Observing the two- and three- dimensional distributions of trace gases with the Heidelberger Airborne Imaging DOAS Instrument (HAIDI) on board HALO during the phase II mission EMerGe
Final Report Abstract
Today, the majority of humanity lives in urban areas, which are significant sources of atmospheric emissions from human activity such as traffic, heating, industry, or power generation. Pollutants directly impact the local inhabitants’ health, but are also transported to neighbouring areas, undergo chemical evolution and can have an impact on climate. To understand and assess effective measures for reducing the effects, it is important to determine the source locations and strengths as well as relevant chemical processes. This has been the aim of the „Effect of Megacities on the Transport and Transformation of Pollutants on the Regional to Global Scales“ (EmerGe) project. Remote sensing methods allow fast and wide-spread probing of atmospheric trace gas distributions. Among them, Differential Optical Absorption Spectroscopy (DOAS) has come to play a prominent role due to its straightforward application. DOAS is widely used on the ground (good long-term observation, but poor spatial coverage) and on-board satellites (excellent global coverage but low spatio-temporal resolution). The gap between these two implementations can be covered by aircraft-based measurements with their high temporal and spatial coverage for the period of the flight. The Heidelberg Airborne Imaging DOAS Instrument (HAIDI) was designed to provide trace gas distributions of extremely high temporal and spatial resolution (e.g. 40 m x 40 m at 1.5 km flight altitude at 10 ms temporal resolution) in 2D and 3D during overflight. Within the EMerGe 1 project, HAIDI was installed on the research airplane HALO (High Altitude and LOng range research aircraft) of the DLR (German Aerospace Center). Within EMerGe 2 two missions (July 2017 in Europe and March 2018 in Asia) were performed to investigate the chemical composition of the outflow of megacities and the atmospheric impact of urban pollution. They constituted a major team effort of collaboration between a number of German research institutions and many foreign partners. Within this project, the column density distributions of the major air pollution constituents NO2, SO2, and HCHO were observed by HAIDI. In addition O4 column densities were derived and used as indicators for radiation transport. Target areas included Paris, London and the Po valley area as well as Manila, Taiwan cities and the outflow of pollution from mainland China. HAIDI possesses three independent scanning telescopes. Together, their observations contain additional information about the vertical distribution of the surveyed trace gases. The 3D distributions of trace gases were inferred by a newly developed inversion algorithms using data from a radiative transfer model.
