The NSW government changed adverse findings of a report on coal train pollution to suit its political goals, a community action group says.

Five months after emissions monitoring ceased and only six days before it was released, the report on dust from Newcastle coal trains was altered contradicting initial findings that "coal trains are much more polluting", the Coal Terminal Action Group says.

Spokesman James Whelan says 15 of the 18 findings in the Australian Rail Track Corporation's (ARTC) Particulate Emissions from Coal Trains report had been changed.