Data points show the results of a series of forward simulations, in which the input conditions of the simulation (the total US anthropogenic emissions of all species) are reduced, joined by a cubic spline fit. The ‘average sensitivity’ lines indicate the gradient implied when impacts due to all sectors combined are calculated—that is, when the effects of atmospheric nonlinearity are taken into account—and thus the total results are scaled to match this. The ‘marginal sensitivity’ lines indicate the gradient of the response obtained by our GEOS-Chem adjoint simulation, and are used for calculations of individual sector and species impacts (where individual perturbations are of smaller size). The difference between the zero intercept of the two lines constitutes the ‘interaction’ effect. All values are population-weighted means for 2011.