Global Ozone Reduction Driven by Dust‐Catalyzed Halogen Chemistry

Abstract

Tropospheric ozone (O3) influences climate and poses risks to human health and crop productivity. Its distribution is shaped by complex interactions between chemical production, transport, and loss processes, including reactions with naturally occurring halogens. Recent studies have shown that mineral dust represents a catalyst for halogen activation, releasing chlorine and iodine radicals that destroy O3 yet these mechanisms are rarely represented in current atmospheric models. Here, using the Community Earth System Model with explicit chlorine and iodine activation on dust particles, we show that dust‐driven halogen chemistry substantially reduces O3 downwind of major dust source regions. This mechanism drives global annual mean decreases of ∼5% in ground‐level O3 and ∼3% in the tropospheric O3 column, consistent with observed 3%–6% tropospheric O3 column reductions over the tropical Atlantic during high‐dust conditions. Including this process improves the model's ability to detect the observed spatial pattern of tropospheric O3 suppression under high‐dust conditions, particularly in major dust outflow regions. Dust‐driven halogen activation reduces ozone over marine regions, with impacts that propagate inland into agricultural areas. These reductions lower accumulated ozone exposure and improve crop productivity, with the largest improvements (up to 9%) for wheat, rice, and soybeans in southern Asia and North America. Reduced ozone also lowers ozone‐attributable mortality, with the strongest benefits occurring in dust‐influenced regions of Asia. Our results identify that dust‐catalyzed halogen chemistry represents an underrepresented natural ozone sink, with implications for air quality, agricultural productivity, and human health. Projected future increases in dust emissions could further amplify this effect on regional and global ozone budgets.