Time dependence of parameters within concentration model

The formulas used for the computation of the concentration in ConcentrationModel actually assume that all parameters are constant (virus removal rate and emission rate, in particular), but the implementation suggests that time-dependence of these could also be handled with the same formulas, which is not true:

        IVRR = self.infectious_virus_removal_rate(time)
        V = self.room.volume

        t_last_state_change = self.last_state_change(time)
        concentration_at_last_state_change = self.concentration(t_last_state_change)

        delta_time = time - t_last_state_change
        fac = np.exp(-IVRR * delta_time)
        concentration_limit = (self.infected.emission_rate(time)) / (IVRR * V)

One should use a single time (t_last_state_change, maybe) when getting IVRR and concentration_limit, or check that these do not change in-between two transition times.