CO₂ Levels Inside Cars in Winter: The Hidden Air Problem

You probably experienced this

You start a drive feeling alert.
After 20–30 minutes you feel:

• sleepy

• heavy eyes

• less focused

• slight headache

Most people blame:
coffee, bad sleep, or a long day.

But there is another reason — and it’s inside the car.

What actually happens inside a closed car

In winter, we naturally do three things:
• windows closed
• heater ON
• air recirculation ON

This makes the cabin comfortable, but it also turns the car into a small sealed room.

Every person exhales carbon dioxide (CO₂).
In a bedroom it accumulates slowly.
In a car it accumulates very fast because the air volume is tiny.

A typical car cabin volume is only about 2.5–3 m³.

That means just one person breathing is enough to change the air quality quickly.

Our real measurement

We placed an indoor CO₂ monitor in a normal car during a 30-minute daytime drive in winter conditions.

Starting value (fresh air): ~450 ppm

After 10 minutes: ~1,200 ppm
After 20 minutes: ~2,000 ppm
After 30 minutes: ~3,000 ppm

Nothing else changed.
No traffic jam. No passengers talking. Just normal breathing.

The driver didn’t notice the air changing — only increasing fatigue.

Why this matters for driving

High CO₂ does not remove oxygen, but it affects the brain.

At elevated levels, people commonly experience:
• reduced concentration
• slower reaction time
• drowsiness
• poorer decision-making

In other words, the brain becomes less sharp.

This is especially important during:

• highway driving

• long commutes

• late afternoon driving

• night driving

The recirculation button (the real cause)

The air recirculation mode does exactly what its name says:
it keeps reusing the same cabin air.

It heats faster and saves energy, but it also traps exhaled CO₂.

Many drivers leave recirculation ON for the entire trip during winter.

This is the main reason levels rise so quickly.

How to fix it (simple)

You don’t need to freeze inside your car.

A simple routine works:

Every 10–15 minutes:

1. turn OFF recirculation

2. bring fresh outside air for 1–2 minutes

3. then you can turn it back ON

Even a short air exchange drops CO₂ dramatically.

You may actually feel your alertness return within a few minutes.

Why you don’t notice it

CO₂ is:

• invisible

• odorless

• silent

You cannot sense it.

By the time you feel tired, levels are already high.

That is why many drivers think the problem is fatigue when the real cause is air quality.

Why we built Aeris

We created Aeris to make indoor air visible.

Most people ventilate only when they feel uncomfortable — but the body senses CO₂ very poorly.

Seeing the number change makes you ventilate at the right time instead of guessing.

Air quality is not only about comfort.
It’s also about alertness and daily well-being.

You can follow our real air quality experiments on our Instagram page.