Integrated modeling of urban–scale pollutant transport: application in a semi–arid urban valley, Northwestern China

Abstract

Air pollution in urban areas is related not only to emission sources but also to atmospheric dispersion and transport conditions. Knowledge of pollutant transport pathways, potential source regions and their relative contribution to pollution levels in a city is thus very useful for urban planning and development of effective regulatory and mitigation strategies. In this study, the Hybrid Single–Particle Lagrangian Integrated Trajectory (HYSPLIT) model driven by high resolution (1km × 1km) meteorological fields from the Weather Research & Forecasting (WRF) model was used to identify the relationship between atmospheric transport patterns and daily pollutant concentrations on urban scale, with a case study in Lanzhou–an urban valley in Northwestern China. Trajectories calculated by HYSPLIT model for winter months (December, January and February) of 2002–2008 were analyzed using Ward’s hierarchical method to identify dominant transport pathways leading to elevated pollutant concentrations in urban Lanzhou. Potential source locations and their relative contribution to pollution levels were evaluated with the help of potential source contribution function (PSCF) analysis and the concentration–weighted trajectory (CWT) method. The transport pathways from the northeast of the urban center and from the west and the east county were identified as the most important pathways leading to high pollutant concentrations in urban Lanzhou, with potential source areas located in the west and the east to the urban center. The contribution of potential source regions was more than 200 µg m–3, 120 µg m–3 and 60–80 µg m–3 to the PM10, SO2 and NO2 loadings, respectively, which is closely related to emission source characteristics in the study area.