Air pollution doesn’t stop at borders. A wildfire burning in Canada can send smoke curling across the Atlantic, producing great sunsets in London. Storms born in the Sahara Desert can drift across the Atlantic Ocean and become hurricanes that eventually crash into the U.S. Gulf Coast. Local pollution events have global consequences, often in ways that are invisible to the naked eye but deeply felt in our lungs, ecosystems, and economies.
Few people understand this better than Dr. Jim McQuaid, an atmospheric scientist at the University of Leeds. For more than 25 years, his work has ranged from measuring dust storms over the Sahara to studying smoke from Indonesian peatland fires, from ice-nucleating particles in clouds to community air monitoring in West Yorkshire. His career illustrates a central truth: the atmosphere is one of the world’s great connectors, tying together distant places and people through chemistry, physics, and weather.
In this piece, I draw on Jim’s perspective to explore what atmospheric science teaches us about the hidden pathways of pollution, why they matter for climate, health, and justice, and how science and technology can help us make them visible.
From Chemistry to the Sky: The Science of the Atmosphere
Jim didn’t start as a climate scientist. His foundation was actually in chemistry, but it was this that pointed him upward, to the atmosphere. He describes the air around us as a kind of giant cauldron: chemists add the ingredients, physicists turn up the heat, and meteorologists stir the pot. The result is a constantly shifting mixture of gases, particles, and reactions that shapes the air we breathe.
This interdisciplinary view is crucial. You can’t understand pollution without chemistry. You can’t understand its transport without physics. And you can’t predict its impacts without meteorology and data science. The atmosphere is a system of systems, and science has to cross boundaries in the same way pollutants do.
Measuring and Modeling: Two Sides of the Same Coin
How do we study something as vast and dynamic as the atmosphere? Jim explains that there are two main approaches: measuring and modeling.
On the ground and in the sky, instruments measure what’s happening in real time. Jim has flown on research aircraft over Brazil and across Saharan dust plumes, gathering samples and tracking particle chemistry. At the same time, in labs and universities, scientists analyze those samples with tools like Python, R, and mass spectrometry, piecing together the chemical jigsaw puzzle, a puzzle with many pieces, as he often tells people.
Then there are models, massive computer simulations run on supercomputers, where the atmosphere is represented by physics and chemistry equations. These models don’t just predict tomorrow’s weather. They are also used to estimate how changes in climate will ripple through agriculture, health, and economies. Some of the biggest supercomputers on the planet are tasked with providing us with the highly detailed weather forecasts that we all rely on. They allow scientists to add more and more complexity to their climate simulations as well. Essentially, the more information, data, and equations we can incorporate into these models, the better the output. The new supercomputer, which the UK Met Office has just started using, costs over one billion pounds; it is generally expected to pay for itself within a couple of years as it allows the country and industry to prepare for storms, which can be hugely costly to the economy.
As Jim puts it, every forecast has a financial weight attached to it, from wheat prices after a hailstorm to the insurance costs of hurricane seasons.
Observations anchor reality. Models project possibility. Both are essential.
Pollution’s Global Ripples
The atmosphere linked local events to global consequences in ways that often surprise us.
- A hailstorm in the U.S. Midwest doesn’t just damage crops; it shifts global wheat prices
- Storms born in Sub-Saharan Africa can drift across the Atlantic, transforming into hurricanes that fuel devastation thousands of miles away. Research has shown links between these, known as Eastern African Waves, and storms like Hurricane Katrina. Surprisingly, the Sahara can also reduce the strength of hurricanes, as mineral dust blown across the Atlantic can act as a sunshade, shielding the Gulf Coast and Caribbean from the sun, which in turn cools the sea surface. Ultimately, the warmer the ocean, the more energy it has to drive the ferocious winds that become hurricanes.
- Wildfire smoke from North America can travel across oceans and haze the skies over the UK.
Part of this comes down to the lifetime of pollutants. Some, like nitrogen dioxide (NO2), only survive a few days in the atmosphere before breaking down. Others, such as fine particulate matter (PM2.5), can remain suspended for weeks, long enough to cross entire continents.
This is why meteorology and chemistry must be studied together. Without chemistry, you don’t know what the particles are doing. Without meteorology, you don’t know where they’re going. This means that it takes a real teamwork approach to understanding the atmospheric processes above our heads.
Shifting Scales: From Global Dust to Local Streets
After years of studying global atmospheric patterns, Jim increasingly turned his attention to the local scale: streets, schools, and homes.
