Semi-arid regions are characterized by water scarcity and high sensitivity to climate change. However, there is a severe lack of observational research on ice-nucleating particles (INPs) in these areas, leading to a limited scientific understanding of the concentration, sources, and activity of INPs. Here, we report the INP number concentration, surface active-site density (n(s)), and chemical compositions (water-soluble ions and metal elements) of urban particles in different size classes in Lanzhou, a typical city located in a semi-arid region. The results indicate that the particulate pollution in Lanzhou exhibited characteristics of a mixture of dust and anthropogenic pollutants, even during clean periods. The measured concentration of immersion-mode INPs increased with decreasing temperature, ranging from 0.05 to 19.60 L-1 between -25 degrees C and -10 degrees C. At three representative temperatures (-10, -15, and -20 degrees C), the average concentrations were 0.05 +/- 0.04 L-1, 0.49 +/- 0.43 L-1, and 19.60 +/- 5.78 L-1, respectively. Due to the persistent presence of dust particles in the background atmosphere of Lanzhou, INP concentrations are moderately elevated compared to regions dominated by anthropogenic pollution. Chemical composition analysis reveals a notably high proportion of calcium ions and a low proportion of secondary inorganic ions. This characteristic indicates that calcium ions mainly originate from the limited dissolution of calcium carbonate, during dust transport to relatively dry semi-arid regions, low relative humidity inhibits the aqueous-phase chemical reactions between gaseous pollutants and dust surfaces (e.g., calcium carbonate), thereby impeding the formation of secondary products such as calcium nitrate and ammonium nitrate. The relationship between chemical composition and INP concentration reveals that certain metal ions (calcium and magnesium ions) exhibit a strong correlation with INPs in supermicron particles, while secondary inorganic ions show no significant correlation with INPs. This suggests that the ice-nucleating ability of particles in Lanzhou is likely dominated by transported dust, while the contribution of anthropogenic pollution may be limited. Finally, we propose a new parameterization scheme for INP activity that is based on size-resolved nucleation properties (n(s)) and is applicable to mixed conditions of dust and anthropogenic pollution.