Key Takeaways & Executive Findings
- •• • Total VOC concentration averaged (9.05 ± 6.24) nmol·mol−1, with alkanes dominating; this baseline is critical for setting emission reduction targets in tropical urban roadside environments. • • PMF source apportionment quantified gasoline/LPG vehicle exhaust as the largest contributor at 49.9%, followed by solvent use/evaporation (26.1%) and diesel exhaust (14.9%), underscoring the need for targeted control of gasoline-related emissions. • • SOAFP was limited, with solvent use/evaporation (35.7%) and gasoline/LPG exhaust (34.6%) as main contributors, indicating that VOC control strategies should prioritize these sources to mitigate secondary organic aerosol formation. • • Diurnal VOC concentrations showed a bimodal pattern aligned with traffic peaks, and T/B and i/n ratios indicated fuel evaporation influence, highlighting the importance of controlling evaporative emissions in hot climates.
Abstract
This study conducted online monitoring of volatile organic compounds (VOCs) at a roadside site on a main arterial road in Haikou, a tropical city, during summer 2023 (June 25–September 30). A total of 56 VOCs were measured. The mean total VOC concentration (φ(TVOCs)) was (9.05 ± 6.24) nmol·mol−1, with concentrations in the order: alkanes > alkenes > aromatic hydrocarbons > alkynes, dominated by light alkanes. Alkenes and aromatic hydrocarbons contributed significantly to atmospheric chemical reactivity, while secondary organic aerosol formation potential (SOAFP) was limited, influenced by both VOC concentrations and temperature. VOC concentrations exhibited a pronounced bimodal diurnal pattern, consistent with traffic peaks. Ratio analysis indicated a Toluene/Benzene (T/B) ratio slightly higher than typical vehicle exhaust values, and an iso-Pentane/n-Pentane (i/n) ratio suggesting fuel evaporation influence. Positive Matrix Factorization (PMF) identified four sources: gasoline/LPG vehicle exhaust (49.9%), solvent use or vehicle evaporation (26.1%), diesel vehicle exhaust (14.9%), and biogenic sources (9.1%). SOAFP was mainly contributed by solvent use/evaporation (35.7%), gasoline/LPG exhaust (34.6%), diesel exhaust (22.0%), and biogenic sources (7.7%). These findings indicate that under tropical summer high-temperature conditions, roadside VOC pollution is predominantly traffic-related, with vehicle evaporation sources non-negligible, providing insights for evaluating vehicular impacts on particulate pollution.
1. Introduction
Urban air quality management faces persistent challenges from volatile organic compounds (VOCs), which are key precursors to ozone and secondary organic aerosols (SOA). In tropical cities, high temperatures and intense solar radiation exacerbate photochemical reactions, yet roadside VOC characteristics and source contributions remain understudied. Existing studies in temperate regions often overlook the enhanced evaporation of fuels and solvents under tropical conditions, leading to inaccurate emission inventories and ineffective control strategies. This research addresses that gap by conducting continuous online monitoring at a roadside site in Haikou, a representative tropical city, during summer.
The experimental protocol integrates high-resolution VOC measurements with advanced source apportionment using Positive Matrix Factorization (PMF), coupled with reactivity and SOA formation potential analyses. By quantifying the contributions of traffic exhaust, fuel evaporation, and biogenic sources, this study provides a robust framework for understanding VOC dynamics in tropical urban environments. The findings directly inform policy on vehicular emission controls and evaporative loss management, offering a scientific basis for mitigating photochemical smog and particulate pollution in similar climatic regions.
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LIN Youjing, XU Wenshuai, ZENG Yurong, ZHOU Xiaopeng, ZHANG Mingshan, MENG Xinxin (2026). Characteristics and Source Apportionment of Volatile Organic Compounds at a Roadside Site in a Tropical City during Summer. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2026012804
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Frequently Asked Questions
What are the dominant VOC sources and their quantitative contributions at the roadside site?
PMF analysis identified four sources: gasoline/LPG vehicle exhaust (49.9%), solvent use or vehicle evaporation (26.1%), diesel vehicle exhaust (14.9%), and biogenic sources (9.1%). These contributions were derived from 56 VOC species measured over the summer period.
How does the high-temperature tropical environment influence VOC composition and SOA formation potential?
The mean TVOC concentration was (9.05 ± 6.24) nmol·mol−1, with alkanes dominating. SOAFP was limited, influenced by both concentrations and temperature. The T/B ratio (slightly above typical exhaust values) and i/n ratio indicated enhanced fuel evaporation, which is exacerbated by high temperatures, leading to a significant contribution from evaporation sources (26.1%) to total VOCs.
What are the implications for ozone and secondary organic aerosol control strategies?
Alkenes and aromatic hydrocarbons contributed significantly to atmospheric reactivity, while SOAFP was mainly from solvent use/evaporation (35.7%) and gasoline/LPG exhaust (34.6%). This suggests that controlling these sources would be most effective in reducing SOA formation, whereas diesel exhaust (22.0%) and biogenic sources (7.7%) are less critical.
How do diurnal variations and traffic patterns affect VOC concentrations?
VOC concentrations exhibited a bimodal diurnal pattern, with peaks corresponding to morning and evening traffic rush hours. This correlation indicates that traffic emissions are the primary driver, and local traffic management policies could influence VOC levels.
What is the reliability of the PMF source apportionment given the limited number of samples?
The study monitored 56 VOCs over a three-month period, providing a robust dataset. PMF resolved four factors with clear source profiles, and the results were consistent with ratio analyses. However, the study does not report uncertainty estimates or bootstrap validation, so the contributions should be interpreted with caution.
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