Estimating NO_x emissions of stack plumes using a high-resolution atmospheric chemistry model and satellite-derived NO₂ columns

Abstract. This work contributes to an European Monitoring and Verification Support (MVS) capacity for anthropogenic CO₂ emissions. Future satellite instruments that map CO₂ and NO₂ from space will focus on hot-spot emissions from cities and large point sources, where CO₂ emissions are accompanied by emissions of NO_x. To use NO_x as proxy CO₂ emission, information about its atmospheric lifetime and the fraction of NO_x present as NO₂ is required to interpret NO₂ plumes. This paper presents Large Eddy Simulations with atmospheric chemistry of four large point sources world-wide. We find that the chemical evolution of the plumes depends strongly on the amount of NO_x that is emitted, next to wind speed and direction. For large NO_x emissions the chemistry is pushed in a high-NO_x chemical regime over a length of almost 100 km downwind of the stack location. Other plumes with lower NO_x emissions show a fast transition to an intermediate NO_x chemical regime, with short NO_x lifetimes. Simulated NO₂ columns mostly agree within 20 % with the TROPOspheric Monitoring Instrument (TROPOMI), signalling that the emissions used in the model were approximately correct. However, variability in the simulations is large, making a one-to-one comparison difficult. We find that wind speed variations should be accounted for in emission estimation methods. Moreover, results indicate that common assumptions about the NO₂ lifetime (≈4 hours) and NO_x: NO₂ ratios (≈1.3) in simplified methods that estimate emissions from NO₂ satellite data (e.g. Beirle et al., 2019) need revision.