Nitrogen's dominant role in global organic aerosol absorption revealed

A collaborative research team has introduced a nitrogen-centric framework that explains the light-absorbing effects of atmospheric organic aerosols. Published in Science, this study reveals that nitrogen-containing compounds play a dominant role in the absorption of sunlight by atmospheric organic aerosols worldwide. This discovery signifies a major step towards improving climate models and developing more targeted strategies to mitigate the climate impact of airborne particles.

Atmospheric organic aerosols influence climate by absorbing and scattering sunlight, particularly within the near-ultraviolet to visible range. Due to their complex composition and continuous chemical transformation in the atmosphere, accurately assessing their climate effects has remained a challenge.

The study was jointly led by Prof. Fu Tzung-May, Professor of the School of Environmental Science and Engineering at Southern University of Science and Technology (SUSTech) and National Center for Applied Mathematics Shenzhen (NCAMS), and Prof. Yu Jianzhen, Chair Professor of the Department of Chemistry and the Division of Environment and Sustainability at Hong Kong University of Science and Technology (HKUST).

"Traditional models adopt a carbon-centric approach, merely considering the chemical modification of organic aerosols through a uniform treatment of the bulk carbon element. This methodology lacks efficacy in capturing the relationship between the sources, evolution, and light-absorbing properties of atmospheric organic matter. For the first time, we have quantified the global abundance of light-absorbing nitrogen-containing components in organic aerosols—termed brown nitrogen (BrN)—and revealed how BrN's optical properties vary with chemical composition," explained Prof. Fu.

"Our research shows that the global average direct radiative effect of BrN is 0.034 watts per square meter. BrN contributes to about 70% of the global light-absorbing effects by organic aerosols, and its chemical evolution is the primary driver of spatiotemporal variations in organic aerosol light absorption," added Dr. Li Yumin, the first author of the study and a Ph.D. graduate in Environmental Science, Policy and Management from the HKUST-SUSTech joint Ph.D. program.

The findings underscore the necessity of incorporating nitrogen-containing compounds into future climate and air quality models. With wildfires projected to become more frequent in a future warming climate, emissions of more highly light-absorbing BrN aerosols are expected to increase, further exacerbating climate warming. This introduces a previously unrecognized positive feedback mechanism.

"This work provides a fundamental shift in how we view organic aerosol absorption globally. By identifying nitrogen as the key element, we can better understand Earth's climate-chemistry interactions," said Prof. Yu.

"Understanding these interactions, as well as identifying other light-absorbing organic compounds that do not contain nitrogen, is crucial for improving atmospheric models and developing more effective air pollution control strategies."

By revealing the key role of nitrogen-driven aerosol absorption, the study offers a more accurate framework for predicting climate change impacts and guiding mitigation strategies.