Ground-Level Ozone

Car emissions (Photo credit: Simone Ramella/CC BY 2.0)

Oh No, Ozone! Under Construction

Game of Thr(Ozone) A Song of Respiratory Illness and Climate Change

Humankind has mixed feelings above ozone, and with good reason. Think of this pale blue gas as a long-distance lover who’s a bit too smothering in-person, or that one friend with the super clingy cousin.

On one hand, stratospheric ozone prevents most of the sun’s harmful ultraviolet (UV) rays from reaching us, essentially forming a shield of sunscreen 6 to 31 miles above the Earth’s surface. You might have remembered stratospheric ozone (or, more accurately, its concerning lack thereof) making headlines about 20 years ago, when a team of British scientists discovered of a huge hole in the ozone layer above Antarctica. Luckily for our skin and continued existence, the international community came together in response to phase out the use of chlorofluorocarbons (CFCs): synthetic chemicals used in aerosol sprays and refrigerants that break up ozone by “stealing” its oxygen atoms. Now, some scientists are predicting that by 2080, global ozone will recover to its 1950s levels—assuming greenhouse gas emissions don’t get in the way before then.

And that’s all good and well for the ozone layer, but now we’re the ones we might need to worry about surviving until then in one piece. Stratospheric ozone’s evil twin, tropospheric ozone, has become partners in crime with global climate change. Tropospheric ozone also goes by ground-level or ambient ozone, but no matter what you call it, it’s bad news for us. A key component of smog, tropospheric ozone is the lovechild of sunlight and some of our (least) favorite pollutants—namely, nitrogen oxides (NOx), carbon monoxide (CO) and volatile organic compounds (VOCs). VOCs refer to a compound of carbon, excluding some varieties, that participate in atmospheric photochemical reactions. And while there are some natural sources of these emissions—particularly VOCs, which are released by some plants in a form of self-defense against insects—we supply our own fair share through fossil fuel combustion and industrial processes. On rare occasions, stratospheric ozone itself will convert to the dark side, and contribute to ground-level ozone levels near the surface.

These ingredients are bad enough on their own, even if you’re one of those weird people that likes the smell of gasoline. NOx is one multitasking molecule; besides contributing to ozone, it’s also a big component of acid rain and destroys good stratospheric ozone. Not to mention, both NOx and VOCs exacerbate respiratory conditions on their own. Add a little sun to the mix, and the solar energy separates the nitrogen oxide from one of its oxygen molecules. Desperate for companionship, the lone oxygen will quickly bind with one of our friends, O2 (breathable oxygen), to create one of our enemies: ground-level ozone (O3). Who needs soap operas when you’re keeping up with the drama of atmospheric chemical processes, right?

And in a cruel twist of fate, the more sun, the more tropospheric ozone. In other words, the days that you’re probably more likely to be outside (think higher temperatures, sunnier skies, and lighter winds) are characterized by same conditions that ground-level ozone thrives in, meaning you may want to rethink how much time you’re outside (although ground-level ozone has a nasty habit of getting inside, too). Plus, it’s not like you could try just avoiding this gas like you would a clingy cousin; it’s both odorless and colorless. Unfortunately, its effects on the human body are quite noticeable.

An Inside Job

That’s not to say that our bodies don’t have any defenses against outdoor air pollutants. Most of the time, your upper respiratory tract—including your larynx (which holds your voice box), pharynx (which connects your nose and mouth to your esophagus), and nose (you’re probably familiar with this organ)—are pretty good at “scrubbing” air pollutants out of the oxygen we breathe, purely because the relatively extensive, slimy surface area in there gives your body more chances to snag it.

Unfortunately, our respiratory systems aren’t really doing us any good when it comes to ground-level ozone. The “scrubbing” effect of the upper respiratory tract works best with water-soluble gasses like sulfur dioxide and chlorine gas and, you guessed it, ozone has very limited solubility in water. That means that the majority of inhaled ground-level ozone is able to infiltrate deep into the lower respiratory tract. Once there, the ozone dissolves in the thin layer of epithelial lining fluid (ELF) throughout the lungs: the very barrier designed to protect the airways from infection.

Here, deep in the lungs and several steps past the body’s best defenses, the ground-level ozone begins to unleash pure chaos as it targets the proteins and lipids on the surface of the cells in the lung lining fluid. The result is oxidation, where many of the body’s biomolecules are forced to take on an extra oxygen molecule after interacting with the invading ozone. Depending on the substrate, this chemical process either protects the underlying epithelium from interference, or, most frequently, does the exact opposite: creating highly reactive compounds such as lipid hydroperoxides, cholesterol ozonization products, ozonides, and aldehydes. In other words: bad guys. In response to this new threat, the body is forced to fall on the defensive, sending an army of white blood cells (leukocytes) and alveolar macrophages (or “dust cells,” which swallow any threats) to the front lines. This surge in activity is also known as inflammation, as the body orders leukocyte-rich blood to flood to the lungs.

