Air Pollution and Running: When to Ease Off the Pace

Add the day’s air to your pre-run checks, alongside the weather and the wind: a free app gives you the reading in thirty seconds and, on the worst days, shows you what to change about your run.

• The study of the six World Marathon Majors and the pollutant linked to slower times
• The European Environment Agency’s free app, available in English
• How to read the index’s six levels and the breakdown for each station
• Which pollutant to check first if you run in a city
• What to move on poor-air days, starting with the time
• A note if you have asthma

Before heading out you check the temperature, the wind, the chance of rain in the hour you care about. There’s a fourth item that deserves the same quick glance, and it’s on the same phone: the air you’ll be breathing for the whole run.

What the Study of the Six Majors Measured

On days when the air carries more nitrogen dioxide, finishing times tend to stretch, and recreational runners feel it far more than professionals. That’s what a University of Leicester study found after comparing fifteen years of results from the six World Marathon Majors, from Berlin to Tokyo, with pollution levels on race day: among amateurs, the link with nitrogen dioxide is roughly six times stronger than among elite athletes.

Take the finding for what it is. It’s an association that repeats across millions of finishes, and it makes no claim to tell you how much slower you’ll run on Tuesday morning. The other pollutant the researchers looked at, fine particulate matter, left no mark on the clock.

Nitrogen dioxide, on the other hand, comes from a clear place: traffic, which is still its main source in Europe. Think of it as the wake of a bus that has already gone by. You can’t see the bus any more and the junction is clear, but what it left behind hangs over the road and ends up in the air you breathe at the third kilometre, when your breathing has deepened and every breath draws in more of it.

That origin is exactly what makes the finding useful. You can’t change the air of an entire city, but you can decide how close you stay to its busiest roads, and at what times of day.

Reading the Air Before You Go Out

The tool already exists and it’s free: the European Air Quality Index app from the European Environment Agency, available in English and other languages for Android and iPhone. Every hour it pulls in data from thousands of monitoring stations in European cities and turns it into a level you can read at a glance.

Start by picking the right station, meaning the one closest to where you run, which isn’t always the one outside your door. If you train in a park on the other side of town, that’s where you need to look.

Then there’s the scale. The index has six levels: good, fair, moderate, poor, very poor and extremely poor. For each one, the Agency explains how to adjust. Up to moderate, anyone without breathing problems can carry on with their usual outdoor activities. From poor upwards, the advice for the general population is to consider cutting back on intense outdoor exercise, especially if you notice sore eyes, a cough or a sore throat.

The part that changes how you read it is the station breakdown. The overall level reflects the worst of the individual pollutants, up to five of them: two types of particulate matter, ozone, sulphur dioxide and nitrogen dioxide. Open the station and you see them one by one, and if you run in a city, the last one deserves your attention. Two days with the same overall level can have different causes, and when nitrogen dioxide is what’s pushing the index up, you already know where it collects: along the roads, during rush hour. That’s the reading that matters most, because it’s the only one that also tells you what to do.

The other feature worth using is the forecast. If you’ve got an interval session planned for tomorrow morning, a look the evening before is enough to decide whether to keep it or swap it for the next day’s easy run.

Seen this way, the air stops being a vague worry and becomes one more item on the list, next to the wind. It takes the same thirty seconds, and on bad days it tells you a good deal more.

The Days When It’s Worth Changing Your Run

When the level climbs and nitrogen dioxide is the main driver, you can almost always save the run by moving something, starting with the time. Go back to the bus: the wake follows the traffic, so the hours to avoid are the ones when the city is on the move by car, and the ones straight after, when the road has only just cleared. Guidance for people who exercise outdoors points the same way: away from rush hour, away from busy roads, into parks and green spaces whenever you can. Dawn, before the cars fill the avenues, has the advantage of getting there ahead of the wake.

The route matters too. A park, a riverside cycle path, a loop that stays entirely inside green space: on poor-air days, the route that keeps you away from the main through-roads is worth more than the one you know by heart, even if getting there costs you an extra ten minutes.

Then there’s how hard you push. During intense effort you take in more air, and deeper, so on those days it makes sense to save the quality session for a better day and head out for an easy run at conversational pace. It’s the same advice you’ll find in the app, applied to your week.

I’ve never seen a training block ruined by an interval session moved back two days. I have seen plenty of intervals run anyway, at the wrong hour and on the wrong road, just because they were on the plan.