where the positive x-axis is aligned with the downwind direction, q is the mass of methane contained in puff p, σ y,z are dispersion coefficients discussed in Appendix A, and u is the wind speed at the time the puff was emitted. Note that while the wind vector is constant for a single puff, it is allowed to change between puffs, which is how the model accounts for variable wind conditions. The overall concentration profile is the sum of concentrations from each puff, and is given by