We obsess over pace, weekly mileage and shoes, but almost never over the air we breathe while we run. In 2025, with more and more low-emission zones and pollution alerts in major cities, ignoring air quality is no longer an option for runners, especially if most of your training happens in urban environments.
The good news is simple: running is still one of the best “medicines” we have. But recent science is showing that when air pollution levels are high, the impact on your heart, lungs and performance can be significant, and in extreme situations it can partly offset the benefits of exercise. The goal is not to stop running, but to plan better when, where and how hard you train.
Why air pollution matters so much for runners
When you run, your ventilation can increase by a factor of 10 to 20 compared to rest. That means if the air is polluted, you’ll inhale many more particles per minute, and they will reach deeper into your lungs because you breathe mainly through your mouth and with greater force.
The pollutants that matter most for runners are:
- PM2.5 and PM10: tiny particles that can reach the deepest parts of the lungs and even enter the bloodstream.
- NO2 (nitrogen dioxide): strongly linked to road traffic, especially diesel engines.
- O3 (ground-level ozone): increases with heat and sunlight, common in many summer pollution episodes.
The latest World Health Organization (WHO) air-quality guidelines recommend keeping annual average PM2.5 below 5 μg/m3, and 24-hour exposures under 15 μg/m3 more than just a few days per year. Many European and global cities still exceed those thresholds regularly, particularly during heavy traffic, thermal inversions or sand-dust intrusions.
Recent studies focusing on endurance runners point in the same direction:
- Research on marathoners and long-distance runners has shown that on days with higher PM2.5, average marathon finish times tend to be slower and perceived exertion higher, even with similar training status.
- Analyses of multi-year marathon results found a clear relationship between poorer air quality and slower average performances, especially in long-distance road races.
- New work on exercise and pollution suggests that while the negative effects of dirty air are real, the benefits of regular physical activity still outweigh the risks in most situations. In practice, the smart move is to adjust your training to the air quality you’re facing on each day, not to give up running.
As a runner, you can’t control city traffic, but you can decide which days you run outside, at what time, where and at what intensity. That’s where air quality becomes just another training variable you should know how to use.
How to read air quality indexes as a runner
Most countries publish their own national air quality index, and in Europe the European Environment Agency maintains the European Air Quality Index, a map that shows color-coded air quality levels for every city and monitoring station.
Although names and thresholds vary by region, most systems use similar categories:
- Good: air is suitable for outdoor exercise for the general population.
- Moderate (or “fair”): training is fine for most people; sensitive individuals may want to avoid very long or maximal efforts.
- Poor: it’s wiser to shorten your outdoor workout, reduce intensity and stay away from heavy traffic corridors.
- Very poor / extremely poor: intense outdoor exercise is discouraged, especially for anyone with asthma, heart or respiratory conditions.
Practical thresholds to guide your training decisions
Without going too deep into national legal limits, you can translate air quality into training choices with a simple rule of thumb:
- “Good” index / PM2.5 below ~10–15 μg/m3: it’s safe to do any type of session outdoors (intervals, tempo runs, long runs).
- “Moderate” index / PM2.5 between ~15 and 25 μg/m3: still acceptable for most people, but if you’re very sensitive, favor easy and steady runs in parks or green areas.
- “Poor” index / PM2.5 between ~25 and 35 μg/m3: skip high-intensity workouts. Opt for easy runs, drills and strength work, and stay away from major roads.
- “Very poor” index / PM2.5 above ~35 μg/m3: this is when a treadmill or indoor cross training makes much more sense. If you still choose to run outside, keep the effort very easy and the duration short.
These ranges are indicative and don’t replace medical advice, but they give you a very practical framework: the worse the air, the easier and shorter your outdoor session should be – or the more you should consider moving it indoors.
Strategies to reduce your exposure when you run in the city
Air pollution is not an on/off switch. Levels change by neighborhood, time of day and weather. The upside is that a few small choices can dramatically cut down your exposure without sacrificing your weekly mileage.
1. Pick the right time: avoid rush hours
Whenever possible, try to run:
- Early in the morning, before the main commute starts.
- Later in the evening, once traffic and congestion have eased.
- On hot, sunny days, be wary of afternoon ozone peaks; in those cases, mornings are often the safer window for workouts.
