Spatially and temporally resolved measurements of NO<sub><i>x</i></sub> fluxes by airborne eddy covariance over Greater London

Abstract. Flux measurements of nitrogen oxides (NOx) were made over London using airborne eddy covariance from a low-flying aircraft. Seven low-altitude flights conducted Greater London, performing multiple overpasses across the city during eight days in July 2014. NOx fluxes region (GLR) exhibited high heterogeneity and strong diurnal variability, with central areas responsible for highest emission rates (20–30 mg m?2 h?1). Other high-emission included M25 orbital motorway. The complexity London's characteristics makes it challenging to pinpoint single emissions sources definitively measurements. Multiple sources, including road transport residential, commercial industrial combustion are all likely contribute measured fluxes. Measured flux estimates compared scaled National Atmospheric Emissions Inventory (NAEI) estimates, accounting monthly, daily hourly variability. Significant differences found between flux-driven NAEI values up 2 times higher Central than those predicted by inventory. To overcome limitations national inventory contextualise fluxes, we used physics-guided data fusion train environmental response functions (ERFs) drivers (meteorological surface). aim was generate time-of-day surfaces calculated ERF relationships entire GLR; 98 % spatial coverage achieved GLR at 400 m2 resolution. All flight leg projections showed substantial domain, emanating major infrastructure. structure also investigated, through ERF, morning rush hour distinguished lower early afternoon. Overall, integration an ERF-driven strategy enabled first independent generation surface emissions, resolution eddy-covariance approach, region.