Ah, the soporific heat of the wood stove or the coziness of a fireplace. But these comforts come with a drawback: smoke and soot. And a recent study by a nonprofit research and advocacy group says that Worcester County experiences the worst of it.

“It’s crazy high, it’s so high, I was amazed when I saw that,” said Mary S. Booth, founder and director of the Partnership for Policy Integrity, on the organization’s finding that Worcester County had more air pollution from residential wood burning than any other county in New England. It was the eighth highest county in the country, in fact, according to the analysis of the Environmental Protection Agency’s National Emissions Inventory data.

But government agencies tasked with monitoring air pollution, as well as wood-stove industry representatives, highlighted that the data are based on estimates from census data on wood burning, not on emissions measurements. The latter show that Worcester County and all of Massachusetts meet annual and 24-hour standards for PM2.5 (particle matter less than 2.5 micrometers in diameter) the fine particle pollution of most concern in wood smoke.

“The real issue for us is, is there an actual air-quality problem based on these emissions, and the answer to that is no,” said Glenn Keith, deputy director in the Division of Air and Climate Programs at the Massachusetts Department of Environmental Protection. Mr. Keith said that road dust from paved and unpaved roads contributes more PM2.5 emissions than residential wood burning, according to the data. “We do have a statewide network of air-monitoring stations and we measure PM2.5 in the air and then we compare it to the EPA National Ambient Air Quality Standards for PM2.5. And we do attain all the standards.”

The EPA said that on a per-capita basis, all counties in Maine, Vermont and New Hampshire but one have higher residential wood-burning emissions than Worcester County. On a per-square-mile basis, Worcester County “no longer stands out” compared with other counties in New England, according to the EPA.

“We note that the map of PM2.5 from residential wood combustion produced by the Partnership for Policy Integrity is consistent with the 2014 National Emissions Inventory data,” EPA Spokesman Emily Bender said in a statement last week. “However, by displaying tons of PM2.5 from residential wood burning for each county, the map gives the impression that larger counties are more impacted by wood smoke than smaller counties.”

So what’s going on?

As so often happens in science, those interviewed shared different interpretations of the data and assigned it different importance.

The debate over the data mirrors the larger debate over whether wood is a clean and renewable fuel warranting state incentives. That debate is becoming more urgent due to the Baker administration’s plans to designate woody biomass - wood chips and pellets made from tree trunks, branches, sawdust and other plant matter - as a form of renewable energy.

Meanwhile, all sides agreed that air pollution from wood burning is important and are undertaking various initiatives to ensure that this pollution continues to decline.

The data

PFPI mapped the most recent data available from the EPA’s National Emission Inventory on PM2.5 emissions from wood heating, which includes wood-burning stoves, fireplaces, and furnaces, including outdoor wood boilers.

MassDEP notes that PM2.5 can penetrate deeply into the lungs and accumulate in the respiratory system. Scientific studies have definitively connected fine particles with asthma and chronic bronchitis, coughing, shortness of breath, heart attacks and premature death in people with heart or lung disease.

The data indicate that Worcester County had the greatest county-level emissions in New England and New York from residential wood burning, with 1,898 tons of PM2.5 released into the air in 2014. This was the eighth highest in the country. PFPI also analyzed the relative contribution of biomass combustion to PM2.5 emissions in Massachusetts and surrounding states. It found that wood burning is overwhelmingly the largest source of PM2.5 emissions from heating, ranging from 82 percent to 98 percent of the heating emissions per state. In Massachusetts, wood burning accounted for 83 percent of all PM2.5 emissions from heating and a quarter of the state’s total PM2.5 emissions.

But all interviewed noted the data were estimates, not measurements of actual emissions.

“It’s just a matter of working with the data,” said John Crouch, director of public affairs for the Hearth, Patio & Barbecue Association. “It’s a series of assumptions about how much wood is burned. I’m not saying they’re incorrect assumptions. But people look at a study like this and think there is somebody monitoring the wood smoke; it’s not, it’s a paper exercise.”

Mr. Keith agreed.