In small doses, inflammation is an important and instinctive immune reaction. You might notice the distinctive train of blood as a warm, pink-red outline thinly encircling a healing wound. But if the lungs are continually exposed to stress, like ground-level ozone, and not given the chance to properly heal, the lining of the lungs can become irritated and chronically inflamed. Think of it as if you began to constantly skin the same knee in the same exact spot, day in and day out. Many experts compare the effects over time to something like a sunburn on the lungs—it’s the same story of continuous exposure, insufficient biological defense, cell damage, and increased health risks. And when it comes down to inhaled ozone exposure, the story doesn’t end very well for us: inflammation also causes your airways to constrict, making it much harder to inhale to total lung capacity.

In the best-case scenario, this leads to coughing, throat irritation, chest pain while breathing, and shortness of breath. But in the worst cases, ozone inhalation can aggravate existing lung conditions (asthma, emphysema, and chronic bronchitis), and increase the chance of lung infection and disease. In fact, being exposed to high levels of ozone can continue to permanently damage the lungs, even when symptoms have subsided. In adults, it can cause chronic obstructive pulmonary disease—a permanent side effect of ozone exposure that’s more commonly associated with cigarette smoking, which makes it increasingly hard to breathe as the airways narrow. In children, breathing ozone early on can lead to abnormal lung development—a health cost they’ll carry for the rest of their lives. Together, these health effects have serious and tangible consequences for society, from school absences, to medication use, doctor’s visits, emergency room admissions—and graveyards.

I don’t mean to be a downer, but it’s about to get worse. Take a deep breath—but maybe check the daily ozone levels first.

Climate Change’s Atmospheric Cocktail

Here’s the explanation in a nutshell: as climate change gets comfortable on Earth, rising greenhouse gas emissions also making our planet’s surface increasingly inviting for ozone to move in. So unless humankind wants to permanently room with lung inflammation and irritation, we’re going to have to kick out both, preferably as soon as humanly possible.

The long story actually starts off on a good note. Believe it or not, most people have realized over time that ground-level ozone does very little good for us (read: none whatsoever). Essentially, this means that ozone-creating emissions (or ozone “precursors”) from human-originating sources have been decreasing fairly steadily in the United States. Nitrogen oxide emissions have decreased by more than 60 percent between 1970 and 2016, no thanks at all to industrial processes, which are only rising. Instead, the reduction is mostly due to stricter environmental regulations that are hitting down hard on car emissions, including nitrogen oxides, as well as the other major ozone precursor, VOCs. In fact, national total estimated VOC emissions from anthropogenic sources (excluding natural wildfires) decreased by an impressive 47 percent between 1990 and 2011 (from 23.0 million tons to 12.3 million tons).

We wouldn’t start celebrating quite yet, though. Despite these decreasing emissions, climate change, which remains as inconvenient since Al Gore first pointed it out, encourages the development of meteorological conditions that are more favorable to ozone formation. In other words, climate change is doing its darndest to make sure that ground-level ozone levels continue to rise, with or without the support of human emissions. This means that reaching national air quality standards for ground-level ozone will be increasingly difficult as climate change offsets some of the improvements that would otherwise be made from reducing emissions. This effect is called the “climate penalty,” or otherwise known as, “Why life isn’t fair” or “Why climate change sucks.”

Sticking with the theme of injustice, it’s also becoming increasingly evident that climate change has a number of tricks up its sleeve when it comes to giving tropospheric ozone a helping hand. The main tool in its arsenal, unsurprisingly, is higher global temperature. Global temperatures have been accelerating upward in the past 30 years; 2001 to 2010 was the warmest temperature ever recorded in history. Already, average U.S. temperatures have increased more than two degrees Fahrenheit during the past century. Besides fanning heat waves, melting polar ice caps, and significantly altering delicate ecosystems (as if those aren’t bad enough in and of themselves), increased temperatures also aid in ground-level ozone formation by increasing the chemical rates at which ambient ozone develops. Basically, higher temperature makes molecules in the atmosphere less stable, so they’re more likely to separate, bounce around, collide, and ultimately end up combining into ozone.

And that’s not all, folks. Besides accelerating the chemical formation of ground-level ozone, higher temperatures can increase the emissions from anthropogenic and vegetative sources. Plants, for example, may create more emissions in a warmer world, since some of them are produced in response to heat stress. Not to mention, as the temperature increases, the warmer air, which is less dense, becomes capable of holding more water, and the percent of water in the air falls. In other words, relative humidity—the percent of water in the air relative to the amount of water the air can hold—drops. This reduces the main arsenal for cloud cover, promoting ozone formation. (Full disclosure: there’s been some argument over this. For a long time, the status quo was that relative humidity would stay constant as climate changed, because while warmer air can hold more water, increased temperature also means more evaporation, and thus more water in the atmosphere. A new analysis by NASA, however, has found that while more water will indeed evaporate as well as temperatures increase, it won’t be enough to keep relative humidity levels from falling a bit.)

