| 11 Sep 2025
Leveraging PMF Time Series Characteristics from Multi-PAMS Measurements for NMHC Source Investigation and Ozone Formation Insights
Abstract. Ozone pollution is a persistent concern in Taiwan’s Kaoping region, where high industrial emissions contribute to poor air quality. Although non-methane hydrocarbons (NMHCs) are key ozone precursors, their sources and seasonal dynamics remain insufficiently resolved in this complex environment. This study aimed to characterize NMHC sources and quantify their contributions to ozone formation across seasons using high-resolution measurements from three Photochemical Assessment Monitoring Stations (PAMS) combined with Positive Matrix Factorization (PMF). Eight distinct source profiles were resolved, including petrochemical factors I & II, refinery, gasoline evaporation, mixed sources (vehicular/solvent), acetylene, aged air mass, and biogenic emissions. The model effectively captured source-specific signatures, notably the acetylene factor at Linyuan (R² = 0.99 with observations), serving as an intrinsic check on PMF performance. Source contributions varied by site and season, with the petroleum industry as the dominant contributor (33–71 %), especially at Xiaogang, while aged air mass (12–30 %) and mixed sources (2–29 %) also played important roles. Despite petroleum dominance, highly reactive species in the mixed source factor drove higher ozone formation potential (OFP). Seasonal and pollution-level analyses revealed that even under moderate ozone conditions (MDA8 40–60 ppb), urban-industrial emissions remained significant contributors to OFP. These findings advance understanding of source-specific NMHC dynamics and highlight the value of multi-site, year-round monitoring for constraining ozone precursor sources. The results underscore the need to prioritize controls on petroleum and urban-industrial emissions to mitigate ozone in industrialized regions.
Manuscript title: Leveraging PMF Time Series Characteristics from Multi-PAMS Measurements
for NMHC Source Investigation and Ozone Formation Insights
Authors: Nguyen et al.
Summary
This manuscript presents a comprehensive source apportionment study of non-methane
hydrocarbons (NMHCs) in Taiwan’s Kaoping region using high-resolution year-round
measurements from three Photochemical Assessment Monitoring Stations (PAMS). Positive
Matrix Factorization (PMF) was applied to resolve eight distinct NMHC source factors,
complemented by Conditional Probability Function (CPF) analysis and a novel “triggered backtrajectory”
approach based on episodic peaks in PMF time series. The study finds that
petroleum and mixed (vehicular/solvent) sources dominate NMHC contributions and ozone
formation potential (OFP), with significant influence even during moderate ozone days.
The manuscript is timely, methodologically innovative, and policy-relevant. It provides strong
observational evidence and demonstrates a refined framework for linking receptor modeling
with spatial source attribution. However, there are some improvements necessary regarding
methodological uncertainty and interpretive depth, which should be addressed before
publication. This amounts to a minor revision.
1. Dependence on PMF and CPF assumptions
o The analysis relies on PMF, which is sensitive to input selection, number of
factors, and uncertainty estimates. While stability tests are mentioned, the
details of these test are not given and unclear what test are done (e.g., factor
rotations, influence of excluded low-S/N species). This would strengthen
confidence in the robustness of source identification.
o The model stability of the CPF could be visualized.
o The inability to fully separate vehicular and solvent sources is acknowledged.
However, this limitation has important implications for regulatory application
and should be discussed more explicitly in the context of control strategies.
2. Treatment of Uncertainty
o Uncertainty quantification appears limited. For example, details of the OFP
estimates are not shown or explained and the specific chemistry assumptions
are not mentioned. Needs to be added.
3. Interpretation of Moderate Ozone Days
o The finding that mixed sources dominate OFP under moderate ozone conditions
is highly relevant, but the mechanistic explanation is underdeveloped. Are these
results consistent with VOC-limited regimes? How do meteorological conditions
(e.g., mixing height) shape these patterns? Expanding the discussion would
enhance both scientific and policy relevance.
Technical Comments
1. Abstract and Summary
o The abstract is long and technical. Consider reducing methodological detail in favor of emphasizing findings and policy implications.
2. Figures
o Some figures (e.g., Fig. 3, Fig. S3) are very information-heavy. Simplifying or providing summary schematics could aid readability.
o S7 legend not readable, S5a vertical axis units are missing.
3. Literature Context
o While many relevant studies are cited, the discussion could further situate the work in the context of ozone regime sensitivity studies (VOC- vs. NOx-limited conditions), which are critical for interpreting the results.
Recommendation
Minor revision
This is a strong and innovative paper that makes a meaningful contribution to atmospheric chemistry and air quality management. However, addressing the above issues—particularly uncertainty analysis, interpretation regarding ozone formation under moderate conditions, and clearer presentation of policy-relevant results—would further strengthen the manuscript.