When companies adopt eco-friendly practices, the air-quality outcomes can vary dramatically. Many organizations are taking steps to shrink their carbon footprint, whether by sourcing electricity from renewables or by cutting air travel. Each action reduces greenhouse gases, but which delivers bigger benefits for society?
To begin addressing this, MIT researchers found that even when both activities cut the same amount of carbon dioxide, their effects on air quality can differ substantially. Using a comprehensive modeling framework and data from three organizations, they quantified how each action impacts air quality, and they found that aviation tends to inflict about three times as much damage to air quality as equivalent electricity purchases.
Exposure to major pollutants like ground-level ozone and fine particulate matter can drive cardiovascular and respiratory illnesses and even shorten lifespans.
Air-quality effects also vary widely by location. The study shows that decarbonization actions influence pollution on different scales. For organizations in the northeastern United States, energy-use changes tend to affect the local region, while the air-travel footprint is felt globally because most emissions occur at higher altitudes and are carried by winds across continents.
The researchers aim to help organizations prioritize climate actions for the strongest near-term health benefits. Noelle Selin of MIT notes that pursuing net-zero emissions can have very different implications for air quality and health, depending on how reductions are structured. The study’s coauthors include MIT researchers Yuang (Albert) Chen, Florian Allroggen, and Evan Gibney, along with Sebastian D. Eastham of Imperial College London and William Clark of Harvard University, and the work appeared in Environmental Research Letters.
A challenge to quantify
Climate studies often emphasize the air-quality advantages of regional or national policies because those effects are easier to model at scale. In contrast, corporate or institutional efforts to go green are harder to gauge since they operate within larger societal systems and interact with broader policy landscapes.
To tackle this complexity, the team drew on data from two universities and a company in the Boston area. They asked whether actions that remove the same amount of CO2 would yield the same air-quality benefits, and the answer was: not at all. CO2’s impact is global, but air-quality effects hinge on local pollutants, which makes location crucial.
Burning fossil fuels releases nitrogen oxides and sulfur dioxide alongside CO2. These co-pollutants react in the atmosphere to form fine particles and ground-level ozone—the main components of smog. Different fuels emit varying levels of these co-pollutants, and local weather, existing emissions, and population patterns shape how smog develops and whom it affects. As Selin explains, you can’t assume equal near-term sustainability benefits from all CO2-reduction strategies without accounting for these other emissions.
The study used an integrated, systems-level approach that linked energy use and flight data to a network of models. This setup incorporated power-plant emissions data, established links between air quality and mortality, and aviation emissions tied to specific routes, feeding into an atmospheric chemistry transport model to estimate both air-quality and climate effects.
The scope of this system posed numerous challenges, and the team conducted multiple sensitivity analyses to ensure the pipeline functioned correctly, as Chen notes.
Measuring air-quality impacts
To compare climate and air-quality effects on a common footing, the researchers monetized the impacts. Drawing on prior literature, a carbon-dioxide–related climate damage figure is about $170 per ton (in 2015 dollars). Applying the same framework to air quality, they found that electricity-driven decarbonization carries about $88 per ton in additional air-quality damages per CO2 ton, while aviation carries about $265 per ton. This underscores that the location and manner of emissions dramatically shape air-quality costs.
A striking finding was the far-reaching reach of aviation emissions. Aviation not only imposes greater harm but also distributes its impacts globally, affecting people far from the emission source. High-altitude releases and international winds spread pollutants widely, with nations like India and China experiencing outsized effects because of higher baseline ground-level pollution that worsens smog formation.
The team also dug into shorter flights. They found that regional, short-haul trips tend to impact local air quality more than longer domestic flights, suggesting that prioritizing reductions in short hops could yield tangible neighborhood benefits, according to Selin.
Even within electricity purchases, location matters. A university’s emissions might occur over a densely populated region, while the corporation’s emissions fall over a sparser area, leading to different estimated health outcomes. In one example, the university’s emissions were linked to 16 percent more premature deaths than the corporation’s, despite identical climate impacts.
The takeaway is clear: achieving net-zero while advancing overall sustainability depends heavily on which CO2 sources are eliminated first, and where they are eliminated. As Chen puts it, the order of reductions matters a great deal for near-term health and air quality.
Looking ahead, the researchers plan to quantify air-quality and climate effects for train travel to evaluate whether replacing short-haul flights with rail could offer additional benefits. They also want to explore the air-quality implications of other energy sources in the United States, such as data centers.
Funding for this work came from Biogen, the Italian Ministry for Environment, and the MIT Center for Sustainability Science and Strategy.