And while climate change and higher temperatures are probably best known for speeding things up, in certain cases, they’re all about slowing down. Increasing temperatures are at least partly responsible for slowing global wind patterns. A comprehensive study by atmospheric scientists at Indiana University found that in most of the United States, wind speeds appear to be slowing down by more than 1 percent a year. The stagnant atmosphere will allow ozone and ozone precursors to stagnate and accumulate over time, choking unlucky regions—and not to mention, making it that much harder to get renewable wind energy off the ground and into our power grids.

Windmills love pressure differences (Photo credit: Leif Harboe/CC BY-NC-ND 2.0)

Here’s what’s happening on an atmospheric level: winds are driven by pressure gradients, because air flows from high pressure to low pressure settings. Think of the average college student, who also prefers resting in lower-pressure environments. The bigger the difference in pressure is, the larger the incentive for the student to get from study time to nap time as quickly as he or she possibly can. In our scenario with climate change, as the temperature increases, so does the air pressure. Imagine, for example, heating a container full of gas. As the temperature increases, the gas molecules inside have more energy and hit the container walls more often and with more force, increasing the pressure from the inside out. On a global scale, as the polar regions warm significantly more quickly than the tropics, the temperature difference between the two areas falls, slowing air circulation between them, and minimizing any breezy reprieve for areas plagued by ground-level ozone. In other words, if nap time was just as much pressure for a college student as study time—thanks to a noisy roommate, for example—they’re more likely to stay in the library. You’ve probably heard of global warming, but global stilling’s been avoiding the spotlight.

And ozone concentrations near the ground aren’t just influenced by horizontal wind patterns. They’re also strongly affected by the upward and downward movement of air (also known as “vertical mixing”). Normally, temperatures are warmer closer to the Earth’s surface than further from it. This fact makes intuitive sense—most people think of outer space to be pretty cold—but is also backed by science. As the sunlight warms the ground, the ground in turn warms the layer of atmosphere directly above it. Under certain conditions, however—like on calm, clear nights, when the Earth’s surface cools very quickly—the air near the ground becomes cooler than the air above it. This phenomenon is referred to as a temperature inversion, where a sandwich of warm air forms that acts like a lid on the Earth’s surface. It traps emitted air pollutants near the ground, preventing them from diluting or mixing in the atmosphere and deteriorating the air quality. There’s evidence that these kinds of high-pressure systems are both contributing to and exacerbated by climate change in some regions, like Greenland and the larger Arctic regionthe kind of vicious feedback loop that reminds us of how we got catapulted into climate change in the first place.

Location, Location, Location

That being said, when it comes to Atlanta, we’re happy to start with some good news. Ground-level ozone levels have decreased significantly since 1999, dropping from 120 parts per billion to the upper 70s. The scary thing is, nobody is sure if climate change will cooperate with Atlanta’s efforts to keep that trend going downhill. Despite the overall pattern of decline thanks to increasingly stringent regulation, spikes in tropospheric ozone aren’t exactly unheard of. In fact, the city has only been consistently decreasing in annual average ozone levels since 2012, and there’s one county in Georgia that has actually been on the rise. And that’s not the only ominous sign. Despite consistent ozone precursor emissions reductions, the sun-dependent ozone season is beginning to extend into the fall, peaking in October rather than July. Is climate change behind it? What’s its end game?

Unfortunately, climate change is fickle—basically, a fake friend (acquaintance? enemy? frenemy?) that acts completely differently depending on the setting it’s in. It’s one of the reasons why most scientists and organizations increasingly prefer referring to the global phenomenon as “climate change” rather than “global warming,” since increased surface temperatures is just one tick on a laundry list of symptoms that actually includes cooling in certain places—like snow in the Sahara Desert last December for the first time in decades.

What almost all research scientists can agree on right now is that the Southeastern United States, which includes Atlanta, Georgia, is a highly contested region when it comes to the effects of climate change on local tropospheric ozone levels. Here’s just a taste of that uncertainty: Hogrefe et al (2004) found an increase in projected summertime ozone concentrations in the 2050s but a decrease in the 2080s relative to the 1990s; then Racherla and Adams (2006) showed the Southeast to be the U.S. region with the largest ozone increase nationwide in response to the effects of climate change between 1990 and 2050. Murazaki and Hess (2006) also found fairly large ozone increases in the Southeast, while Wu et al (2008) found little effect at all, with some potential for a “climate benefit”—as in, climate change could actually help reduce ground-level ozone levels (more on this later). Lin et al (2001) discovered the chance of exceeding 85 parts per billion as an average daily maximum concentration increases with temperature across the U.S., although the increase in the Southeast is much weaker compared to the northeast.

