Many drivers have not used the correct air intake mode
Sharing with reporters, automotive engineer Le Van Tach said that during the maintenance and repair of cars, he found that many car owners did not correctly understand the functions of the intake and outtake modes.
According to Mr. Tach, some people are worried that dust will enter the air conditioning system, so they block the external air intake. Some drivers default to using indoor ventilation because they believe that this mode helps the cabin cool down quickly and limits dust and unpleasant odors from outside.
When the air vent is turned on, the air conditioning system circulates most of the air available in the cabin. This mode is often used when quick cooling is needed or when the car passes through areas with a lot of smoke, dust and unpleasant odors.
Meanwhile, the external air intake mode brings air from the outside through the ventilation system into the cabin, helping to increase the amount of new air in the car. However, which mode to use depends on weather conditions, air quality outside and traffic conditions.
Mr. Tach advised drivers not to maintain continuous inertia throughout long journeys, especially when the car is carrying many people. Drivers can switch to inertia for a suitable period of time to increase air exchange in the cabin.
CO2 can increase when cars take in prolonged inertia
The car cabin is not a completely closed compartment. However, when using air circulation mode, the amount of new air brought in from the outside is limited, while people in the car continuously emit CO2 through the respiratory process.
Research entitled Carbon dioxide accumulation inside vehicles: The effect of ventilation and driving conditions by N. Hudda and S.A. Fruin, published in the journal Science of the Total Environment in 2018, shows that ventilation is the factor that has the greatest impact on CO2 accumulation in the cabin.
According to research, when cars use indoor ventilation mode, CO2 can increase higher, especially on long trips, cars carrying many people or moving in congested conditions. However, for most trips with one or two people and an average travel time of about 26 minutes, CO2 concentrations usually do not exceed 2,500 ppm. The author group recommends that cars carrying many people or traveling for long periods should periodically turn off circulatory mode or add extra air to the cabin.
Another study called In-vehicle carbon dioxide and adverse effects: An air filtration-based intervention study, published in the same journal in 2020, was conducted with 84 healthy people driving for about an hour.
The results recorded that CO2 levels in the tank were related to increased sleepiness in participants. When the CO2 filter system worked, the CO2 concentration decreased and the recorded sleepiness level also changed. The study concluded that the filter system could reduce CO2 in the cabin and adjust the observed effects on heart rate, blood pressure and sleepiness while driving.
The above results do not mean that every case of catching air makes the driver sleepy. The CO2 level in the cabin also depends on the number of people in the car, travel time, ventilation mode, travel speed and characteristics of each vehicle.
In the Hyundai Tucson 2025 user manual, the manufacturer also warned that maintaining the air conditioning system in air-intake mode can cause drowsiness, impaired alertness and affect vehicle control. Hyundai recommends switching to intake air when driving; after the cabin is cool enough, users should switch from air circulation to intake air outside.
Currently, there is no fixed time period applied to all types of vehicles regarding how long to switch to external air. Users should refer to the manufacturer's instructions and proactively adjust according to the number of people in the car, journey length as well as external air quality.
In case you feel sleepy or distracted, drivers should not just switch to air conditioning and then continue moving. The US National Highway Traffic Safety Administration recommends that drivers stop their vehicles in a safe place and rest when signs of sleepiness appear.
