Distinct Roles of Industrial and Natural Mineral Dust in Aerosol Spectral Absorption in a Semi-Arid Industrial City

Mineral dust frequently coexists with carbonaceous aerosols in the urban ambient atmosphere, yet accurate quantification of its light absorption remains challenging. Conventional absorption apportionment methods based on field observations usually neglect the contribution of mineral dust, resulting in an underestimation of its absorption and concurrent misattribution to carbonaceous aerosols. To address this issue, we integrated optical and chemical measurements into a receptor model using a three-year comprehensive data set from Lanzhou, a semi-arid industrial city in China. The results indicate that natural and industrial dust are significant sources of aerosol absorption, a phenomenon not widely reported in the literature. The contribution of natural dust to aerosol absorption at 370 nm was the highest in spring (12.6%), while that of industrial dust peaked in summer (10.5%), underscoring its distinct seasonal pattern and substantial influence. The absorption Ångström exponent for total dust was 2.24, 1.46, 1.02, and 2.39 in spring, summer, autumn, and winter, respectively. Accounting for total dust absorption improves the mass absorption cross section of organic carbon by up to 59% at 370 nm wavelength. Our study provides novel insights into aerosol spectral absorption and highlights the critical yet previously overlooked role of industrial dust in semi-arid industrial cities.