In other words, nobody is 100 percent sure what climate change will do to ground-level ozone here in Atlanta.

That isn’t to say, however, that all these people have no idea what’s happening at all. Almost all studies studying ground-level ozone projections in the Southeastern U.S. found and incorporated climate-change driven increases in isoprene. Remember earlier, when we mentioned vegetative sources of ground-level ozone precursors? In fact, the largest source of VOCs by far is naturally emitted by vegetation, and is more often than not in the form of isoprene. This common organic compound is produced by many species of trees, including oaks, poplars, eucalyptus, and some legumes. Plants use isoprene to combat different stresses, particularly in response to moderate heat stress in order to protect against large fluctuations in leaf temperatures or destabilized cell membranes. As the world warms, it’s widely agreed that isoprene emissions will rise with surface temperatures, especially in forested regions like the Southeastern United States.

The debate starts when we try to determine what effect increased levels of isoprene will have on the formation of ground-level ozone. The problem, of course, is in the chemistry. You might remember when we talked through the basic chemical reactions behind ground-level ozone formation. To quickly recap, solar energy cleaves nitrogen oxide from one of its oxygen molecules, which then does a complete 180o turn to bind with breathable oxygen (O2) to ultimately create O3—ground-level ozone. This is still the main idea behind how carbon monoxide, NOx, and VOCs become pressured by sunlight to form tropospheric ozone. But in order to understand why increasing isoprene emissions have thwarted our attempts to predict the future of tropospheric ozone levels, we need to take a few chemical steps back in the ground-level ozone formation process.

The whole thing starts with the hydroxyl radical OH, a highly reactive and consequently short-lived marriage between oxygen and hydrogen. When OH bumps into carbon monoxide, or some kind of VOC (hint: like isoprene!), a new radical chemical compound forms, which immediately oxidizes in the presence of breathable oxygen (O2). This leads to the creation of carbon dioxide (CO2) and an intermediate peroxy radical, which we’ll refer to as RO2*. Now, here’s where things get a bit trickier. When RO2* inevitably reacts with nitrogen oxide (NO), one of two things can occur. In the first scenario, the chemical reaction leads to the formation of nitrogen dioxide NO2, which then loses an oxygen molecule to breathable oxygen thanks to the power of solar energy and ultimately creates a trio of notorious oxygen molecules better known as ground-level ozone.

But in the second story, RO2* and nitrogen oxide produce a stable organic nitrate that has nothing whatsoever to do with ozone and actually ends up taking some NOx out of the picture. In this case, increasing ground surface temperatures thanks to climate change, which ramp up isoprene emissions from heat-stressed trees, would actually end up reducing ground-level ozone emissions—that weird climate benefit we were talking about earlier. But even then, there’s still debate on how the story ultimately ends, because scientists are still trying to determine if isoprene nitrates represent a temporary or permanent sink for NOx. Either way, understanding the chemistry behind how isoprene interacts with ozone precursors sheds light on the range of predictions on future ground-level ozone trends in the Southeast. According to one estimate, if isoprene nitrate is treated as a terminal sink for NOx, ozone over the Southeastern U.S. will stay constant or even decline in the 2050s. On the other hand, if isoprene nitrate is allowed to recycle in the atmosphere and therefore contribute to ground-level ozone formation, ozone levels are predicted to increase by as much as 7 parts per billion in the same region.

So here’s the takeaway on how climate change will affect ground-level ozone formation in Atlanta: an incredibly unsatisfying, “We’re not sure.” We definitely have hope and encourage you to stay optimistic, considering recent declining annual trends in tropospheric ozone near the city. But between mixed interpretations of rising isoprene emissions, and not to mention shifts in wind patterns and pressure systems, precipitation and water vapor levels, wildfire incidents, and government priorities, all we can confidently say that we do know at this point is that we don’t entirely know how ozone levels are going to react going forward. Climate change, you win this round, but the fight is far from over.

On Ozone's Case Confronting Ozone in Atlanta

A Moving Regulatory Target

Not including climate change, ground-level ozone doesn’t have a lot of fans. In addition to the myriad of negative respiratory health effects this pollutant unleashes on the lungs, it also wreaks havoc on sensitive vegetation and ecosystems and contributes to smog. (Fun fact: one supporter that it did have was Claude Monet, the founder of French Impressionist painting. He loved documenting scenes of heavily-polluted London in the early 1900s and went so far as to claim that without the smog, “London would not be beautiful.” Coincidentally, the guy also died of lung cancer, so take that as you will.)

