Natural halogens are estimated to destroy 10–20 % of tropospheric O3. This study uses an Earth system model to project varying natural halogen emissions and investigate their impact on tropospheric O3 over the 21st century.

Photograph by Alfons Puertas / Observatorio Fabra) New research, led by CSIC, CONICET, NCAR and Lancaster University, shows that emissions of natural halogens (chlorine, bromine and iodine) buffer the increase in global tropospheric ozone (O3), an air pollutant and greenhouse gas, as climate changes during the 21st century. At present, natural halogens (dominated by ocean emissions) are estimated to destroy 10–20 % of global tropospheric O3 burden.

The findings in a new Nature Climate Change paper reveal a strong buffering capacity of natural halogens controlling tropospheric O3, as the climate warms. In this century, the atmosphere and its composition will experience profound disturbances associated with socio-economic developments, such as changes in greenhouse gas and pollutant emissions. Notably, halogen-driven tropospheric O3 destruction is projected to remain unchanged.

In this study, researchers explored long-term simulations using a state-of-the-art Earth system model to project varying natural halogen emissions and investigate their impact on tropospheric O3 abundances over the 21st century. The role that different drivers play on the future atmosphere results in highly heterogeneous tropospheric O3 destruction with marked hemispheric, regional, and vertical asymmetries. Moreover, the largest O3 losses due to natural halogens (up to 70 % compared to present) are predicted over polluted coastal regions, with important benefits for air quality.

The authors of the study hope that these findings will open a “new” focus of research on natural halogen chemistry –as a key component of the troposphere– in coming years, which destroys a large fraction of O3 at the present and will determine its future abundance and distribution in an ever-changing atmosphere.

Fernando Iglesias-Suarez, Alba Badia, Rafael P. Fernandez, Carlos A. Cuevas, Douglas E. Kinnison, Simone Tilmes, Jean-François Lamarque, Ryan Hossaini and Alfonso Saiz-Lopez. Natural halogens buffer tropospheric ozone in a changing climate. Nature Climate Change. DOI: 10.1038/s41558-019-0675-6