Upper Hunter residents have threatened legal action over the NSW Government's failure to do a public health study into the effects of power station emissions and coalmining.

Some residents want a similar study in Lake Macquarie, with high levels of pollution coming from Eraring and Vales Point coal-fired power stations and the nearby Munmorah plant.

National Pollutant Inventory documents show that 45 million kilograms of nitrogen oxides (NOx) were emitted from Eraring power station, in south-west Lake Macquarie, in 2007-08.

In Muswellbrook, 49 million kilograms of NOx were produced from electricity generation.

Health authorities say breathing low levels of nitrogen oxides can irritate eyes, nose, throat and lungs.

Government documents show that power stations built before 2005 are allowed to emit NOx at much higher levels than those built after that date.

The NSW Government approved an upgrade to Eraring Power Station last year and, in doing so, allowed it to breach its own laws, the Clean Air Regulation 2002, for NOx.

Lake Macquarie MP Greg Piper said the Government must ensure that emissions from the state-owned power stations met modern health standards.

"We need to be continually adjusting the bar, if there's capacity to do it," Mr Piper said.

University of Newcastle academic Howard Bridgman said power stations had the advantage of tall emission stacks.

"Emissions only come down toward the ground in the Lake area in certain weather conditions," Associate Professor Bridgman said.

"My impression is the frequency of those periods is small."

A Department of Environment and Climate Change spokeswoman said the National Environment Protection Council sets national health-based standards for air pollutants.

The standards were under review, she said.