Measuring air quality is inherently a measure of excess—any amount of toxic nitrogen oxides, ground-level ozone, and fine particulate matter is probably bad for human health. But when it comes to federal regulations, the notion of excess gets a bit wonky. When a refinery or plant outstrips the limits set by the local public health authorities to cap pollution, those fumes are considered “excess emissions,” or, more wonkily still, “exceedances.”
Emissions limits are arbitrary, of course. Less pollution is always better in a country where more than 20 people die every hour from poor air quality, and where that burden skews toward communities of color. But parsing the human cost of these overflows is helpful for weighing—or possibly tightening—those arbitrary limits. So Nikolaos Zirogiannis, an environmental economist at Indiana University, decided to quantify the health toll in one state: How many people die each year as a result of that extra pollution?
His team chose to focus on Texas, where the large number of fossil fuel and chemical plants combines with the state’s industry-friendly regulations to make it a hot spot for excess emissions. But it also happens to have the nation’s strictest public disclosure requirements; in 2001, state lawmakers mandated not only that facilities must report excess emissions within 24 hours, but that this data be updated daily for public review. “Texas is the only state in the country that has a very, very detailed record-keeping requirement in place for those types of emissions,” Zirogiannis says.
He and his team combed through 15 years’ worth of reports, as well as mortality statistics and data from local air quality monitors. They concluded that every year, 35 elderly people die in Texas as a result of those excess emissions—in other words, these are deaths that would not have happened had all polluters kept within their permitted limits. It’s the first time any scientists have linked health effects to this subset of pollution. The results will appear in the July issue of the Journal of Environmental Economics and Management.
“This is a very high number,” says Zirogiannis, “because it’s a number that’s coming only from those exceedances.”
The main way the team linked these emissions to deaths was by isolating the degree to which they boost local levels of ground-level ozone, a nasty pollutant that can trigger heart problems and respiratory disease flare-ups. “There’s a huge body of literature linking elevated levels of ozone to respiratory and cardiovascular mortality,” says Joan Casey, an environmental health scientist at Columbia University who was not involved in the study. Heart attacks, strokes, asthma attacks, the exacerbation of chronic obstructive pulmonary disease—“those are the types of outcomes that I would expect are accounting for what they’re seeing here,” Casey says.
Oil refineries, natural gas facilities, chemical plants, power plants, and pipelines are hardly closed systems. Every time one shuts down for maintenance, starts back up, or just happens to malfunction—that’s an opportunity for unusual emissions. Nitrogen oxides, carbon monoxide, volatile organic compounds (VOCs), or other pollutants spill into local air. Each can be hazardous on its own, but in a sunlit atmosphere, these chemicals also contribute to the formation of ground-level ozone.
The team made the link between industrial air pollution and spikes in local ozone levels by collecting reports from the Texas Commission on Environmental Quality for the years between 2002 and 2017. This data showed when, where, and why releases were made, and what kind of chemical pollution was involved. They found a correlation between the release of nitrogen oxides, carbon monoxide, and VOCs with jumps in the ozone readings from monitors tracked by the Environmental Protection Agency.
The question then was whether these local spikes in ozone also tracked with an unexplained increase in deaths among people who lived nearby. So, next, the team pulled 15 years of CDC data on cardiovascular and respiratory mortality rates for Texas, broken up by county and month. For most age groups, they found no significant evidence that the number of deaths increased when local facilities had excess emissions. But for the elderly, especially those above age 85, Zirogiannis says their analysis proves the link is direct—these excess emissions cause dozens of deaths per year in Texas.
Their decade and a half of data across all Texas counties made it easy to identify which places and time periods showed unusually high levels of both ozone and deaths. (Since ozone is best known for causing heart and lung issues, they only focused on those causes of deaths.) Overall, they concluded that a 10 percent monthly boost in regional ozone levels increased the rate of death among the elderly by 3.9 percent.
The cause of those deaths, the team concluded, is contained within the 52,335 emissions reports they pulled—41,452 of which were about unplanned emissions, ones not resulting from scheduled startups, shutdowns, or maintenance. For example, a power disruption at a chemical plant on January 1, 2015, released over 15,000 pounds of the VOC ethylene into the air in just 45 minutes; the permitted limit for this emission was zero. Industrial ethylene has been shown to be one of the biggest contributors to ozone in Houston. In fact, the team found there are about 800 pounds of excess VOCs emitted near air quality monitors on an average day in Texas.
