Few people stop to think about it, but outdoor activities are a major influence on indoor air quality. Outdoor emissions are a significant contributing factor to the quality and breathability of air inside the buildings where we all live, work, and spend most of our time each day. According to the EPA, the average American spends roughly 90% of their time indoors.

While most everyone is aware that outdoor air pollution can impact their health, few realize that indoor air pollutants are of equal — if not greater — importance. In fact, studies have shown that indoor carbon dioxide concentrations are often 2–5 times higher than outdoors. Indoor air quality has been listed amongst one of the top five environmental risks to public health.

In the early days of Aclima, we spent a lot of time experimenting with potential applications for the data generated by our indoor sensor networks. Looking through a year of environmental data, we discovered two examples that highlight the relationship between our outdoor transportation choices and indoor air quality.

One of our indoor sensor networks installed in the Bay Area picked up on two specific outdoor events affecting indoor air quality — Bike to Work Day and the Bay Area Rapid Transit (BART) strikes in 2013.


May 9, 2013, marked the 19th anniversary of San Francisco’s Bike to Work Day; one of the largest bike to work events in the country. The success and participation in the event meant that San Francisco saw far fewer cars on the road that day than your standard work day.

However, the BART Strike, a couple months later, saw a resulting increase in the number of cars on the road as thousands of daily Bay Area public transport commuters drove to work.

The graph demonstrates elevated carbon dioxide levels during the week of the BART Strike, on July 1–2, 2013, and reduced carbon dioxide levels on Bike To Work Day on May 9, 2013.

While we can’t prove causation, there is clearly a strong relationship between major transportation patterns and indoor air quality in these two examples. By capturing these fluctuations, we’re able to gain a better understanding of how our cities live and breathe in ways that previously went unmeasured at this level of detail.

We’re excited to build on this body of knowledge through our partnership with Google Maps to measure outdoor air pollution with Aclima-equipped Street View cars. With this new layer of environmental data, we can better understand air quality as we make our way to work, school or out for a day at a nearby park.

This story shows the power of this kind of data to better connect people to our environments. Quantifying these invisible relationships gives us new eyes to see the systems that make up our world and how our choices, like transportation, impact our planet’s health and our own.