Nitric oxide emissions from lakes in the Northern Hemisphere

Abstract. Nitrogen oxides (NO_x = NO + NO₂) are a key player in the nitrogen cycle affecting health and climate. Recent work revealed high nitric oxide (NO) emissions from natural lakes on the Tibetan Plateau, yet the global prevalence and importance of lake emissions remain unclear. Here, we quantify NO emissions from 300 large natural or human-influenced lakes across the Northern Hemisphere (NH) in 2018–2024 summertime early afternoon, based on satellite measurements of tropospheric nitrogen dioxide (NO₂) and an advanced emission inversion algorithm. The average lake emission intensity reaches 0.15 ± 0.32 kg N km^-2 h^-1, nearly four times greater than summertime soil emission intensity from croplands in the NH. The total emissions from all lakes amount to 70.95 ± 13.98 Tons N h^-1, equivalent to twice the anthropogenic emissions in Japan or nearly half of power-sector emissions in China. Emissions from many lakes are each comparable to anthropogenic emissions in global economic hub cities. Such considerable emissions across the NH lakes are either missing (for natural sources) or poorly represented (for anthropogenic sources) in current emission datasets and models. The significance of lake NO emissions calls for improved in-situ measurements and numerical models to better understand such lake-atmosphere interactions and their eco-environmental impacts.