The rise of electric vehicles, for example, reduces nitrogen dioxide from traffic but changes the mix of pollutants in urban air. Fireworks, though fleeting, are among the most predictable pollution events of the year, creating sudden spikes of particulate matter. Indoors, candles, cooking, and restaurant stoves release particles that often rival outdoor sources but receive far less public attention.
From Sahara dust to kitchen smoke, Jim emphasizes, the scales may differ, but the principle is the same: what we breathe is shaped by invisible chemistry and movement.
Visualizing Pollution: Air Quality Stripes
Science can measure and model the atmosphere with incredible precision, but how do you share that story with the public?
Inspired by Ed Hawkins’ iconic “climate stripes,” Jim and colleague Dr. Kirsty Pringle created Air Quality Stripes. Instead of numbers or charts, the stripes use simple bands of color to illustrate changes in PM2.5 levels from the Industrial Revolution to the present day.
The power lies in the simplicity. You don’t need a PhD to see the trend. The visualization invites questions: Why do the stripes get darker? What changed in the 20th century? What does it mean for me?
It’s science as a conversation starter, designed for everyone, not just researchers. “We wanted people to talk about air pollution in the same way they talk about the weather, we didn’t want someone to need to have university-level science to understand it”, explains Jim, “if people talk about it on the bus, then I would feel we have scored a goal!”
Air Quality Stories: Making it Personal
For Jim, data only comes alive when it’s tied to human stories.
He recalls stories of the London smogs of the 1950s, where drivers navigated by following the painted lines on roads because visibility dropped to zero. More recently, he points to July 4th fireworks in the U.S., which create measurable waves of PM2.5 that ripple westward across four time zones in a single night.
Even everyday choices matter. Do you walk along a busy road or take a side street? Do you cycle instead of driving? Do you burn candles indoors? Each decision creates an exposure story, whether we’re aware of it or not.
Technology and the Democratization of Air Science
The past decade has seen a revolution in low-cost sensors, making air pollution visible in ways once limited to labs and satellites.
Working with colleagues, Jim built a network of more than 60 sensors across Leeds—the largest in the UK outside of London. These sensors provide hyperlocal, real-time data, showing how pollution spikes at school drop-off times or how air quality varies block by block. The government network provides data every hour, whereas Jim’s network does this every 2 minutes, fast enough to detect pulses of pollution as traffic signals change in the city center.
This democratization of air science has ripple effects. In Colorado, for example, athletes check local smoke levels before deciding whether to train outdoors. Parents and communities use the data to advocate for safer environments.
Yet the global picture remains uneven. The Global South, where pollution burdens are highest, often lacks the monitoring infrastructure to measure what’s happening in the air. Filling those gaps is one of the great challenges ahead.
Why It Matters: Air Pollution, Equity, and Global Health
Air pollution is not distributed equally. In many Western countries, regulations have led to cleaner air over the past decades. But in places like India and Pakistan, air pollution levels remain among the highest in the world. Children growing up in these regions face lifelong health impacts, from reduced lung capacity to increased mortality. Jim points to a project that calculates the Air Quality Life Index (AQLI) every year for all countries, https://aqli.epic.uchicago.edu/. The most recent data shows that, in 2023, the average person in the world would have gained nearly 2 years of life expectancy if the fine particle pollution was reduced to the WHO guideline level, which equates to over 15 Billion “life-years” gained. “The AQLI is a genius concept, super easy and yet illustrates the huge global impact of air pollution,” says Jim.
Pollution is also an issue of justice. In wealthy nations, crop loss from ozone pollution may mean financial hardship. In poorer nations, it can mean hunger and starvation. The same particles that cool a local neighborhood may darken the Greenland ice sheet, accelerating global warming.
And while regulatory agencies set “safe limits,” Jim stresses that no level of pollution is truly safe. Every reduction counts.
Conclusion: Pollution Without Borders
What Jim’s work ultimately shows is that air pollution isn’t just a story of chemistry and physics—it’s a story of people. Behind every dataset are families deciding whether it’s safe to walk to school, farmers whose crops depend on clean air and stable weather, and communities whose health is shaped by forces they can’t always see.
Tools like Air Quality Stripes, community sensor networks, and public storytelling make those invisible forces visible. They give us the power to notice, to question, and to demand change.
Cleaner air is not simply a scientific challenge—it’s a matter of equity, of justice, and of human rights. The borders on our maps may divide nations, but in the air above us, everything is connected. And that means the responsibility for action is shared.