Considering all that negative press, it’s not surprising that many countries, regions, and states have taken steps to combat or minimize ground-level ozone formation. On American soil—or rather, air—ozone pollution is controlled through the Clean Air Act (CAA), a comprehensive federal law designed to control and regulate air pollution on a national level from both stationary and mobile sources. Among other things, the law requires the EPA to establish National Ambient Air Quality Standards (NAAQS) for six common air pollutants in the name of protecting public health and welfare. Ozone (O3) has the distinctive (dis)honor of being identified as one of these toxins, along with sulfur dioxide (SO2), particulate matter (PM), carbon monoxide (MO), lead (Pb), and nitrogen dioxide (NO2). Altogether, members of this troublesome squad are better known as “criteria air pollutants,” because the EPA deems that their levels in outdoor air need to be limited based on health criteria. We might be a little biased, but we can’t help but agree.

Once the EPA has determined a maximum allowed measurement level for ozone to be present in outdoor air, the agency works with states and tribes, reviews recent data from air quality monitors, and gathers other relevant technical information to size everybody up against the standard. Then, following Title I of the CAA, the EPA designates areas as either “attainment” or “nonattainment” with national ambient air quality standards, like ground-level ozone, within two years after the NAAQS are first issued. Attainment areas either meet, or in some cases go above and beyond (lookin’ at you, California) the national standard; nonattainment areas fail to meet the benchmark.

Once these attainment labels are agreed on, state and local governments and air quality management agencies have three years to develop State Implementation Plans (SIPs). The proposals detail a general strategy for attaining as well as maintaining standards in their region, and include a specific plan for reaching those standards for any areas that were designated as nonattainment. Generally, they include programs like air quality monitoring, air quality modeling, emissions inventories, emission control strategies, and documents like policies and rules that the state can use to attain and maintain the NAAQS. And it’s not just policymakers and researchers that get a say; states are required to engage the public, through notices and public hearings, before finalizing the SIP.

Once finished, the SIPs are formally adopted by the state and submitted to the EPA for approval. Upon review, the EPA proposes to approve or disapprove all or part of each SIP. Here, the public has another opportunity to comment on the EPA’s proposed action, which the EPA factors into consideration before taking any final action on a state’s plan. If the EPA approves any part of a SIP, those control measures become enforceable in federal court—essentially giving the law “teeth.” But if a state fails to submit an approvable plan or the EPA disapproves of it entirely, it’s back to the drawing board, and the EPA is required to develop a federal implementation plan (FIP) on the state’s behalf. Usually, that’s not the best option for states, which prefer crafting strategies that take into account their own circumstances and preferences.

If this sounds like a lot of work, that’s because it is. Part of that is because thanks to sections 108 and 109 of the CAA, that work never ends. The EPA is required to continuously and periodically review their air quality standards every five years, as well as the science on which they’re based, for each criteria air pollutant and revise them as appropriate—all to keep the people and environment as healthy as possible. Taking into consideration recommendations from a group of independent scientific advisors called the Clean Air Scientific Advisory Committee (CASAC), the EPA has already revised the NAAQS for ozone three times: once in 1997, from a 1-hour standard of 120 parts per billion to an 8-hour standard of 80 parts per billion; in 2008, to 75 parts per billion; and most recently in October 2015, to 70 parts per billion. By lowering the acceptable standard, the EPA is raising the bar for air quality control and respiratory health.

The good thing is, policymakers know that regulation like this works. Air quality was a major concern leading up to the 1996 Olympics in Atlanta; event organizers wanted to see athletes choke on pressure, not on smog. Given vehicle emissions are the largest contributing factor to NOx, they went to great measures to reduce the amount of traffic downtown and encouraged people who didn’t need to be downtown to not commute or take transit at all. Epidemiological studies have shown that these efforts paid off: traffic went down by 22 percent, and with it went ozone concentrations (by 28 percent) and emergency room trips for asthma attacks (42 percent). Unfortunately, these clear conditions didn’t last; ozone shot back up in the next several years, peaking in 1999 when Atlanta suffered its worst summer on record for air pollution. Air pollution monitors showed violations for 69 out of the 150 total days of ozone season. The Sierra Club went so far as to sue the state and the EPA on behalf of Georgia’s citizens in the late 1990s as the air conditions worsened, leading to deep cuts in Atlanta’s federal highway budget.

