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- Title
Sources of NH<sub>4</sub><sup>+</sup> in PM<sub>2.5</sub> and Their Seasonal Variations in Urban Tianjin China: New Insights From the Seasonal δ<sup>15</sup>N Values of NH<sub>3</sub> Source.
- Authors
Xiao, Hao; Ding, Shiyuan; Li, Xiaodong
- Abstract
The stable nitrogen isotopic composition (δ15N) has been widely used to quantify sources of ammonium (NH4+) in PM2.5. However, the overlap and uncertainty in δ15N values from different NH3 sources, coupled with their seasonal variability, hinder accurate identification of NH4+ source. Here, the δ15N values of various NH3 source samples collected by the active sampler were determined. Subsequently, we measured the δ15N values of NH4+ in PM2.5, which were collected seasonally in Tianjin. We found that the combustion‐related NH3 (c‐NH3) exhibiting higher δ15N values compared to volatile NH3 (v‐NH3), but all δ15N values was fell within the range reported by previous studies. Furthermore, inconsistent seasonal variations were observed in the δ15N‐NH3 values originating from emissions of agricultural soil and human excreta. The application of the Bayesian isotope mixing model (MixSIAR model) revealed a significant increase in the contribution of v‐NH3 to NH4+ when incorporating current source data, as opposed to previous data, for δ15N of NH3 source. Notably, the contribution of v‐NH3 (53.1%) to NH4+ was almost equivalent to that of c‐NH3 (46.9%) when considering the seasonal δ15N signatures of NH3 source. Additionally, the estimated contribution of v‐NH3 to NH4+ exhibited significant seasonal variability, which is more reasonable than in the non‐seasonal scenario. This study demonstrated that v‐NH3 and c‐NH3 contributed to NH4+ in PM2.5 in Tianjin almost equally, and it is highlighted that the seasonal δ15N values of NH3 sources should be considered when estimating the contributions of different NH3 sources to NH4+ in PM2.5 by the MixSIAR model. Plain Language Summary: Quantifying the source of NH4+ in PM2.5 through δ15N remains disputed, one possible reason was the uncertainty in δ15N values of NH3 sources. This study investigated the δ15N values from different NH3 sources collected by the active sampler, of which the δ15N‐NH3 from agricultural soils and human excreta emissions were characterized by season. Furthermore, we measured the δ15N values of NH4+ in PM2.5 collected seasonally in Tianjin to estimate the source contribution of NH4+ based on the MixSIAR model. Results found that a reasonable source‐resolved structure of NH4+ and their seasonal variations was obtained by the MixSIAR model using the seasonal δ15N data of NH3 source in this study. Specially, the contribution of c‐NH3 was significant overestimated when used the δ15N data of NH3 source from previous studies. Moreover, the estimated contribution of v‐NH3 to NH4+ exhibited significant seasonal variability, which is more reasonable than in the non‐seasonal scenario. These findings showed that the seasonal δ15N values of NH3 sources should be considered when estimating the contributions of different NH3 sources to NH4+ in PM2.5 using the MixSIAR model. Key Points: The δ15N values of six typical NH3 sources was systematically established using the active sampling methodThe δ15N‐NH3 values originating from agricultural soil and human excreta exhibit inconsistent seasonal variationsConsidering the seasonal δ15N variation in NH3 sources may obtained a reasonable seasonal source‐resolved structure of NH4+
- Subjects
TIANJIN (China); AGRICULTURAL pollution; SEASONS; PARTICULATE matter; AGRICULTURE; NITROGEN isotopes
- Publication
Journal of Geophysical Research. Atmospheres, 2024, Vol 129, Issue 9, p1
- ISSN
2169-897X
- Publication type
Article
- DOI
10.1029/2023JD040169