Key Takeaways & Executive Findings
- •• • TVOCs mass concentration averaged (27.29 ± 15.96) μg·m−3, with alkanes (50.3%) dominant; key species propane, ethane, methanethiol, and ethylene require targeted control for ozone mitigation. • • OFP reached (64.30 ± 66.41) μg·m−3, with alkenes (63.5%) as main contributor; ethylene, propylene, and m/p-xylene are priority reactive species for reducing ozone formation. • • Daytime photochemical loss of VOCs was 2.40 μg·m−3, with alkenes (67.1%) dominating; correction for this loss is essential to avoid underestimating reactive species in source apportionment. • • PMF based on initial concentrations identified vehicle emissions (56.2%), solvent usage (21.5%), combustion (8.9%), industrial (7.5%), and natural sources (5.9%); compared to uncorrected data, vehicle, combustion, and solvent contributions decreased, while industrial increased, and a natural source emerged.
Abstract
Online measurements of volatile organic compounds (VOCs) were conducted in the central urban area of Shenyang from June 1 to August 31, 2022, to analyze concentration levels and ozone formation potential (OFP). The initial concentrations of VOCs were estimated using the photochemical age parameter method to correct for photochemical losses. Positive matrix factorization (PMF) was applied for source apportionment. The average mass concentration of total VOCs (TVOCs) was (27.29 ± 15.96) μg·m−3, with alkanes (50.3%) as the dominant component; key species included propane, ethane, methanethiol, and ethylene. The OFP of TVOCs was (64.30 ± 66.41) μg·m−3, with alkenes (63.5%) as the main contributor; key reactive species were ethylene, propylene, m/p-xylene, toluene, and isoprene. Daytime photochemical loss of VOCs reached 2.40 μg·m−3, with alkenes (67.1%) dominating. PMF based on initial concentrations identified five major sources: vehicle emissions (56.2%), solvent usage (21.5%), combustion sources (8.9%), industrial emissions (7.5%), and natural sources (5.9%). Compared to PMF results based on directly monitored concentrations, contributions from vehicle emissions, combustion sources, and solvent usage decreased, while industrial emissions increased. The organic chemical industry source was not identified, and a new natural source contribution was recognized. These findings underscore the importance of photochemical loss correction in source apportionment and highlight key species and sources for ozone pollution control in Shenyang.
1. Introduction
Urban ozone pollution remains a critical environmental challenge, with volatile organic compounds (VOCs) serving as key precursors. Accurate source apportionment of VOCs is essential for designing effective control strategies. However, conventional source apportionment using measured concentrations often underestimates the contribution of highly reactive species due to photochemical losses during transport. This leads to misallocation of sources, particularly for reactive alkenes and aromatics, which are major contributors to ozone formation. Existing studies in Chinese cities have applied PMF to measured data, but few have corrected for photochemical aging, potentially skewing results.
This study addresses this bottleneck by applying a photochemical age parameter method to estimate initial VOC concentrations before PMF analysis. Conducted in Shenyang's central urban area during summer 2022, the approach corrects for photochemical losses, providing a more realistic assessment of source contributions. The results reveal significant shifts in source apportionment compared to uncorrected data, including the emergence of natural sources and altered industrial contributions. This methodology offers a more robust framework for identifying priority control targets in ozone-polluted urban atmospheres.
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CHI Haorui, SU Congcong, JIANG Boqi, GUAN Jingwen, CHEN Siyu, YU Xingna (2026). Source Apportionment of Ambient VOCs in Summer in Urban Shenyang Based on Photochemical Loss Correction. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025041105
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Frequently Asked Questions
How does photochemical loss correction affect the source apportionment results compared to using measured concentrations?
Correcting for photochemical losses using the photochemical age method increased the contribution of industrial emissions from an unidentified level to 7.5%, while decreasing vehicle emissions from an uncorrected value to 56.2%, combustion sources to 8.9%, and solvent usage to 21.5%. Additionally, a natural source contribution of 5.9% emerged, which was not identified in the uncorrected PMF analysis.
What are the key reactive species and their contributions to ozone formation potential (OFP) in summer in Shenyang?
The total OFP was (64.30 ± 66.41) μg·m−3, with alkenes contributing 63.5%. The top three species were ethylene, propylene, and m/p-xylene. These species should be prioritized for emission control to mitigate ozone pollution.
What is the magnitude of photochemical loss and which VOC groups are most affected?
The daytime photochemical loss of VOCs was 2.40 μg·m−3. Alkenes accounted for 67.1% of this loss, followed by aromatics (16.6%) and alkanes (15.9%). This indicates that alkenes are the most reactive group and are significantly underestimated in ambient measurements.
How was the initial concentration estimated and what assumptions are involved?
The photochemical age parameter method was used, which relies on the ratio of reactive to less reactive species (e.g., xylenes to ethylbenzene) to estimate the degree of photochemical aging. This method assumes that the emission ratio is known and that the atmospheric chemistry follows pseudo-first-order kinetics. The approach corrects for losses of individual VOCs based on their reaction rate constants with hydroxyl radicals.
What are the implications for ozone control strategies in Shenyang?
The results indicate that vehicle emissions are the dominant source (56.2%), followed by solvent usage (21.5%). Control measures should focus on reducing emissions of alkenes and aromatics from these sources, particularly ethylene, propylene, and xylenes, to effectively lower ozone formation potential.
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