Key Takeaways & Executive Findings
- •• • Temperature-dependent hourly allocation coefficients for VOCs emissions from oil depots were established: coefficient peaks at 0.068 for temperatures >14 °C and drops to 0.007 for temperatures <8.5 °C, enabling seasonally accurate emission inventories. • • Annual VOCs emissions from the studied depot were 256.13 t, with summer (108.89 t) contributing 42.51% and winter (12.54 t) only 4.90%, a seasonal disparity of 8.68-fold that must be captured in air quality modeling. • • Dynamic source strength modeling increased the maximum hourly VOCs concentration by 55.12% (from 1445.8 to 2242.7 μg/m³) and expanded the atmospheric environmental protection distance by 450 m (from 0 to 450 m) compared to constant source assumptions. • • The exceedance area under dynamic conditions was 0.03 km², whereas constant source modeling predicted zero exceedance, highlighting the risk of underestimating health impacts if temporal variability is ignored.
Abstract
To address the inadequacy of existing temporal emission allocation coefficients for oil storage, transportation, and sales sources in regions with distinct seasonal temperature variations, this study focused on a large oil depot in Northwest China. A method for establishing temperature-dependent hourly allocation coefficients for VOCs emissions was proposed, revealing a positive correlation between ambient temperature and emission coefficients. The coefficient peaked at 0.068 when temperatures exceeded 14 °C and dropped to a minimum of 0.007 below 8.5 °C. Annual VOCs emissions totaled 256.13 t, with summer contributing 108.89 t (42.51% of annual total) and winter only 12.54 t (4.90%), making summer emissions approximately 8.68 times higher than winter. Using CALPUFF dispersion modeling, dynamic source strength scenarios produced a maximum hourly concentration of 2242.7 μg/m³, a 55.12% increase over the constant source strength scenario (1445.8 μg/m³). The area of exceedance increased by 0.03 km², and the atmospheric environmental protection distance extended by 450 m, from 0 m to 450 m. These results demonstrate that conventional constant emission assumptions underestimate peak concentrations and protection distances, posing health risks to nearby residents. The study provides a scientific basis for localized emission regulation and improved environmental protection distance calculations.
1. Introduction
Current regulatory frameworks for assessing atmospheric environmental protection distances around oil depots rely on steady-state emission assumptions, as stipulated in China's HJ 2.2—2018 guidelines. However, volatile organic compound (VOCs) emissions from storage tanks are strongly influenced by meteorological factors, particularly ambient temperature, which exhibits significant diurnal and seasonal fluctuations in continental climates such as Northwest China. The conventional constant source strength approach fails to capture these dynamics, potentially masking peak concentration events and leading to underestimated protection distances. This creates a critical gap in safeguarding public health, as residents near depots may be exposed to higher pollutant levels than predicted.
To bridge this gap, the 2024 T/CSES 144—2024 guidelines introduced hourly emission allocation coefficients for oil storage sources, but these coefficients are generic and not tailored to regional temperature patterns. This study addresses that limitation by developing a localized, temperature-dependent allocation coefficient method for a large oil depot in Northwest China. By integrating real meteorological data and dynamic emission profiles into CALPUFF dispersion modeling, we quantify the impact of temporal variability on concentration distributions and protection distances. The findings provide a robust scientific basis for revising emission estimation protocols and enhancing environmental management strategies in seasonally variable regions.
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MA Lingyun, TONG Jilong, LIU Yongle, GAO Qingjun, ZHANG Xuezhi (2026). Local Adaptation of Hourly Allocation Coefficients for VOCs Emissions from Oil Depots and Calculation of Atmospheric Environmental Protection Distances. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202605018
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Frequently Asked Questions
How does the proposed temperature-dependent allocation coefficient method improve upon the generic hourly coefficients provided in T/CSES 144—2024?
The generic coefficients assume a fixed diurnal pattern independent of seasonal temperature variations. Our method establishes distinct coefficients for different temperature ranges, with values ranging from 0.007 (below 8.5 °C) to 0.068 (above 14 °C), reflecting the strong positive correlation between temperature and VOCs volatilization. This localized approach ensures that emission inventories capture seasonal extremes, as evidenced by the 8.68-fold difference between summer and winter emissions, which generic coefficients would fail to represent.
What are the implications of using dynamic versus constant source strength for atmospheric environmental protection distance calculations?
Dynamic source strength modeling, which accounts for temporal variability, yields a maximum hourly concentration of 2242.7 μg/m³, a 55.12% increase over the constant source scenario (1445.8 μg/m³). Consequently, the required protection distance extends from 0 m (no exceedance) to 450 m, and the exceedance area increases by 0.03 km². This demonstrates that constant source assumptions underestimate peak concentrations and protection distances, potentially compromising public health safeguards.
How was the CALPUFF model configured to simulate VOCs dispersion from the oil depot?
CALPUFF was used with a grid resolution sufficient to capture near-field concentration gradients. The dynamic source strength was defined using the temperature-dependent hourly allocation coefficients, while the constant source strength used the annual average emission rate. Meteorological inputs included local hourly temperature data to drive the emission variability. The model output was analyzed for hourly maximum concentrations and exceedance areas based on regulatory thresholds.
What are the limitations of this study and how might they affect the generalizability of the findings?
The study relies solely on numerical dispersion modeling without field validation using measured VOCs concentrations. The allocation coefficients are specific to the climatic conditions of Northwest China and may not be directly transferable to other regions without recalibration. Future work should incorporate long-term monitoring data from multiple points around the depot to validate and refine the model predictions.
How can these findings be applied to improve regulatory practices for oil depot siting and emission control?
Regulatory bodies should mandate the use of temperature-dependent emission profiles when calculating atmospheric environmental protection distances for oil depots in regions with significant seasonal temperature variations. This would prevent underestimation of required distances, ensuring that residential areas are adequately protected. Additionally, the methodology can be adapted to other volatile organic compound sources influenced by meteorological factors.
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