Spatial–Temporal Distribution Characteristics of Emission and Diffusion of Vehicular Pollutants: A Case Study of Expressway Network in Jiangsu Province

To address the growing pollution problem of vehicle exhaust on expressways, a calculation method for the emission and diffusion of vehicular pollutants in expressway network of Jiangsu province was proposed based on the emission inventory of road vehicular pollutants and the CALINE-4 diffusion model. The characteristics of the spatial-temporal distribution were analyzed. The following conclusions can be drawn: (1) In the province's expressway network with various vehicle styles and structures, the largest contributor of CO and HC emissions was Coach Model Ⅰ, contributing 41.26% and 44.32%, respectively; the largest contributor of NO_x and PM_2.5 emissions was Truck Model Ⅴ, contributing 33.32% and 32.52%, respectively. (2) From the vehicle emission level, for Coach Model Ⅰ, the contribution rate of the national stage Ⅰ-Ⅲ vehicle emission standards to the total CO and HC emissions reached 73.56% and 62.05%, respectively; for Truck Models Ⅳ and Ⅴ, the contribution rate of the national stage Ⅲ vehicle emission standard to the total NO_x and PM_2.5 emissions reached 58.73% and 63.25%, respectively. (3) Except for NO_x, the diffusion concentration of vehicular pollutants (CO, PM_2.5, and PM₁₀) in each section of the predicted points was lower than the 1-hour average limiting value taken as Grade Ⅱ on the basis of the Ambient Air Quality Standards (GB3095-2012), which is 10 mg/m³, 75 μg/m³, and 150 μg/m³. (4) From the temporal distribution, the amount of various pollutants showed a double-hump trend, which occurred at 9-10 a.m. and 2-3 p.m. The hourly diffusion concentration of various pollutants in all sections of the province was higher at night (10 p.m. to 4 a.m. the next day) than in the daytime. The proportion of sections exceeding the limit of NO_x diffusion concentrations at night was as high as 75.2%, reaching the peak value at 2-3 a.m. (5) From the spatial distribution, the total CO and HC emissions in the North Network were less than that in the South Network, and the NO_x, PM_2.5, and PM₁₀ emissions in the North Network were higher than those in the South Network, while the emission intensity of all kinds of pollutants in the North Network was significantly higher than that in the South Network. The 1-hour average NO_x concentration in Northern Jiangsu was higher than that in Southern Jiangsu and Middle Jiangsu, with the maximum value of all periods of the day appearing in the section of "Duanzhai Hub-Xinyi Dong" and the minimum value mainly distributing in Middle Jiangsu.