Dust Transport and Local Anthropogenic Emissions Differently Shape Atmospheric Ice-Nucleating Particles: Insights from an Industrial Urban Atmosphere

Abstract. Atmospheric ice-nucleating particles (INPs) are vital for cloud formation, yet the importance of INPs from anthropogenic sources remains poorly understood. We conducted a month-long winter field campaign in Taiyuan, a heavily industrialized city, to quantify INP concentrations (N_INP) and ice nucleation active site density (n_s) of immersion mode INPs, alongside particle size distributions and chemical compositions. Our results indicate that N_INP ranged from 0.0532 to 13.4 L⁻¹ at −15 °C, corresponding to n_s values of 10⁵–10⁷ m⁻². During a dust event, both N_INP (7.47 L⁻¹ ; 95 % CI: 6.64–8.41 L⁻¹) and n_s (1.77 × 10⁷ m⁻² ; 95 % CI: 1.58–1.99 × 10⁷ m⁻²) increased nearly one order of magnitude compared with periods without natural dust influence (1.75 L⁻¹ and 3.89 × 10⁶ m⁻², respectively), highlighting the dominance of long-range transported desert dust. In contrast, during pollution periods, N_INP showed only weak correlations with urban aerosol components like SO₄²⁻, NO₃⁻, and OC (|r| < 0.3). Positive matrix factorization (PMF) identified five PM_2.5 sources: coal combustion and traffic emissions, industry, (anthropogenic) dust, secondary aerosols and fireworks. Although these dominated the PM_2.5 mass, none contributed significantly to INPs. This implies that even in heavily industrialized environments, the direct impact of anthropogenic emissions on INP loading remains limited. In summary, long-range mineral dust transport is the decisive driver of INP enhancements, while traditional anthropogenic fine aerosols contribute minimally. Observed N_INP variability is likely governed by the interplay of episodic coarse-mode inputs and atmospheric processing rather than a single dominant source.