2. Redesign your routes: fewer cars, more green
Not all kilometers are equal from an air-quality standpoint. A loop next to a ring road is very different from one through a park or along a river, even within the same city.
- Prioritize parks, riverside paths and low-traffic streets over multi-lane avenues.
- Avoid tunnels, major intersections and large roundabouts, which tend to be NO2 hotspots.
- If you use route apps like SnapRace, save “green” versions of your usual loops so you always have a lower-traffic alternative ready.
Sometimes shifting your route just one or two blocks away from a main road and into residential streets is enough to significantly reduce your exposure to exhaust fumes.
3. Match the workout type to the air quality
There’s little point in scheduling your hardest interval session on the exact day the index goes “very poor”. A simple pattern you can follow:
- Green days (good air): perfect for intervals, tempo runs and demanding long runs.
- Yellow days (moderate): stick to the plan but try to do quality work in green areas and shorten the hard segments if you feel unusually taxed.
- Orange days (poor): swap high-intensity workouts for easy runs or indoor strength training.
- Red days (very poor): your best options are the treadmill, indoor cross training or a rest day. Your lungs will thank you later.
4. Face masks: when they help and when they don’t
Filtering masks (such as FFP2 respirators) can reduce the amount of fine particles you inhale, but they also increase breathing resistance and are rarely comfortable at high intensities. As a rough guide:
- For easy runs on mildly polluted days, a mask may be an option for very sensitive or medically advised runners.
- For intervals, hill repeats or races, masks are usually a poor choice: they make it harder to breathe and to listen to your body’s signals.
- If air quality is so bad that you feel you “need” a mask to run, it’s probably smarter to move the session indoors that day.
5. Warning signs during your run
Even if you’re healthy, it’s worth paying extra attention to how you feel when running in polluted conditions:
- Persistent coughing or burning in your throat or chest.
- Wheezing or unusual shortness of breath at paces that normally feel easy.
- Dizziness, chest tightness or a sense that “something is off” that doesn’t match the effort.
If you notice any of these, slow down immediately, switch to walking and, if symptoms don’t improve within a few minutes, call it a day and get to a cleaner environment. If symptoms are intense or persist afterwards, contact a healthcare professional.
Apps and tools to check air quality before you head out
One of the perks of running in 2025 is that you don’t have to guess how the air is: you can check it in seconds on your phone. Some particularly useful tools for runners include:
- National air quality apps and websites: many countries now offer official apps that pull real-time data from monitoring stations and color-code the air quality index so anyone can understand it at a glance.
- European Air Quality Index: the European Environment Agency’s interactive map, ideal if you travel around Europe for races or work.
- IQAir AirVisual: a global app combining official data and validated sensors, with real-time maps, 48-hour forecasts and specific guidance for athletes and outdoor activities.
- Plume Labs: Air Quality: provides street-by-street maps in many big cities, 72-hour pollution forecasts and smart notifications about the best moments of the day to exercise outside.
Think of these tools as the weather forecast for your lungs. The same way you check for rain or wind to choose shoes and layers, you can check the air quality to decide what kind of session makes the most sense today.
Make air quality part of your season planning
If you live and train in a city, air quality isn’t a random detail – it’s a background variable in your whole season. Here are a few ways to include it without overcomplicating your life:
- Design three core routes in your favorite app (for example, SnapRace): one urban and fast, one green with lower traffic, and one close to a gym or treadmill option.
- Assign each workout type to an air quality range: green days for speed and tempo, moderate days for steady runs, poor days for strength or indoor sessions.
- When training for a key race (half marathon, marathon), try to schedule your long runs on weekends with reasonably good air: you can shift them by a day or two if the forecast shows a strong pollution episode.
- Review air quality the same way you review your heart rate: don’t obsess over it, but treat it as another useful signal. If the index is poor and you already feel tired, that’s a strong hint to go easier.
Running in the city in 2025 means coexisting with air pollution – but not surrendering to it. With a bit of planning, the right tech tools and some flexibility in your schedule, you can keep chasing big goals without ignoring the air that fuels every stride.
Your heart and lungs don’t just need smart training; they also need an environment that lets them perform and recover. From now on, every time you lace up and check the weather, add a new habit: check the air quality and adjust your plan. It’s a small step that, repeated week after week, will make you a fitter, smarter and, above all, healthier runner.