Key Takeaways & Executive Findings
- •• • TVOC concentrations in Garage B reached 2398.1 μg·m−3 (weekday) and 3401.6 μg·m−3 (weekend), exceeding typical indoor levels by orders of magnitude, indicating severe VOC accumulation in commercial underground garages. • • CO concentrations peaked at 10.1 mg·m−3 (Garage A) and 12.6 mg·m−3 (Garage B), both surpassing the Chinese 1-h indoor limit of 10 mg·m−3, posing acute exposure risks during rush hours. • • Non-carcinogenic hazard indices (HI) were 0.03 and 0.18, below the EPA safety threshold of 1, yet carcinogenic risks reached Level II (Garage A) and Level III (Garage B), driven by benzene, 1,2-dichloroethane, and naphthalene/ethylbenzene, necessitating priority control. • • BTEX compounds dominated VOC profiles, accounting for >90% (Garage A) and >70% (Garage B) of TVOCs, highlighting gasoline combustion and evaporation as primary sources, with implications for targeted mitigation strategies.
Abstract
This study investigated air pollution and associated health risks in two underground parking garages located in educational and commercial districts of Nanjing, China. Concentrations of non-methane hydrocarbons (NMHC), volatile organic compounds (VOCs), carbon monoxide (CO), and nitrogen oxides (NOx) were monitored. NMHC levels ranged from 0.35–0.55 mg·L−1 (as C) in Garage A and 0.36–1.75 mg·L−1 (as C) in Garage B, peaking during evening rush hours. A total of 23 VOC species were identified, including benzene, toluene, ethylbenzene, xylenes, dichloromethane, and 1,2-dichloroethane. Benzene series compounds constituted over 90% and 70% of total VOCs (TVOCs) in Garages A and B, respectively. Daily average TVOC concentrations were 146.0 μg·m−3 (weekday) and 49.7 μg·m−3 (weekend) in Garage A, and 2398.1 μg·m−3 and 3401.6 μg·m−3 in Garage B. Maximum CO concentrations reached 10.1 mg·m−3 and 12.6 mg·m−3, exceeding the Chinese indoor standard of 10 mg·m−3 (1-h). NOx levels also exceeded standards. Non-carcinogenic hazard indices (HI) were 0.03 and 0.18, below the EPA threshold of 1. However, carcinogenic risks reached Level II and III, with primary contributors being benzene, 1,2-dichloroethane, and naphthalene in Garage A, and ethylbenzene, benzene, and 1,2-dichloroethane in Garage B. The findings indicate potential health threats to garage users, necessitating enhanced ventilation and exposure mitigation.
1. Introduction
Urbanization and the surge in vehicle ownership have intensified parking demand, particularly in densely populated cities where land is scarce. Underground garages have become ubiquitous solutions, yet their semi-enclosed or enclosed structures impede natural ventilation, leading to the accumulation of vehicular emissions. Previous studies in Hong Kong and Baoding have documented elevated levels of VOCs, CO, and particulate matter in such facilities, often exceeding outdoor concentrations. However, comprehensive assessments of health risks, especially carcinogenic risks from specific VOCs, remain limited, particularly in Chinese cities with distinct traffic patterns and garage designs.
This study addresses the gap by conducting a systematic monitoring campaign in two representative underground garages in Nanjing—one in an educational district and another in a commercial district. By measuring NMHC, VOCs, CO, and NOx, and performing component-specific health risk evaluations, the research identifies pollution characteristics and quantifies non-carcinogenic and carcinogenic risks. The findings provide critical data for designing ventilation systems and formulating regulatory guidelines to protect public health in underground parking environments.
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CHEN Huiming, CHU Xu, ZHANG Jian, LONG Chao (2026). Pollution Characterization and Health Risk Assessment of VOCs, CO, and NOx in Underground Garages. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2024112703
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Frequently Asked Questions
What are the peak periods for VOC pollution in underground garages, and how do they vary between educational and commercial districts?
In Garage A (educational district), VOC concentrations peaked during morning and evening rush hours, while Garage B (commercial district) peaked during midday and evening rush hours. Both garages exhibited maximum VOC levels during evening rush hours, likely due to increased vehicle turnover and engine idling.
How do the measured CO concentrations compare to regulatory limits, and what are the potential acute health implications?
Maximum CO concentrations were 10.1 mg·m−3 (Garage A) and 12.6 mg·m−3 (Garage B), both exceeding the Chinese indoor standard of 10 mg·m−3 (1-h average). Such levels can cause symptoms like headaches and dizziness in sensitive individuals, especially during prolonged exposure.
What are the primary VOC species contributing to carcinogenic risk, and what are their concentration ranges?
The top contributors to carcinogenic risk were benzene, 1,2-dichloroethane, and naphthalene in Garage A, and ethylbenzene, benzene, and 1,2-dichloroethane in Garage B. While specific concentrations are not detailed in the abstract, the risk levels (II and III) indicate significant exposure, warranting source control and ventilation improvements.
How do the non-carcinogenic hazard indices (HI) compare between the two garages, and what does this imply for regulatory action?
HI values were 0.03 (Garage A) and 0.18 (Garage B), both below the EPA threshold of 1, indicating no significant non-carcinogenic risk. However, the higher HI in Garage B suggests a greater cumulative effect from multiple VOCs, which may require attention if concentrations increase.
What are the implications of the high TVOC concentrations in Garage B for ventilation system design?
Garage B's TVOC concentrations (up to 3401.6 μg·m−3) are substantially higher than Garage A's, indicating that commercial garages with higher traffic volumes require more robust ventilation systems, possibly with demand-controlled operation during peak hours to reduce exposure.
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