from the ground surface to high altitudes, as nitrate aerosols are influenced by emissions, meteorology, and transport.…”

Chemical Compositions, Sources, and Intra‐Regional Transportation of Submicron Particles Between North China Plain and Twain‐Hu Basin of Central China in Winter

“…With the weakening of gas‐particle distribution, the main formation mechanism of NO 3 − in winter daytime was the photochemical formation (NO 2 + OH/H 2 O), the contribution of which showed the highest increase around noon with 48% (Sun et al., 2013; Zhang et al., 2022). While the nocturnal chemistry (NO 3 + HC/H 2 O and N 2 O 5 + H 2 O/Cl − ) in the haze night suggested the dominance and the contribution peaked at midnight with an increase even of 72% (Zhang et al., 2022). In contrast, the high level of sulfate (7.4 ± 3.8 μg m −3 ; from 2.2 to 20.3 μg m −3 ) in winter was mainly observed during severe haze events with high humidity (85.1%–97.3%) (Figure S11 in Supporting Information ).…”

“…The ambient temperature in this study fluctuated between −5°C and 5°C and was relatively constant between different RH values, which made the NO 3 − be readily concentrated in the particle phase. With the weakening of gas‐particle distribution, the main formation mechanism of NO 3 − in winter daytime was the photochemical formation (NO 2 + OH/H 2 O), the contribution of which showed the highest increase around noon with 48% (Sun et al., 2013; Zhang et al., 2022). While the nocturnal chemistry (NO 3 + HC/H 2 O and N 2 O 5 + H 2 O/Cl − ) in the haze night suggested the dominance and the contribution peaked at midnight with an increase even of 72% (Zhang et al., 2022).…”