Local Adaptation of Hourly Allocation Coefficients for VOCs Emissions from Oil Depots and Calculation of Atmospheric Environmental Protection Distances
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.