Unveiling the Overlooked Inhibitory Effects of Carbon Dioxide on Photochemical Nitrate Decomposition over Photoactive Mineral Dust

Abstract

Carbon emissions lead to an increased greenhouse gas concentration, which, in turn, affects air quality by altering the global climate. Despite its importance, the direct relationship between carbon emissions and the atmospheric reactive nitrogen cycle has been poorly understood. This study provides an in-depth investigation of the effects of CO₂ on the photochemical transformation of nitrates on mineral dust. The results show that CO₂ inhibits the photochemical transformation of nitrate under simulated solar irradiation. Specifically, the NO_x production rate from nitrate photolysis with CO₂ was significantly reduced to 1.17 × 10^–10 mol·s^–1, representing a decrease of 57.8%, compared to that without CO₂ (2.77 × 10^–10 mol·s^–1). This inhibition effect can be primarily ascribed to electron competition and the formation of carbonate/bicarbonate intermediates. Quenching experiments and electron paramagnetic resonance spectroscopy unveiled the crucial role of photogenerated electrons in nitrate photolysis, showing its significant competition with photochemical CO₂ conversion. Additionally, carbonate/bicarbonate intermediates formed during photochemical CO₂ conversion enhance the nitrate stability on mineral dust surfaces, thus, reducing their decomposition rate. This study unveils an overlooked atmospheric process of greenhouse gas participating in the reactive nitrogen cycle, highlighting the unignorable synergistic effects of carbon emissions and air pollution in photochemical reactions.