Prompted by this excellent Volts podcast about indoor air quality (IAQ), which reasonably enough did not mention cars, I wanted to write about the IAQ of cars. To emphasize, it is a great epsiode. This post only has one tiny criticism of an emission.

First, the podcast is spot on that it is a travesty indicative of a failed society that decades after the invention of good filter technology to reduce the spread of disease, after the arrival of covid, after documented cognitive impacts of CO2 levels, we in America still do not take IAQ seriously for schools and students.

It’s not limited to schools. It’s also true for workplaces, government offices, homes, etc. IAQ can be even worse in poorer countries where, e.g., indoor stoves are more frequently used for heat.

We have the technology to solve IAQ and the resources needed are relatively affordable compared to the upside. If we could coordinate, improving IAQ is a no brainer. Part of that is reducing car use, especially eliminating internal combustion engine (ICE) cars, especially in cities. The pod was right to not spend its limited time discussing IAQ of cars, because the most important thing about cars for IAQ is getting rid of cars.

Outdoor air quality, usually measured according to an Air Quality Index (AQI), is also extremely important. As the pod explains America passed major policies decades ago to improve outdoor air quality because it was such a big problem. Smog was so visibly bad that it was hard for drivers to see, and of course harmed everybody across American cities breathing that air. People outside are still vulnerable to bad AQI, whether from wildfires or from tailpipes.

Car cabins are a liminal space for this purpose. Cars without a roof only have outdoor air. Other cars, with an enclosed cabin and an HVAC system of sorts, have a lot more ventilation relative to their small interior volume relative to buildings which are both larger and generally tighter. Even with recirculation mode on, cars are inherently leaky. You can tell cars are leaky by driving past a fire or something on the highway, even with windows rolled up and the fan off.

Yet most cars are enclosed and could be treated seriously for IAQ. Some people spend hours per day in a car, so improving car IAQ to them is in the same realm of importance as improving IAQ at home, work, or school.

One difference between improving the IAQ of cars versus rooms is that occupied cars are very often behind and surrounded by other cars. The first step toward improving IAQ for all of them is to reduce emissions from cars. Brake dust and tire wear are serious concerns but the primary one is tailpipe emissions of both particulates and harmful gases. Contemporary ICE vehicles already have emissions controls, e.g., catalytic converters, to try to minimize how much the exhaust can hurt people. Even better would be electrifying the fleet.

Given the vehicle traffic we have, the best way to improve IAQ for a particular car would be roughly in line with what the podcast said about buildings. Ventilate air to make sure CO2 does not build up in cabins. At the same time, use a good filter as air comes into the cabin or recirculates within the cabin. Oddly, that car company seems to have done a good job of this relative to the industry, with physically large carbon and HEPA air filters plus an option to increase fan speeds to create positive pressure in the cabin thus blocking unfiltered air from leaking in. But they idiotically call it Bioweapon Defense Mode, and since they don’t advertise at all they can’t advertised this feature either.

I wonder if larger car manufacturers have not invested more in better IAQ because it would be so hard to market. After all, if they built a better IAQ system and marketed it as an effective defense against other drivers, and especially against drivers still burning gas or diesel, it would correctly say something bad about consumers still buying ICE vehicles.

For all that American government policy strongly encourages and subsidizes driving, it’s noteworthy that IAQ for drivers is not on that agenda. That is, driving has historically been a policy goal because it enabled segregation, because it enables more monetization of transportation and the automotive industry donates accordingly, etc. Some regulation of crash risk is consistent with the car insurance industry’s best interests. But the well-being of drivers with regard to IAQ is not itself a sufficient goal to prompt action, and nobody so far has figured out how to profit from it.

My one complaint about the pod’s omission of cars concerns the discussion near the end about improving residential IAQ by reducing combustion. The rightful primary example is cooking with gas, since cooking inherently occurs in the living space. Reducing gas use in general reduces the chance of some error leading to an IAQ problem, e.g., I recently heard from a city inspector about a mistaken installation of a gas water heater resulting in exhaust going into the building until the fire department came to investigate.

But ICE vehicles can also hurt IAQ if there is attached parking. Code does not require smoke detectors in garages because of the risk of false positives from car fumes. Every time the door is opened between the living space and the garage, fumes can come in. In the most tragic scenario, leaving an engine running in a garage can even poison occupants of an attached home. Let’s minimize combustion of any sort around residential buildings.

Transit IAQ is only mentioned once, I believe mostly in the context of CO2 concentration and by implication risk of contagion across people breathing the same air. Two things I’d like to add to that. First, I am a fan of platform screen doors (PSDs) for transit for many reasons, including eliminating fall risk. One great reason for PSDs is improving the IAQ of train stations by blocking the particulates from tracks being blown into the faces of passengers on the platform. Second, let’s electrify all buses. Trolley buses where we can, batteries where we must. Transit buses and school buses. So many ICE engines are loud, hot, uncomfortable, and cause lower air quality for passengers on the bus and waiting at stops.

There’s a link between outdoor air and IAQ for CO2 that the podcast didn’t mention. Fifty years ago atmospheric CO2 was about 330 parts per million (ppm), and now it’s 425 ppm. Another way to put that is, if we have a hypothetical goal of 800 ppm for IAQ, then fifty years ago outside air was 470 ppm lower and today the outside air is only 375 ppm lower, that’s a 20% drop! As the atmospheric CO2 concentration continues to go up, the rate of ventilation in terms of cubic feet per person per minute needed to keep indoor air below 800 ppm will also go up. Greater quantity of ventilation also means more filter changes and more energy loss for heating and cooling. That’s not the worst thing about CO2 emissions but this is a very tangible impact we can already observe, if we just look at our CO2 meters and HVAC systems.