The largest research aircraft in the French fleet (SAFIRE brochure: https://www.umr-cnrm.fr/IMG/pdf/safireenglish.pdf ; SAFIRE web page: https://safire.fr ) is the ATR 42 that can carry 2000 kg of scientific equipment at 100 m s-1 for about 3.5 hours . We anticipate outfitting it with many instruments and minimal operators to make observations needed to address ACROSS scientific questions.
The general observational strategy with the aircraft in ACROSS is to observe the spatial and temporal abundance of key species related to the formation of ozone, SOA, and other secondary chemical products. This will likely involve flight patterns like those used in MEGAPOLI and other urban studies. The urban plume will be sampled by transects approximately perpendicular to the plume direction of flow. These will be performed at various distances and altitudes both upwind and downwind of the urban region and in areas of active biogenic emissions. Sampling plumes that intersect the location of the tower platform are of highest priority, although studying plumes outflow in other directions (including those not impacted significantly by biogenic emissions) will also be interesting and valuable. Also, sampling of air masses without urban influence in the region of the tower will contribute to assessing the chemistry of the biogenic emissions having less anthropogenic impact.
The instrument payload for the aircraft platform is still under development, but the table below shows its current makeup.
Tentative flight plans have been developed designed to measure mixtures of urban and biogenic air for various wind directions, with the plan to the east of Paris likely mostly urban. These plans are currently being evaluated and may change during the approval process. The colored circles show various waypoints during the flights, which are conducted mostly at low altitude (about 300 m above ground), but profiling at the locations marked by yellow triangles has been requested and is currently being evaluated.