Global Ozone Reduction Driven by Dust-Catalyzed Halogens

Tropospheric ozone (O₃) is an important air pollutant and short-lived climate forcer that influences climate and poses risks to human health and crop productivity. While reactive halogens are known to destroy ozone, the role of mineral dust as a catalyst for halogen activation remains poorly represented in chemistry–climate models. Here we present a global quantitative assessment of ozone reduction driven by dust-catalyzed chlorine and iodine chemistry.

Using the Community Earth System Model (CESM) with explicit dust-induced halogen activation, we show that mineral dust substantially enhances reactive Cl and I production, particularly in marine outflow regions where dust mixes with sea-salt aerosol. This mechanism leads to a global annual mean reduction of ~5% in surface ozone and ~3% in the tropospheric ozone column. Modeled ozone responses are consistent with satellite observations, reproducing observed 3–6% tropospheric ozone column decreases over the tropical Atlantic during high-dust conditions and improving the spatial agreement of ozone responses to dust relative to simulations without dust-halogen chemistry.

Ozone depletion due to this mechanism is strongest over oceanic dust outflow pathways but propagates inland, affecting continental regions far from dust sources. As a result, dust-driven halogen chemistry reduces growing-season ozone exposure (AOT40) across major agricultural regions, increasing crop productivity by up to 9% in South Asia and by 1–7% across parts of Europe, North America, and West Central Asia. Lower ground-level ozone also reduces ozone-attributable premature mortality, with the largest health benefits occurring in densely populated, dust-influenced regions of Asia.

Our results identify dust-catalyzed halogen activation as a previously underrepresented natural global ozone sink with important implications for air quality, agriculture, human health, and the global oxidizing capacity.