Of course, that’s when Georgia starting getting serious about reducing its air pollution emissions, especially in the metro Atlanta area. Programs like Georgia’s Vehicle Emissions Inspection and Maintenance (I/M) Program were implemented, which ensure that vehicles on the road are periodically tested to make sure their engine pollutant emissions are in line. Lower pollution gasoline was brought to the metro area, and more than 40 counties were forced to sell this cleaner gasoline. Dozens of polluters, including Georgia Power, were hit with new rules requiring them to install emission controls for their Atlanta-area coal-fired plants. Outdoor homeowners were banned from burning their yard trimmings and land-clearing debris during ozone season. Another program mandates that any new sources of air pollution find an existing source of air pollution willing to simultaneously reduce their emissions, ensuring that atmospheric room is made for developers and ideally, the air quality won’t get worse. These local programs are enforced by a variety of supplementary federal requirements, like the current Cross-State Air Pollution Rule (CSAPR), which helps facilitate the CAA’s “good neighbor provision” requiring the EPA and states to address interstate transport of air pollution that affects downwind states’ abilities to attain and maintain NAAQS.

From the average Georgia citizen’s point of view, of course, more air pollution control programs and increasingly stringent regulation, the merrier—especially for those of us that might suffer from any preexisting respiratory conditions that ground-level ozone loves psyching out. But for the industries and fields that actively contribute to ozone pollution by emitting precursors like nitrogen oxide (NOx) and VOCs, these increasingly stringent benchmarks couldn’t be more of a hassle. Even though the general trend of Georgia’s air quality is steadily decreasing, many counties are still struggling to consistently meet the 2008 standards, with some occasionally straying back into 1997 territory in some years. In fact, Atlanta has struggled to meet federal health-based air quality standards for ground-level ozone ever since they were first established in 1991.

But federal policy is federal policy. Plus, the health problems that go hand in hand with rising ground-level ozone emissions don’t really care about the economic costs of controlling it.

Demission and Drive

For anyone that’s lived and worked in Atlanta, the answer to limiting local ground-level ozone emissions might seem blatantly clear: the city needs to provide more consistent, dependable, and robust means of public transportation. Since city officials and local policymakers also tend to be locals, this is something that they’ve been trying to work on, especially when they’re considering the influx of people the city is expected to see in the coming years. If you think rush hour traffic is bad now, imagine how much worse the roads will be when projected 2.5 million new residents move into town over the next 25 years. And according to Planning Commissioner Tim Keane at a public meeting in Buckhead last February, it’s very important that many, most, or perhaps all of those people drive a lot less than we do now, or congestion will be “unbearable.”

Rhyming aside, local air quality control officials like the sound of Keane’s statement, and the positive effects it might have on their commute and the city’s ground-level ozone levels. And even though there’s some fear that Atlanta government officials are just talking the talk, this time it looks like they’re planning to walk the walk (or maybe ride the bus) as well. Right now, the city is in the process of updating the Connect Atlanta Plan, its first comprehensive transportation plan that was adopted in 2008. A lot has changed since then, like growing by 10 percent between 2010 and 2015 alone, and topping national charts for average commute times. According to its website, Atlanta’s new and improved Transportation Plan will “provide policy and project recommendations to build a world class, sustainable transportation system that addresses congestion in our growing and evolving city” and work to “guide Atlanta’s transportation decisions to make Atlanta one of the most livable cities in the country.”

The main focus of the proposed plan so far is to reduce the reliance on cars as people’s primary form of transportation around the city. Not only are cars a much less efficient use of Atlanta’s limited space compared to public transportation or biking, but it also emits far more ozone precursors compared to ride-sharing or more environmentally friendly commute options. The priority on making buses and the Metropolitan Atlanta Rapid Transit Authority (MARTA)—the principal public transport operator in the Atlanta metropolitan area—more convenient would help keep more cars off the road and more ozone precursors out of the atmosphere. In addition, the plan will also adapt to and anticipate new ride-sharing services like Uber and Lyft (not like they could ignore the trend at this point if they tried). Of course, the strategy of improve bike paths and add needed sidewalks to encourage walking is the best option from an environmental standpoint, since people not only don’t add to ozone formation, but actually help take it out of the air for everybody else (just kidding!). Other incentive-driven options the city might be toying with include reduced prices of public transportation passes, benefits for working from home, and convenient and secure bicycle parking, in addition to discouraging people from driving through increased gas prices, decreased parking opportunities and increased rates, and reduced speeds.

The Atlanta Transportation Plan in the works wouldn’t just be wishful thinking, either—it has the financial and social power to enact real change. Last November, voters approved sales tax increases that would provide an opportunity for infrastructure improvement that could revolutionize Atlanta. Anticipating approval of the referendums, Mayor Kasim Reed said it’s the “biggest expansion of MARTA in the city’s history.” The 0.5 percent hike in the existing MARTA funding tax could raise an estimated $2.5 billion over 40 years, while a 0.4 percent increase in the five-year transportation local special option sales tax (TSPLOST) could bring in $300 million for infrastructure improvements, like streets and sidewalks. Coupled with the city’s ambitious new transportation plan, MARTA’s potential new fleet of electric buses, and the rising interest in metro Atlanta to live near public transit, there’s a good chance Atlanta’s public transportation system could get a nice makeover while also making a dent in the city’s ambient ozone levels.

