Variability and vertical structure of gaseous air quality indicators above urban areas: IAGOS in-situ profiling of nitrogen oxides, ozone, and carbon monoxide

Nitrogen oxides (NO_X), ozone (O₃), and carbon monoxide (CO) are important air quality indicators which have anthropogenic and natural sources at ground (e.g.: transport emissions, industry, agriculture, biomass burning) and within the troposphere (e.g.: lighting, aircraft emissions). Furthermore, their concentrations in the atmosphere are strongly affected by photochemistry. The European Research Infrastructure IAGOS (www.iagos.org) is using in-service passenger aircraft as observation platforms, equipped with instrumentation for measuring gaseous species, aerosols, and cloud particles. IAGOS monitors the vertical profiles of climate and air quality relevant trace gases like CO, O₃, NO, NO₂ and NO_X near airports of highly populated urban areas (e.g.: Frankfurt (Main) and Paris) during take-off and landing. These profiles provide essential information about the chemical composition of the lower troposphere, which is not available from surface-based stations or remote sensing instrumentation.

Here, we characterize the variability and the vertical structure of these trace gases in the background atmosphere in the lower free troposphere that interacts with the urban boundary layer. In addition, layers of enhanced pollution level can be detected that were advected from distant source regions and have the potential to affect the urban air quality at the receptor site due to downmixing. This data provides valuable information that is complementary to the surface-based air quality network stations, facilitating the link to high-resolution models and satellite observations, where IAGOS can provide information about e.g., the vertical profile of the NO to NO₂ ratio. The latter being difficult to retrieve from remote sensing measurements.

Acknowledgments: This work is part of the RI-URBANS project and has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 101036245. We thank all airlines contributing to IAGOS, in particular Deutsche Lufthansa and Lufthansa Technik for enabling the 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.