Zirogiannis and his team conducted their research following a tumultuous time in US air-quality regulatory history.
Excess emissions violate the 1970 Clean Air Act, the landmark federal law that authorized the EPA to enforce standards for ambient air quality. Private citizens technically have the power to bring civil suits against companies that violate the Clean Air Act. But it’s mostly up to states to monitor and enforce the rules. And industrial polluters have a mechanism they can use to avoid penalties: It’s called “affirmative defense.” They can claim a release of fumes was unavoidable, which under state jurisdiction may exempt those releases from being considered violations. Texas law allows companies to shield themselves this way. “So no civilians, no NGOs, can press charges against those companies in state court,” says Zirogiannis.
In 2011 the environmental nonprofit Sierra Club filed a petition with the EPA to outlaw such loopholes. By 2015 the federal agency called these state affirmative defense policies “substantially inadequate” to maintain clean air standards and requested that states remove their affirmative defense provisions. A handful of companies challenged the EPA in court for years, so judges put the EPA’s request on ice. In 2019 and 2020, under the Trump administration, the EPA withdrew its 2015 proposed rule and backed down from fighting against affirmative defense. “There’s been a long regulatory debate on how those excess emissions must be handled,” Zirogiannis says.
His interest in the health effects of emissions stems from his childhood in Athens, one of the most polluted cities in Europe. “I grew up as a child having asthma. So I have some understanding of what it means to grow up in an urban setting, in a highly polluted area, and suffering from a respiratory illness,” says Zirogiannis. “I can only imagine what people in those [Texas] areas go through when they are literally surrounded by those industrial facilities.” Unpacking the consequences this slice of pollution has on health, his team feels, is a way of forcing policymakers to reckon with the human costs of air quality regulation.
Their study confirms what environmental researchers and advocates have long known—bad air is bad for you. But experts not involved in the study say quantifying the health effects of these incidents shows that they’re more significant than previously thought. “We often need hard numbers to put in front of policymakers,” says Casey. “I was really excited that someone looked at this topic, because I do think these excess emissions are a big deal.”
“Every piece of evidence that we can compile to show why the policies we have are needed—and also need to be strengthened—is worthwhile,” agrees Bakeyah Nelson, the executive director of Air Alliance Houston, an environmental advocacy nonprofit not involved in this report.
That said, Nelson continues, “these emissions are also industry-reported. It’s likely an underestimate of what’s really happening.”
“I would say that our estimate is probably a conservative estimate,” Zirogiannis agrees.
And Casey points out that it’s very tricky to try to put a specific number on how many deaths excess emissions have caused. The data the team used tracked deaths by county and month, but specific home addresses and dates could make a correlation even stronger—or could contradict it. Still, she says, this data set is the best available, and Zirogiannis’ team filtered out confounding factors, such as hurricanes that would have caused both plant interruptions and deaths. “They did as well as they possibly could with the data they had,” Casey says.
While Zirogiannis believes these types of exceedances contribute to deaths nationwide, his team has struggled to carry out the same analysis outside of Texas. Other states don’t collect and disclose emissions reports the way Texas does. “That’s exactly the point we’re making,” Zirogiannis says. “We have no idea of what happens in other states.”
Zirogiannis is now recruiting people to use PurpleAir monitors at home in cities with a lot of industrial emissions, such as Houston and Indianapolis. Community participants would stick these $250 grapefruit-sized monitors outside their homes, and internal sensors would detect fine particles (not ozone) in real time. Those sensors would connect to the company’s online air quality map. That would help expand air measurements beyond what the government can collect on its own, and perhaps track evidence of neighborhood-by-neighborhood disparities. Zirogiannis says they are specifically prioritizing people living in minority and low-income neighborhoods.
Could having more monitors help shape local policy? “The short answer is yes,” says Nelson, because it would “document what many communities already know in terms of their air quality. Then they would be able to use that information to advocate for action to be taken.”
Data won’t influence policymakers just because it exists. “But in the absence of data,” she continues, “it makes it much harder to get those same people to act.”
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