“…Because values were determined by fractional contributions of dominant NH 3 sources from vehicle exhausts, coal combustion, biomass burning, and wastes and fertilizers (, , , and , respectively) and their δ 15 N values (Table S3), and values were determined by fractional contributions of dominant NO x sources from vehicle exhausts, coal combustion, biomass burning, and microbial N cycles (, , , and , respectively) and their δ 15 N values (Table S3; Liu et al, 2017; Song et al, 2019, 2021), , , , , , , , and can be calculated by the Stable Isotope Analysis in R and based on and values, respectively (detailed in Text S2; shown in Figure S3). Then, we calculated relative contributions between combustion‐related NH 3 (c‐NH 3 ) sources (, the sum of , …”