Nitrate (NO3−), which is mainly oxidized from NO2 by the OH radical (OH·) and O3 in the atmosphere, is a major component of inorganic aerosols. However, the contributions of the OH· and O3 pathways to NO3− in urban aerosols and the influence of air pollution to both pathways remain unclear. Oxygen isotopes of NO3− were measured for PM2.5 in Beijing in 2014. The Δ17O‐NO3− values (17.0–32.8‰) were significantly higher in winter (27.2 ± 3.6‰) than in summer (24.2 ± 1.3‰). By estimating contributions of O3 to the NOx cycle, the Δ17O values of NO3− endmembers produced via the NO2 + OH· (P1), NO3· + DMS/HC (P2), and N2O5 hydrolysis (P3) pathways were calculated for each observation. The contributions of the three pathways (P1: 32 ± 10%, P2: 34 ± 10%, and P3: 34 ± 20% annually) were calculated using the Stable Isotope Analysis in R model. We found that NO3− formation was dominated by the O3 oxidation pathways (P2 + P3; 68 ± 23% annually, 73 ± 21% in spring, 59 ± 23% in summer, 75 ± 20% in autumn, and 69 ± 22% in winter). Moreover, PM2.5, NO2, and NO3− pollution decreased the importance of the OH· pathway relative to the O3 pathways for NO3− production. However, O3 pollution increased the importance of the OH· pathway relative to the O3 pathways for NO3− production. These results provided a comprehensive analysis on the oxygen isotope records in particulate NO3− for understanding the relative importance of major oxidation pathways of NO2. Atmospheric pollution substantially influenced the pathways of NO2 oxidation to NO3− in city environments.

Although we know that rainfall interception (the rain caught, stored, and evaporated from aboveground vegetative surfaces and ground litter) is affected by rain and throughfall drop size, what was unknown until now is the relative proportion of each throughfall type (free throughfall, splash throughfall, canopy drip) beneath coniferous and broadleaved trees. Based on a multinational data set of >120 million throughfall drops, we found that the type, number, and volume of throughfall drops are different between coniferous and broadleaved tree species, leaf states, and timing within rain events. Compared with leafed broadleaved trees, conifers had a lower percentage of canopy drip (51% vs. 69% with respect to total throughfall volume) and slightly smaller diameter splash throughfall and canopy drip. Canopy drip from leafless broadleaved trees consisted of fewer and smaller diameter drops (D50_DR, 50th cumulative drop volume percentile for canopy drip, of 2.24 mm) than leafed broadleaved trees (D50_DR of 4.32 mm). Canopy drip was much larger in diameter under woody drip points (D50_DR of 5.92 mm) than leafed broadleaved trees. Based on throughfall volume, the percentage of canopy drip was significantly different between conifers, leafed broadleaved trees, leafless broadleaved trees, and woody surface drip points (p ranged from <0.001 to 0.005). These findings are partly attributable to differences in canopy structure and plant surface characteristics between plant functional types and canopy state (leaf, leafless), among other factors. Hence, our results demonstrating the importance of drop‐size‐dependent partitioning between coniferous and broadleaved tree species could be useful to those requiring more detailed information on throughfall fluxes to the forest floor.

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