There are calls for the New South Wales Government to suspend its assessment of a proposed fourth coal terminal for Newcastle, because pollution in the city already exceeds national standards.

The Coal Terminal Action Group (CTAG) monitored pollution levels for three days last month as 70 empty and loaded coal trains passed through the Newcastle suburbs of Beresfield, Sandgate and Mayfield.

The group's Coal Train Pollution Signature Study found particle pollution levels from the coal wagons were much higher compared to those from passenger and freight trains.

CTAG spokesman James Whelan says levels from coal trains also persisted for much longer, for up to four minutes after each train had passed.

"In some instances, particle pollution levels went up 120 per cent. That's a 13 times increase ," Dr Whelan said.

"Significantly, we found that unloaded coal trains can cause more pollution than loaded coal trains."

Dr Whelan says there is now sufficient evidence for coal wagons, empty or loaded, to be covered.

He has called on the State Government to legislate to force the industry to cover all wagons.

Last week, a Senate inquiry into air quality impacts on health also recommended covering coal wagons.

CTAG also wants the State Government to suspend the assessment of a proposed fourth coal terminal for Newcastle and ensure there is an independent assessment of the health impacts of particle pollution.

The group, which represents 21 community and environment groups, says the study was crowd-funded by more than 100 donors, making it the first of its kind in Australia.

"Never before has a community funded and conducted their own study with expert assistance," Dr Whelan said.

"Newcastle is the world's largest coal port. We have grown tired of government and industry inaction.

"We took matters into our own hands. We funded and conducted our own science, now we're calling for policy."

This is CTAG's second pollution monitoring study.

The first study found that the national standard for particle pollution was exceeded at seven locations. At some locations, levels more than 50 per cent higher than the national standard were recorded.

The results of this latest CTAG study are even more alarming.

The health effects of rail coal dust in the Hunter Valley have long been debated.

"There is no safe level of these kinds of particulates," according to Associate Professor Nick Higginbothom, from the Public Health Group at the University of Newcastle.

Associate Professor Higginbothom was part of the team who helped prepared and analyse the report.

He has warned of major health problems for entire populations exposed to elevated levels of coal dust pollution, including cardiovascular disease, impaired lung function and stroke.

"What we are most worried about of course is not just what is happening right now but the doubling and perhaps tripling of the movements of these trains in the future as the coal loader expands, " he said.

The mining industry says the CTAG study contains nothing new.

"This is an admirable attempt at contributing to the debate but this confirms what we already know," said Katie Brassil from Centennial Coal.

Ms Brassil says all trains generate dust and there is no evidence to support any of the study's recommendations.

"We've done a lot of monitoring and a lot of research in the area and we know that 86 per cent of the particulates in the air is actually not attributable to coal," she said.

Ms Brassil says there is nothing in the study to suggest that national health standards have been exceeded during the study.

"The report doesn't quantify or qualify the source of the dust. There's no evidence to suggest that covering coal trains is warranted," she said.

The state's Environment Protection Authority has welcomed the CTAG study.

EPA chairman and chief executive Barry Buffier says they would like to look at the findings in more detail.

He says the EPA is continuing to look at the issue of coal train dust and emissions from trains transporting coal.