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The object W33 is a giant molecular cloud that contains star forming regionsat various evolutionary stages from quiescent clumps to developed H II regions.Since its star forming regions are located at the same distance and the primarymaterial of the birth clouds is probably similar, we conducted a comparativechemical study to trace the chemical footprint of the different phases ofevolution. We observed six clumps in W33 with the Atacama Pathfinder Experiment(APEX) telescope at 280 GHz and the Submillimeter Array (SMA) at 230 GHz. Wedetected 27 transitions of 10 different molecules in the APEX data and 52transitions of 16 different molecules in the SMA data. The chemistry on scaleslarger than $\sim$0.2 pc, which are traced by the APEX data, becomes morecomplex and diverse the more evolved the star forming region is. On smallerscales traced by the SMA data, the chemical complexity and diversity increaseup to the hot core stage. In the H II region phase, the SMA spectra resemblethe spectra of the protostellar phase. Either these more complex molecules aredestroyed or their emission is not compact enough to be detected with the SMA.Synthetic spectra modelling of the H$_{2}$CO transitions, as detected with theAPEX telescope, shows that both a warm and a cold component are needed toobtain a good fit to the emission for all sources except for W33 Main1. Thetemperatures and column densities of the two components increase during theevolution of the star forming regions. The integrated intensity ratiosN$_{2}$H$^{+}$(3$-$2)/CS(6$-$5) andN$_{2}$H$^{+}$(3$-$2)/H$_{2}$CO(4$_{2,2}$$-$3$_{2,1}$) show clear trends as afunction of evolutionary stage, luminosity, luminosity-to-mass ratio, andH$_{2}$ peak column density of the clumps and might be usable as chemicalclocks.

Diversity of chemistry and excitation conditions in the high-mass star forming complex W33