When Origin Energy permanently shuts down the furnaces at its Eraring power station in 2025, seven years earlier than expected, it will slash the amount of coal burned in New South Wales by around a quarter.
By then, the Liddell power station in the nearby Hunter Valley will have already closed, leaving just three coal plants remaining in the state.
What will it mean for air quality once they are gone?
Experts say while the state's air quality is good by world standards, every power station closure will bring health benefits – not only for the area the power stations are located, but for Greater Sydney.
Reduction in premature deaths
One of the deadliest pollutants from coal power stations is fine particulate matter, or PM2.5, which is known to increase the risk of heart attacks, strokes, cancer, and respiratory illnesses.
A NSW and CISRO study in 2020 found wood heaters, motor vehicles, and power stations are responsible for more than half of emissions from man-made sources.
The study estimated long-term exposure to fine particle pollution caused 420 premature deaths in the state each year, attributing 45 of those to coal-fired power stations.
"Having Eraring shut down will reduce those 45 deaths by at least a quarter, possibly more," said GP and University of Newcastle academic Ben Ewald.
"That's because the prevailing wind direction does tend to blow down to Sydney where more people live, so it has a larger impact.
Pollution not only causes deaths but also leads to poor health and quality of life outcomes, according to Sydney University environmental epidemiologist Geoff Morgan who was involved in the study.
"We estimated that air pollution is responsible for around 6,000 years of life lost," he said.
"Put another way, if taken as an average, it means everyone loses 50 days of life.
"And around 10 per cent of that could be attributed to the air pollution from the power stations."
Affect on childhood asthma
Nitrogen oxides (NOx) are pollutants known to exacerbate respiratory illness and increase asthma attacks, particularly in children.
Exhaust from motor vehicles is the largest source of NOx in Sydney, while in Newcastle it is shipping and in Wollongong it is industry.
But power stations are the biggest contributors in the regional areas where they are located.
Guy Marks, a respiratory physician and epidemiologist from the University of NSW, said asthma had many causes, but such a reduction from Eraring's closure was not immaterial.
"It is likely that a reduction in emissions from the Eraring power station will reduce exposure to pollutants, including nitrogen dioxide, and that is likely to have a broad range of beneficial effects on health."
A study last year by Dr Ewald and Professor Marks found a 25 per cent reduction in NOx concentrations would avert between 2,500 and 12,000 cases of childhood asthma each year in NSW.
As air pollution and its impacts on health decrease, so too will the health burden on the public purse.
A NSW government-led study last year estimated the current health cost of particle pollution from coal-fired power stations at a "conservative" $4.40 per megawatt-hour of energy produced.
That puts the health bill in NSW last year at around $236 million.
It won't be overnight
Just as adverse health effects of pollution tend to accumulate over your lifetime, the main benefits will also take time to emerge as levels decrease.
But the health of newborn babies, Dr Ewald said, could be one early indicator.
"Foetal growth is slowed down in air with fine particle pollution, so we should have healthier babies within nine months of turning off the power station.
But Luke Knibbs from the University of Sydney said more sources of emissions need to be addressed before there is a discernible impact on health.
"While it's tempting to assume this will have immediate local and regional health benefits, it's important to consider that there are many other strong sources of those pollutants, in the Hunter area especially," he said.
"The health impact of shutting one facility, while laudable, is likely to be quite modest.
"Hypothetically, if emissions from all coal-fired plants dropped to zero overnight, there's good evidence from Australian studies that such changes would lead to tangible health benefits over time."
The Australian Energy Council, which represents power stations, said air pollution had many sources and attempts to attribute direct health impacts to particular sources carried "a high risk of error".
