Robust Evidence of ¹⁴C, ¹³C, and ¹⁵N Analyses Indicating Fossil Fuel Sources for Total Carbon and Ammonium in Fine Aerosols in Seoul Megacity

Abstract

Carbon- and nitrogen-containing aerosols are ubiquitous in urban atmospheres and play important roles in air quality and climate change. We determined the 14 C fraction modern ( f M ) and δ 13 C of total carbon (TC) and δ 15 N of NH 4 + in the PM 2.5 collected in Seoul megacity during April 2018 to December 2019. The seasonal mean δ 13 C values were similar to −25.1‰ ± 2.0‰ in warm and −24.2‰ ± 0.82‰ in cold seasons. Mean δ 15 N values were higher in warm (16.4‰ ± 2.8‰) than in cold seasons (4.0‰ ± 6.1‰), highlighting the temperature effects on atmospheric NH 3 levels and phase-equilibrium isotopic exchange during the conversion of NH 3 to NH 4 + . While 37% ± 10% of TC was apportioned to fossil-fuel sources on the basis of f M values, δ 15 N indicated a higher contribution of emissions from vehicle exhausts and electricity generating units (power-plant NH 3 slip) to NH 3 : 60% ± 26% in warm season and 66% ± 22% in cold season, based on a Bayesian isotope-mixing model. The collective evidence of multiple isotope analysis reasonably supports the major contribution of fossil-fuel-combustion sources to NH 4 + , in conjunction with TC, and an increased contribution from vehicle emissions during the severe PM 2.5 pollution episodes. These findings demonstrate the efficacy of a multiple-isotope approach in providing better insight into the major sources of PM 2.5 in the urban atmosphere.

Characterization of the PM2.5 aerosol fraction monitored at a suburban site in south-eastern Italy by integrating isotopic techniques and ion beam analysis

“…The δ 15 N values generally increase with increasing air pollution. On the other hand, the content of C (PC) in the sampled filters was highly variable and included in the range from 4.9 to 53.4 μg, while δ 13 C presented a limited variability, in the range from −24.41 to −26.70‰, generally consistent with the combustion of biomass (−26.7 ± 1.8‰) and with vehicular traffic (from −25.5 ± 1.3‰ for liquid fossil fuels to −23.4 ± 1.3‰ for solid fossil fuels), according to the values reported by Lim et al (2022).…”

Limitations in representation of physical processes prevent successful simulation of PM<sub>2.5</sub> during KORUS-AQ

“…In South Korea, and generally East Asia, NH 4 NO 3 is limited by availability of HNO 3 . This is due to high lev-els of NH 3 (∼ 10 ppb) observed in East Asia, attributable to non-agricultural sources such as transportation (Song et al, 2009;Phan et al, 2013;Link et al, 2017;Sun et al, 2017;Chang et al, 2019;Lim et al, 2022). The model reproduces the expected high concentration of NH 3 with an average of 9 ppb at Olympic Park.…”

Sources of NH4+ in PM2.5 and Their Seasonal Variations in Urban Tianjin China: New Insights From the Seasonal δ15N Values of NH3 Source

“…This discrepancy suggests that the concentration of PM 2.5 was also influenced by other components (e.g., carbon components, organic matter, etc.) (Lim et al., 2022; T. Liu et al., 2023).…”

“…Similar seasonal variations in δ 15 N‐NH 4 + have been documented in Xiamen (S. P. Wu et al., 2019) and Harbin (Sun et al., 2021). The variability of δ 15 N‐NH 4 + values in PM 2.5 was predominantly influenced by the isotope exchange equilibrium fractionation factor (ε) associated with temperature, isotopic fractionation effects during NH 3 /NH 4 + transformation processes, and emission sources (Lim et al., 2022). One would expect the δ 15 N‐NH 4 + values to become more positive as T decreases if they were predominantly controlled by ε (Z. Zhang et al., 2019), this study observed a moderate linear positive correlation between δ 15 N‐NH 4 + values and T (Figure S8a in Supporting Information ), suggesting that variations in ε were not the primary driver of the seasonal changes in δ 15 N‐NH 4 + values.…”