In chemical transport models, NO_x emitted by lightning (LNO_x) is instantaneously diluted into the grid. A plume-in-grid parameterization to account for the sub-grid chemistry of LNO_x is presented. This approach was implemented into the GEOS-Chem model and leads to a relative increase of NO_x and O₃ (18 % and 2 %, respectively, in July) on a large scale downwind of lightning emissions and a relative decrease (25 % and 8 %, respectively, over central Africa in July) over the regions of emissions.