Greenhouse gas emissions are often considered to be interchangeable with all air pollutants. Criteria pollutants and greenhouse gases are both major contributors to harmful emissions, but they do so in distinctly different ways.
When we talk about global warming and pollution, most people are familiar with the term “greenhouse gases” however, they may not be as familiar with the term “criteria pollutants.” Both are emissions that interact in the air, contributing to the global climate crisis with detrimental effects on both human health and the environment. But there is a distinct difference between emissions that cause global warming versus those that cause air pollution, and they are treated and regulated differently.
Criteria pollutants and greenhouse gases are both major contributors to harmful emissions, but there is a distinct difference between emissions that cause global warming versus those that cause air pollution.
Greenhouse Gas Emissions Cause Global Warming
Greenhouse gases (GHG) reside in the earth’s atmosphere trapping heat and warming the planet. These gases include carbon dioxide, methane, nitrous oxide, and fluorinated gases. Much like the glass of a greenhouse, from which they get their name, GHGs let sunlight through the atmosphere but prevent the heat that they generate from escaping back into space. We need these naturally occurring gases to sustain life on Earth and help regulate global temperatures—without them the planet would be too cold, and our oceans would freeze.
Before the industrial revolution, the global GHG balance remained essentially stable as natural processes removed as much GHG emissions as they released. However, modern human activity has significantly increased the level of GHGs emitted into the atmosphere, which subsequently increases the warmth of the planet beyond sustainable levels.
Carbon Dioxide (CO2) is the primary GHG emitted through human activities, accounting for about 82% of all GHG emissions in the US, and 65% globally, according to the Environmental Protection Agency (EPA). Today’s atmosphere contains 42% more carbon dioxide than it did at the start of the industrial era.
Methane accounts for about 16% of the planet’s GHG emissions. Human activities are the major driver of methane emissions including the production and use of gas and petroleum, agriculture, waste from landfills, and treatment of wastewater. Methane is a short-lived climate pollutant (SLCP) that is 25 times more powerful than CO2 in trapping heat in the atmosphere over a 100-year period.
Greenhouse gases (GHG) reside in the earth’s atmosphere trapping heat and warming the planet. These gases include carbon dioxide, methane, nitrous oxide, and fluorinated gases.
While nitrous oxide (N2O) and fluorinated gases account for less than 10% of GHG in the atmosphere, they are also the longest lasting of the GHGs. Human activity accounts for 40% of all N2O emission, mainly coming from agriculture, transportation, industrial processes, and treatment of wastewater. It typically lasts about 115 years in the atmosphere and is 300 times more potent than CO2—meaning that the impact of one pound of N2O on warming the atmosphere is almost 300 times that of one pound of CO2.
Unlike the other GHGs, fluorinated gases have no natural emissions and are created by human activity, mainly from refrigerants, as a byproduct of aluminum production, and electricity transmission. They can last thousands of years in the atmosphere.
Because GHGs remain in the atmosphere long enough to mix, the amount of each gas is distributed equally across the globe, regardless of the source of the original emission. Burning fossil fuels for electricity, heat, and transportation remains the largest contributor of GHG emissions.
Criteria Pollutants are Responsible for Unhealthy Air Quality
Criteria pollutants are those that create poor air quality, which can damage human health as well as the environment. These include carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide. Breathing in these pollutants has been linked to a significant increase in lung and respiratory issues, heart disease, childhood development issues, cognitive impairment, and premature death. Impacts on the environment from criteria pollutants include dangerous levels of smog, acid rain, and water pollution.
Criteria pollutants are those that create poor air quality, which can damage human health as well as the environment. These include carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide.
Photochemical smog—perhaps the most commonly known and most visible form of air pollution – forms when sunlight reacts with nitrogen oxides (commonly referred to as “NOx”) and at least one volatile organic compound (VOC) in the atmosphere. When these chemicals react with sunlight, they form airborne particles and ground-level ozone, otherwise known as smog.
