Cross-phase partitioning of sulfur-nitrogen ratios and aerosol mixing-state evolution based on single-particle observations
- 1Nanjing University of Information Science and Technology (Nanjing, China)
- 2Southeast University (Nanjing, China)
Abstract
The balance between sulfur and nitrogen (S-N) precursors influences secondary aerosol formation, yet its cross-phase links to particle composition and mixing states remain poorly constrained. Here, we integrated single-particle aerosol mass spectrometry (SPA-MS) with pollutant and meteorological observations during winter and summer emission control periods (ECPs) and corresponding normal periods (NPs) in Yangzhou, eastern China. By establishing gas-phase (gSNR), particle-phase (pSNR), and number-based (nSNR) sulfur-to-nitrogen ratio metrics, we combined causal inference with interpretable machine learning to analyze the underlying drivers. During ECPs, reduced NO x emissions alongside relatively stable SO ₂ concentrations elevated gSNR, driving an average ∼ 57 % increase in pSNR across particle classes and a 27 % expansion in mean vacuum aerodynamic diameter ( D va ) relative to NPs. Causal analysis revealed a stepwise propagation of S-N partitioning running sequentially from gas-phase precursors to single-particle chemistry and ultimately to the population mixing state. Particle-resolved chemistry demonstrated that pSNR enrichment was highest in particles containing both black carbon and organic carbon, but markedly lower in BC-free inorganic particles, indicating strong particle-type-dependent aging pathways. Relative humidity (RH) acted as a primary regulator of this cross-phase coupling: below 55 % RH, the SNR metrics decoupled, maintaining substantial chemical heterogeneity across particle classes (externally mixed state); above 85 % RH, aerosol liquid water uptake accelerated gas-particle exchange and multiphase processing, causing the SNR metrics to converge as aerosols evolve toward an internally mixed state. These findings suggest that future air-quality models would benefit from incorporating particle-type heterogeneity and humidity-dependent multiphase processes under shifting emission regimes.
Versions
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BibTeX
@article{dai2026crossphase,
title = {{Cross-phase partitioning of sulfur-nitrogen ratios and aerosol mixing-state evolution based on single-particle observations}},
author = {Yuan Dai and Junfeng Wang and Mindong Chen and Su Zhang and Haiwei Li and Yunjiang Zhang and Yun Wu and Ming Wang and Xinlei Ge},
journal = {Atmospheric Chemistry and Physics},
year = {2026},
month = oct,
doi = {10.5194/acp-26-14015-2026},
url = {https://acp.copernicus.org/articles/26/14015/2026/},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Cross-phase partitioning of sulfur-nitrogen ratios and aerosol mixing-state evolution based on single-particle observations
AU - Yuan Dai
AU - Junfeng Wang
AU - Mindong Chen
AU - Su Zhang
AU - Haiwei Li
AU - Yunjiang Zhang
AU - Yun Wu
AU - Ming Wang
AU - Xinlei Ge
PY - 2026
DA - 2026/10/06
JO - Atmospheric Chemistry and Physics
DO - 10.5194/acp-26-14015-2026
UR - https://acp.copernicus.org/articles/26/14015/2026/
AB - The balance between sulfur and nitrogen (S-N) precursors influences secondary aerosol formation, yet its cross-phase links to particle composition and mixing states remain poorly constrained. Here, we integrated single-particle aerosol mass spectrometry (SPA-MS) with pollutant and meteorological observations during winter and summer emission control periods (ECPs) and corresponding normal periods (NPs) in Yangzhou, eastern China. By establishing gas-phase (gSNR), particle-phase (pSNR), and number-based (nSNR) sulfur-to-nitrogen ratio metrics, we combined causal inference with interpretable machine learning to analyze the underlying drivers. During ECPs, reduced NO x emissions alongside relatively stable SO ₂ concentrations elevated gSNR, driving an average ∼ 57 % increase in pSNR across particle classes and a 27 % expansion in mean vacuum aerodynamic diameter ( D va ) relative to NPs. Causal analysis revealed a stepwise propagation of S-N partitioning running sequentially from gas-phase precursors to single-particle chemistry and ultimately to the population mixing state. Particle-resolved chemistry demonstrated that pSNR enrichment was highest in particles containing both black carbon and organic carbon, but markedly lower in BC-free inorganic particles, indicating strong particle-type-dependent aging pathways. Relative humidity (RH) acted as a primary regulator of this cross-phase coupling: below 55 % RH, the SNR metrics decoupled, maintaining substantial chemical heterogeneity across particle classes (externally mixed state); above 85 % RH, aerosol liquid water uptake accelerated gas-particle exchange and multiphase processing, causing the SNR metrics to converge as aerosols evolve toward an internally mixed state. These findings suggest that future air-quality models would benefit from incorporating particle-type heterogeneity and humidity-dependent multiphase processes under shifting emission regimes.
SN - 1680-7324
ER -