How it works

Be I/O takes the fuzziness of generic guidelines and tailors them to you by making two approximations.

1. A guideline becomes a budget

The World Health Organization’s 2021 guidelines suggest a daily average of less than 15 µg/m³ of PM2.5. PM2.5 is particulate matter smaller than 2.5 microns – the stuff that does the most damage.

This guidance is epidemiological, and is great for broad, generalized, and simple guidance. But it isn’t very useful if you know the air isn’t great but you only want to spend an hour in it, and will be inside the rest of the day.

Be I/O takes this guidance, and reverse engineers it.

This guidance is for the average person, and the average person breathes 15m³ of air per day. So we can approximate that the average person has a daily budget of *225µg of PM2.5.

2. A heart rate becomes a volume of air

How much you take in is how much air you moved times what was in it. The first half comes from your heart.

Be I/O uses a model called D1 to estimate the volume of air you breathe at a given heart rate. The more details you provide – age, weight, height, min/max heart rate – the better the ventilation estimate.

For nerd athletes who know their ventilation rates from a recent metabolic test, you can skip the estimates and enter the metabolic readings directly.

None of this leaves your phone. See Privacy.

3. The two become a verdict

When you’re planning your day, select the activities you’d like to do outside, and Be I/O will calculate your PM2.5 intake based on the air quality near you, your predicted heart rate and duration of each activity, and the remainder of the day inside.

If you push it past the limit, you can either take the advice and stay inside, or plan lighter or shorter activities.

It’s a model, and it’s wrong in the way all models are. But at least it’s not arbitrary.