While the Atlanta Transportation Plan might be a win-win for everybody in this case, generally speaking, state air quality control officials aren’t happy about the new ozone standards. But they’re more than willing to suggest where they think future ozone regulations should come from: the federal government. Last March, the Georgia Department of Natural Resources wrote a tense letter to the EPA to dispute the new 8-hour 70 parts per billion ozone level standard was being debated and ultimately passed. Keith Bentley, Chief of the Air Protection Branch at the Georgia Environmental Protection Division, wrote, “Any future reductions in measured ozone concentrations will come from federal control measures that reduce NOx emissions from on-road mobile sources, off-road mobile sources, locomotives, aircrafts, and shipping.” He continued, “There are no effective control measures left available to the state, beyond those already identified and being implemented, to reduce ozone levels in the Atlanta nonattainment area.”

It’s not just state governments that like pointing fingers when it comes to environmental regulations—it happens on an even larger scale as well. Most of this is ground-level ozone’s fault. Because it’s gaseous in nature and an outdoor air pollutant, ozone doesn’t tend to listen very well to local, state, or national boundaries. These qualities make it that much more difficult for localized regions to control and reach their environmental standards successfully, since they also have to factor in ozone that’s drifting in from the a neighboring country or state. But humans have to take some of the blame for the confusion as well. Ozone precursor emissions from international aviation and shipping are rapidly increasing; aviation emissions contribute an estimated 2 percent and international shipping an estimated 15 percent of global NOx emissions respectively, and who knows where they’ll end up. That’s why when the Royal Society, the United Kingdom’s national academy of science, discussed ground-level ozone in the 21st century, their first recommendation was to explore “options for an international mechanism to provide a globally coordinated approach to air pollution issues, and O3 specifically, should be identified and evaluated.”

Even so, people can point fingers all day, and that won’t change the air quality a bit. At a certain point, it boils down to individual decisions.

Hold Your Breath

At the end of the day, the fact that the city of Atlanta—and indeed, the world—is choosing to focus their efforts on vehicle emissions to control ground-level ozone pollution provides a natural starting point for an individual looking to do the same. The most straightforward way to help reduce air pollution on a personal level, of course, is to limit relying heavily on the driving habits that emit those pollutants in the first place. In everyday practice, this strategy might look very different depending on a person’s lifestyle and priorities. For some people, it could be combining errand-running trips to cut down on time in the car, or carpooling to work. For others, it could mean cutting out the commute entirely by exploring the option of telecommuting. As the workforce shifts, employers are increasingly exploring other flexible work options. Under the right circumstances, setting up virtual workspaces can result in a win-win situation for employer, employee, and environment. One Emory University manager said his employee was “exceptional” about working under minimal supervision.

If you still need to get around the city, another way to cut back on emissions is to explore other transportation options. Depending on where you live, mass transit might be a feasible option. In the Atlanta area, there are a variety of public transportation options that you could use. MARTA, which serves Fulton and DeKalb counties through a bus and rail system, might be the most well-known alternative to driving, but it’s not the only one. Just in the metro Atlanta area, there’s also the Atlanta Streetcar, a 2.7 mile East-West route that connects the Centennial Olympic Park area to the Martin Luther King Jr. Historic Site; the Cherokee Area Transportation System (CATS), which provides countywide transportation services for residents of Cherokee County; and Emory University’s Cliff shuttles, which provide shuttle services for students, staff, and the local community surrounding the university and the Clifton corridor, to name just a few options. There’s also resources out of state for residents in Athens, Augusta, Macon, Rome, and other neighboring counties. Consider spending your commute reading, napping, or getting some work in, while saving money on the way. A monthly MARTA Breeze Card, for instance, is only $95, compared to the approximately $335 a month that it costs to drive alone.

And while it’s easy to, try not to forget the power of your own body to get you places that you need to be. After all, more than 25 percent of all auto trips are less than a mile, which should hopefully be within your range of motion. Not only does commuting by bike or foot completely slash your own personal air pollutant emissions, it also promotes a more active lifestyle and offers significant health benefits. To get started, check out the Atlanta Bicycle Coalition, a member-based nonprofit advocate for better bicycling in Atlanta. They offer a variety of resources for those looking to incorporate biking into their transportation habits, from finding the perfect route, to financial assistance in renting or purchasing a starter bike, to offering classes about Atlanta’s new bike share program or fostering urban confidence in beginning cyclers.

There’s also other programs in the area works towards the same end. PEDS, a small advocacy group, works with transportation agencies, neighborhood organizations, and local law enforcement to bring about pedestrian-friendly policies, plans, and street designs in Georgia. The Georgia Department of Transportation (DOT) Bike and Pedestrian Program offers technical assistance, engineering, and planning guidance, public information, and educational materials and programs for cyclists and walkers. Cycle Atlanta, a smartphone app developed by Georgia Tech, uses your phone’s GPS to record your bike routes in real-time, giving transportation planners with the City of Atlanta the data they need to make Atlanta a better place to ride. This is the kind of positive feedback loop (or cycle!) sustainable city planners love. 

