Decadal Evolution of Visibility in Beijing: Sources and Their Implications for Shifting Perspectives on Haze

Abstract. Atmospheric visibility is a fundamental indicator of air quality, and its degradation is governed by aerosol light extinction, with implications for radiation balance, climate, and public health. Over the past decade, PM_2.5 in China has declined substantially, yet visibility has often improved more slowly, and how changing aerosol composition and atmospheric water, through hygroscopic growth and hydrometeorological extinction, contribute to this lag remains incompletely quantified. Here we quantify the sources and decadal evolution of atmospheric extinction in Beijing (2013–2022) using hourly observations of meteorology, PM_2.5 and aerosol chemical composition within an improved IMPROVE framework that explicitly accounts for hydrometeorological extinction. PM_2.5 decreased from 97.0 to 31.1 µg/m³and annual visibility rose from 12.8 to 28.0 km, while haze frequency declined and fog frequency increased. Particulate extinction remained dominant (55.6 %–59.7 %), but its structure shifted: dry pollutant extinction decreased while hygroscopic extinction, driven by rising nitrate and humidity, rose from 9.4 % to 16.0 %. By 2022, hydrometeorological and hygroscopic extinction together accounted for 73.3 % of the residual extinction. During haze, particulate extinction proportion has declined since 2016 as the rise in nitrate extinction did not offset the larger decline in organic matter, weakening the visibility – PM_2.5 correlation. These results show that natural and composition driven extinction increasingly controls visibility, implying that existing haze criteria may need revision and revealing a nitrate-amplified hygroscopic feedback with global relevance for cities dominated by secondary inorganic aerosols.