Based on 2019 data I analyzed the concentration of Nitrogen Dioxide (NO2) and Particulate Matter (PM2.5), when available, as they are two of the most common pollutants in urban environments due to vehicle traffic and household heating.
In a recent study, scientists selected 140,072 adults and after following them for an average of 2 years, they found that physical activity, even in high PM2.5 levels, is an important high blood pressure (hypertension) prevention strategy as the markers remained stable.
This is a great piece of news. However, I prefer to avoid pollution in the first place and not playing the constant game of good and bad. In our lives, many other factors contribute to health issues, and by eliminating air pollution you make sure that the eternal battle of survivor leans towards your favor.
Let’s take some random locations from across England and see which day and time of the week is the best to exercise outdoors. All data are from the official monitoring network (AURN).
London
I randomly chose to analyze data from the London Marylebone Road (MY1), which is an urban traffic station.
Based on the NO2 data, from Tuesday to Friday I don’t recommend anyone to run near that area as the highest concentrations are registered those days especially between 07:00 to 21:00 throughout the year. Remember the annual safe mean according to WHO is set to 40 μg/m3. Weekends and late nights between 00:00 to 06:00 in the morning seem to be adequate to exercise as traffic seems to calm down a lot. January, February, March, and June are the worst months too.
Based on the particulate matter data with an aerodynamic diameter smaller than 2.5 microns (PM2.5) and according to WHO, which has set a safe annual mean to 10 μg/m3, athletes shouldn’t exercise at all, with the worst months January, February, March, April, and May. The PM2.5 pollution is a byproduct of a combination of the traffic but also the household heating systems (biomass, oil, wood, etc).
York
Once more, I randomly chose a site in York, more specifically the York Heworth Green (YK13), which is a road station. Unfortunately, this station has only a NO2 monitor and no PM2.5.
From the NO2 data, we can see that in comparison to London’s MY1 station, the air quality is much better with lower concentrations throughout the year. Weekends and late nights are the best moments to exercise, midday looks fine too. The best months for outdoor activities according to the NO2 data are during summer, July, and August. Keep in mind, sunlight radiation can turn NO2 gas into ground-level ozone (O3), but the station doesn’t measure O3.
Sheffield
I will admit that I chose Sheffield because I know some people there and I wanted to learn when is the best time for them to do activities outdoors. The air quality station is in Sheffield Barnsley Road (SHBR), and it is an urban traffic station.
Once more, we can see that weekends are the best time of the week to do activities as people don’t commute to work. August by far the best month of the year too. I did a bit further analysis of the data for Sheffield, and I combined some surface meteorological data (wind speed and wind direction) to figure out the origin of the pollutants. During winter, the wind speeds are higher than in summer, and the high concentrations of NO2 come from the west.
Household heating contributes a lot of PM2.5 pollution in the area during the winter months. People in Sheffield could have breathed a lot fewer particles if they had invested in zero-emission heating solutions. During summer, the pollutant is almost gone because wood burners are not active. A wood stove emits more harmful air particulates (PM2.5 & PM10) than a diesel truck. Midday seems to be the best time to work out if you want to avoid breathing fine particles that can reach your lungs, heart and even your brain.
Conclusion
Although in a recent study researchers believe that urban exercise counteracts a dangerous effect of air pollution, I would suggest avoiding exercising in busy roads and choosing a green park for your workouts. Air pollution is sneaky.
Would you like to read a similar analysis for your location in the future, then leave a comment below.
See The Air 
Very interesting article, Sotirios. Thanks. I wish we could do these analyses for other cities and locations as well.
Please correct me if I am wrong, because these data corroborate even further a serious question I have about Athens, Greece. I see that in the UK people are so much worried about air pollution even when the levels are just a bit higher than the safe level. This is good of course. The government issues alerts, people and communities do worry and look for solutions, and programs are in place in order to reduce air pollution. Just look at what the major of London has managed to do in only a few years.
Here in Athens, no one says anything even though the air quality is so much worse than in the UK. The government does not raise alerts, people don’t complain, the major doesn’t even think about planning a cleanup of the city air, no one makes a sound. Breathing polluted air is just the norm over here. Why bother.
PM2,5 is very rarely below the safety level in Athens even in summer, and most of the time it is above 20μg/m3. In winter it goes over to 100-150 for so many nights and cold days because of wood stoves and fireplaces. I am not making this up, my PurpleAir sensor on my terrace tells me this. And the other Purple Air and iQAir sensors around the city tell this. Forget about the outdated official government’s sensors, because those only give data for PM10, not PM2,5.
I really wonder how PM2,5 can be so low in Sheffield in winter, with wood stoves warming up homes. From an athenian point of view, people of Sheffield are very lucky to breathe much less polluted air than us. And it is not only Sheffield. I see this in many other cities around the world. The air is simply better than in Athens and other cities of Greece, even if so people and groups over there complain about too many wood stoves in their neighbourhoods. They should come to Greece to see what it really means to be chocking in smoke all winter.
So my question is: please do your statistics about Athens too, let us know what the air is really like compared to other major cities because to my knowledge no one has done so yet and we really need clear data in order to press the local authorities and government to finally start doing something. Especially now that we are told that we need to aerate our homes and buildings to keep the COVID at bay. How can we open the windows when there is so much toxic air outside???? We are told that there are so much carcinogenic chemicals in wood smoke, so how can we keep that outside of schools, offices and homes that must keep their windows open? And isn’t air pollution making the effects of COVID on our organism worse? So what to do?
And, to keep to the subject of this post about exercising outdoors, when would be the best time for Athenians to do jogging? I am afraid that in winter there would be hardly any such time.
Thanks again for all your work!
Andrea
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Thank you Andrea for your message.
Send me your purple air data and I will try to find the official data for Athens, hopefully they are in the European Network, it will be nice to compare them with your data too.
People in the UK use high efficiency certified wood burning appliances which are more efficient than common fireplaces. Both produce PM2.5 & PM10 but common fireplaces are the worst.
I was there last Christmas and the air was unbreathable and they knew it but they didn’t care as long as their houses don’t smell. 🙄
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Thanks so much Sotirios for offering your help! I will send you the data in a private email.
If you were here at Xmas, then you know what I am talking about! That has to eventually stop, even though it will surely take much longer to reach that goal than in the UK… But I am part of a group of citizens that started the discussion about air quality here in Athens, and we are planning to begin collaborating with schools in order to educate people about the issue. Hopefully this will help to get result sooner than hoped…
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