Air pollution was responsible for an estimated 4.2 million deaths worldwide in 2015, and millions more fell ill from breathing dirty air, according to the Global Bureau of Diseases Study. In the same year in the US, air pollution caused more premature deaths than diabetes and the flu.
Much like GHGs, industrial activity, transportation, and agriculture are the greatest contributors of criteria pollutants. Unlike GHGs, however, criteria pollutants typically remain in their geographical region. Any region can experience poor air quality, but major cities experience significantly higher levels of pollution due to increased road traffic. A region or city’s geography— mountains, air pressure systems, lack of air flow—can also contribute to how pollution is concentrated, making some areas, for instance, Los Angeles, especially prone to pollution.
Under the Clean Air Act, the EPA regulates levels of these substances based on the severity of their effects on human health and the environment, setting standards for each region. Overall, air quality has improved significantly nationwide since the implementation of the Clean Air Act in 1963, reaching their lowest levels in 2016.
However, a recent study by Carnegie Mellon shows that air pollution in the US has actually worsened since 2017, due to more transportation, an increase in the number and severity of wildfires, and recent rollbacks of EPA regulations. The study estimates that in 2018, nearly 10,000 lives would have been saved had pollution levels remained at their 2016 levels.
The transportation sector—the movement of people and goods by cars, trucks, trains, ships, airplanes, and other vehicles— is the biggest contributor to both GHG emissions and criteria pollutants.
Transportation is a Major Contributor to Both Emissions
The transportation sector—the movement of people and goods by cars, trucks, trains, ships, airplanes, and other vehicles— is the biggest contributor to both GHG emissions and criteria pollutants. In 2017, the transportation industry accounted for about 30% of total US GHG emissions, over 55% of nitrous oxide emissions, and nearly 75% of carbon monoxide emissions, according to the EPA.
Passenger cars and light-duty trucks are responsible for over half of the emissions from the transportation sector, while the remainder of emissions come from other modes of transportation, including freight movement and commercial transportation.
Emissions from this sector have continued to rise over the last three decades as population growth, urban sprawl, and increased e-commerce have spurred demand for the transport of people and goods. This trend is not expected to slow down anytime soon. Today, about 50% of the world’s population lives in urbans areas, and that is projected to increase to 60% by 2030, according to a McKinsey report. Following that growth, today’s 1.2 billion cars on the road are expected to double in the same time period, while the International Transport Forum predicts freight movement to triple by 2050.
Advancements in transportation are necessary
So, the question remains, how do we reduce emissions, improve air quality, and ensure economic growth in the face of a growing population and mobility expansion? Solving the world’s mobility challenge requires bold, coordinated efforts by both the public and private sectors, focusing efforts on improving both fuel and vehicle technology, freight and travel efficiency, and public transit systems that can remove vehicles from the road altogether.
Solving the world’s mobility challenge requires focusing efforts on improving both fuel and vehicle technology, freight and travel efficiency, and public transit systems that can remove vehicles from the road altogether.
We’ve made great strides in the last few decades as today’s vehicles are far from the polluters of years past and many US cities are experiencing greatly improved air quality from past decades. Electric and hydrogen vehicles produce no tailpipe emissions, while others such as hybrid electric, natural gas and propane vehicles emit significantly fewer pollutants than conventional petroleum-powered vehicles. It is important to remember that emissions created during the fuel production process—not just tailpipe emissions—must also be taken into account and present an opportunity for further improvements.
States, nations, and the global community are setting aggressive zero-emission goals to guide businesses and the public to transition to cleaner, more fuel-efficient transportation. Moving forward, vehicle manufacturers’ advancements in implementing cleaner fuels and technology options will get us even closer to significant emission reductions. Leadership and ambitious commitments to sustainable manufacturing, supply chains, and transportation will also be essential in reducing emissions at scale.