If you insist on continuing to use your car, however, there are still steps you can take to minimize engine emissions contributing to air pollution problems in your city. Some of the emissions, in fact, are directly under your control based on the way you drive and care for your car. Remember your first driving lessons: not only are these tips better for your safety on the road, and the safety for those around you, but they’re also valuable strategies from an ozone emissions standpoint. Small habits like limiting idling, avoiding jackrabbit starts, and driving within the speed limit are all ways you can begin to limit your ground-level ozone footprint. This mentality can also translate into routine maintenance and caring for the vehicle itself. Keep your tires properly inflated to ensure that you get the most bang for your buck (and ozone precursor emissions) out of every ounce of gasoline. And while you’re at the gas tank, stop short of topping off your gas tank, and try visiting in the evening on “Smog Alert Days” to refuel. Make sure you have your car emissions tested as required by law at a certified testing location.

Transportation, while one of the most important sectors when it comes to ozone precursor emissions, isn’t the only aspect of ground-level ozone pollution that ordinary citizens can help in. Besides your cars, keep your lawn equipment and boats periodically checked and tuned up, to make sure that emissions standards are within their limits. Try using electric or natural gas grills instead of charcoal and lighter fluid. Using environmentally-safe paints and cleaning products to cut down on VOC emissions from your home. Keep your thermostats high in the summer and low in the winter. And if you’re serious about reducing ground-level ozone pollution in your city, get involved with preexisting programs with the same vision. If you’re in Atlanta, get involved in the city’s new Transportation Plan by attending a pop-up meeting to give your two cents on the future of public transit in metro Atlanta, or take a couple minutes to fill out their publicly available survey. Check out Georgia Commute Options, a program from Georgia’s DOT that helps provide incentives and resources to help “commuters, employers and property managers take advantage of commute alternatives.” 

Even if you’re taking all these actions and going to lengths to reduce your own ozone precursor emissions, keep in mind that air pollutants aren’t exactly fair, and you and your family are still susceptible to the ground-level ozone that forms due to other’s emissions. To that end, make sure that you’re minimizing your own exposure, especially if any respiratory health condition makes you especially sensitive to the pollutant. Make it a habit to check daily Air Quality Index (AQI) forecasts for ozone. Even better, convince your organization to partner with AirNow’s Air Quality Flag Program and raise a flag corresponding to how clean or polluted the air is to help raise awareness of local air quality conditions for others. Think about spending more time indoors and choosing less strenuous outdoor activities so you don’t breathe as hard when ozone levels are high, or just planning outdoor activities at times when ozone levels are forecasted to be lower (usually in the morning and evening).

At the end of the day, we’re all in this together, because the air belongs to all of us. We’re all partly responsible for local air quality. Even if we don’t want to hold ourselves accountable, our health will.

Chapter section photos of respiratory inhaler, Earth’s atmosphere, and cyclist art used under Creative Commons licensing from the NIAID, Judy Schmidt, and Gordon Chesterman, respectively.  

Show Key Terms

Key Terms

Asthma: a common respiratory condition that causes inflammation and narrowing of the lung's airways, leading to difficulty breathing
Allergen: any substance, often a protein, that causes an allergic reaction
Asthma attack: a sudden worsening of asthma symptoms caused by the tightening of muscles around the airways (bronchospasm)
Inhaler: a portable device for administering a drug that is to be breathed in, often used for relieving asthma
Pulmonologist: a medical specialist that focuses on diseases involving the respiratory tract, from asthma to tuberculosis
Stratospheric ozone: a layer of ozone in the atmosphere that absorbs harmful solar ultraviolet (UV) radiation
Tropospheric ozone: also known as ambient or ground-level ozone; a respiratory irritant formed by air pollutants and sunlight near the Earth's surface
Nitrogen oxide (NOx): a group of gases primarily formed through fuel consumption that contributes to acid rain, tropospheric ozone, and smog
Volatile organic compounds (VOCs): carbon-containing chemicals that easily become vapors or gases and contribute to tropospheric ozone formation
Inflammation: a complex, protective biological response marked by an influx of white blood cells to localized injury; can be acute or chronic
Ozone precursor: a compound that results in the formation of ground-level ozone
Anthropogenic: originating in human activity
Isoprene: a common organic compound released by many trees in response to heat stress; the largest contributor to VOC emissions
Climate penalty: when meeting air quality standards is more difficult since climate change offsets improvements expected from emissions reductions
Criteria air pollutant: a set of air pollutants that causes health hazards

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