Sulfate burden over the North Atlantic (NATL) exhibits strong seasonality despite no seasonality in anthropogenic sulfur dioxide (SO2) emissions. However, the seasonality of sulfate aerosols over NATL has decreased over the past five decades, likely due to a reduction in the United States (U.S.) SO2 emissions following the Clean Air Act of 1976. We performed atmospheric chemistry and transport model simulations to assess the impact of changing U.S. SO2 emissions between 1970 and 2010 on NATL sulfate burden and radiative forcing. U.S. SO2 emission reductions weakened the North Atlantic sulfate burden’s seasonality by ~20%, primarily due to decreased chemical production and transport in summer. These emission reductions caused a summertime radiative forcing (~2 Wm-2) twice as large as the wintertime forcing. Our findings highlight the complex, season-dependent responses of sulfate burden and radiative effects to regional emission changes.

Phosphorus (P) is an essential nutrient for terrestrial and aquatic ecosystems, with many species limited by P availability for primary productivity. While dust and primary biological aerosols, such as pollen, are shown to be large atmospheric P sources, emissions from phosphatic fertilizer production-comprising of phosphate rock mining, grinding, and chemical processing-remain unquantified. We present the first global estimate of P aerosol emissions from fertilizer production using publicly available production and emission factor data. Present-day annual bioavailable P emissions in the sub-10-micron fraction are ~120 Gg P/year, comparable to dust, but are more directly upwind of P-limited ocean basins like the North Atlantic. Between 2002 and 2022, these emissions increased by 60%, fluctuating with fertilizer production trends. With P demand projected to triple by 2100, understanding this source and its impacts on ecosystems is important.