“All of this is based on estimates that EPA puts together based on census data,” said Mr. Keith. “They make certain assumptions to how much smoke a fireplace or a wood stove would emit, and they put it all together to come up with these emissions factors estimates, and estimates of activity of wood burning, and then they calculate the emissions …

“I think the reason that Worcester County has more emissions from the residential wood combustion sector than other counties is based primarily on its population and the degree to which Worcester County has rural populations versus urban,” Mr. Keith continued.

He and other government representatives pointed to emissions measurements as a more accurate way to measure PM2.5 pollution.

And looking at that data, neither the county nor state currently exceed standards for PM2.5 - which is a concentration of 12 micrograms per cubic meter annually or 35 ug/m3 in a 24-hour period.

The EPA acknowledged “isolated valley areas” in New England exceed the standard during short periods of time in the winter due to wood smoke. And the actual measurements show that Worcester on six occasions last heating season exceeded the PM2.5 standard in a 24-hour period. In comparison, however, Pittsfield had 17 occasions exceeding the 24-hour standard in September through March, according to raw data from MassDEP.

But Ms. Booth said that to measure attainment levels, scientists measure the concentration of air pollution not the tonnage emitted. The two are not directly comparable, she said.

“The EPA data are what they are ... EPA wouldn’t be spending tens of millions of dollars collecting these data and putting them online if they were worthless.” Ms. Booth said. “Of course they are going to downplay the problem, because it would make them look like they aren’t addressing the problem, which they aren’t.”

Addressing pollution, debate on clean energy

But the government and industry and environmentalists all said they are addressing wood-burning pollution, albeit by different methods.

Ms. Booth and other environmentalists attended a public hearing Monday to protest the Baker administration’s proposal that biomass become eligible for clean energy credits through the state’s Alternative Energy Portfolio Standard.

Proponents consider biomass a renewable fuel as long as the burned trees are regrown according to sustainable forestry practices, and say it thus provides a more green alternative to fossil fuels such as oil and coal.

“The (Massachusetts) forest is growing about six times as fast as it’s dying, falling down or being cut,” said Charles Thompson, president of the board of the Massachusetts Forest Alliance. “As long as the carbon accumulation (from growing forests) in an area exceeds the carbon that is going in the other direction, it is OK, because it offsets.”

Opponents such as Ms. Booth say that burning biomass is not carbon neutral, especially when taking into account the carbon cost of making and transporting wood products for burning. Burning wood also creates pollution in the form of PM2.5 and could lead to greater deforestation, opponents argue.

“Climate change is just so urgent, the need to reduce emissions is so urgent ... we need to grow trees, not cut them down and burn them,” Ms. Booth said. “We need to take carbon out of the air, and so liquidating trees and burning them does not do that.”

She advocated for incentivizing wind, geothermal and solar, not wood burning.

A spokesman for the Department of Energy Resources, the state agency charged with drafting the regulations, said in a statement that he could not comment on regulations that are in the ongoing rule-making process.

“The Baker-Polito administration remains committed to diversifying the commonwealth’s energy portfolio through a balanced approach, and looks forward to working through the regulatory process to ensure that the commonwealth both meets the demands of our ratepayers and reduces carbon emissions,” said DOER spokesman Kevin O’Shea.

But EPA said government and the industry are working together to reduce wood-smoke pollution, which all sides admitted had been generally decreasing over time.

A notable way that states and the American Lung Association are doing so is through wood-stove change-out programs, which offer financial incentives to replace an old wood-burning stove with a newer, more efficient model.

“The point is there’s a lot of old stoves in the area in Worcester and the surrounding towns,” said Rocco DiVerdi, owner of Enchanted Fireside on West Boylston Street in Worcester. His store offers incentives up to nearly $3,000, depending on income, for residents to switch out an old for a new stove. “We want to get the old stoves that are putting out a lot of particles into the air.”

The American Lung Association has run several change-out programs over the years, often as a result of settlements with polluters who have been fined by the EPA or other institutions.

“One of the things that is confusing in this whole thing, is people are tending to equate modern wood energy systems with the sort of stereotypic notion of old wood stoves, and they’re not the same thing at all,” Mr. Thompson said. “The advances in technology in both efficiency and emissions control over the past ten years are just remarkable.”

And Mr. Thompson noted that - whether arguing for or against biomass as a renewable fuel source - all sides agreed on one thing.

“If we can keep forests as forests, that’s really the ultimate goal here,” Mr. Thompson said.