The environmental lawyers group said on Sunday its inquiries revealed alarming errors in under-reporting from the state’s five large coal-fired power stations, including Eraring.

It followed claims Muswellbrook’s Bayswater power station used partial monitoring of its units to manipulate pollution estimates, prompting the environmental watchdog to investigate all plants in NSW. Bayswater was only required to report pollution from one of its four generation units and staff were instructed to supply lower sulphur coal to the unit being monitored, while dirtier coal was burnt in the other three, according to participants at a public meeting held with current owners AGL in March. AGL did not deny the station, which it bought from state-run Macquarie Generation in 2014, deliberately blended coal to mask the true emissions. It said it could not comment on operations prior to its takeover but had since introduced monitoring of all four units.

On Sunday, Environmental Justice Australia said its investigations showed the Mt Piper, Eraring and Vales Point power stations reported fine particle emissions had dropped 92 per cent, 60 per cent and 37 per cent respectively in just one year, despite generating more electricity. It said none of the power stations had installed the kind of emissions controls that would achieve this, none monitored their emissions 24/7 and all self-reported pollution data.

“These power stations appear to be dramatically under-reporting their toxic emissions,” Environmental Justice Australia researcher Dr James Whelan said.

“Without an accurate picture of the toxic pollution emitted by power stations, communities nearby don’t know what they’re breathing.”

Dr Whelan said independent continuous monitoring was needed.

Origin Energy, which bought the Eraring power station in 2013 from the government, said it "does not currently blend coal for use in the generating units at Eraring", according to a spokesman.

"All four generating units at Eraring are monitored annually consistent with the power station's licence conditions and emissions monitoring data is published on the Origin website and in annual sustainability reporting."

A spokesperson for the NSW Environment Protection Authority said a Commonwealth review of the National Pollution Invetory had commenced. The review would focus on identifying whether the right substances were being reported, the most valuable information was being collected and whether its collection was cost effective.

“The EPA is currently looking at the allegations power stations may not be accurately reporting their emissions,” the spokesperson said. “We will respond as appropriate.”