I have done some deeper research. It seems that TSG2600 is for air quality measuring slightly better than TSG2602 - higher sensitivity for standard city outdoor air contaminants.
See basic classification at http://www.directindustry.com/prod/figaro-engineering/semiconductor-air-quality-sensors-29357-147448.html
info and links at http://lekernel.net/blog/2009/07/toxic-gas-sensors-at-tmplab/
Especially measuring results at http://lekernel.net/blog/2009/09/sanobot-data-for-the-first-half-of-september/
But TSG2602 detect VOCs - eg. leaks of dangerous gases from factory…
I ordered TSG2600 and MQ-135.
Once the parts arrive, I’ll try to compare them.
However, some donation for development would be nice. These sensors are not the cheapest.