Radial H₂O number density in the coma of 29P after an outburst releasing icy grains during two days at a rate Q_dust. The results are shown for an elapsed time ∆T_outburst = 3 days from the onset of the outburst (plain symbols, leftmost curves) and ∆T_outburst = 25 days (open symbols, rightmost curves). Q_dust (given in the legend) is set so that the number of molecules within the HIFI beam (whose projected radius is ~8 × 10⁴ km) is 10³³ molecules at time ∆T_outburst = 3 days, corresponding to the 19.05 April 2010 measurement. The results for a_min = 3 and 8 μm are shown in red and dark red, respectively. The maximum grain radius is a_max = 50 μm, and the size index is α = −3.5. Results are shown for both ice-poor (v_i = 0.5) and ice-rich (v_i = 0.1) carbon grains. The dot-dashed line is a Haser model with Q(H₂O) = 4.6 × 10²⁷ s⁻¹ and expansion velocity .