IAGOS in situ observations of NOx in the upper troposphere over the tropical Atlantic

Nitrogen oxides (NO_x), ozone (O₃), and carbon monoxide (CO) are important air quality indicators, while NO_x is also one of the main precursors of O₃. These trace gases have anthropogenic and natural sources at ground level and in the troposphere. At ground level, the main sources are transport emissions, industry, agriculture, and biomass burning. In the troposphere, additional sources include lighting and aircraft emissions and in the upper troposphere, downmixing from the stratosphere also makes a significant contribution to the ozone budget. Furthermore, the abundances of NO_x and O₃ in the troposphere are controlled by photochemistry.

The European Research Infrastructure IAGOS (www.iagos.org) uses in-service passenger aircraft as observation platforms, equipped with instruments to measure gaseous species, aerosols, and cloud particles. Since 2023 an IAGOS-CORE NO_x instrument (Package 2b) is installed aboard an IBERIA Airbus A330-200. Based in Madrid (Spain), this IAGOS-CORE aircraft covers routes to North, but mainly Central and South America. On the routes from Europe to Central and South America, the atmospheric abundances of the climate and air quality relevant trace gases CO, O₃, NO, NO₂, and NO_x were observed in the photochemically active region over the tropical Atlantic over the course of one year. From this unique dataset, we characterize the variability and the horizontal distribution of these trace gases across the Intertropical Convergence Zone and discuss the origin of the observed air masses.   

Acknowledgments: We thank all members of IAGOS-CORE, in particular IBERIA for enabling these IAGOS-CORE observations. The German Federal Ministry of Education and Research (BMBF) is acknowledged for financing the instruments operation and data analysis as part of the joint project IAGOS-D under grant 01LK1301A.