Solar heating to inactivate thermal-sensitive pathogenic microorganisms in vehicles: application to COVID-19.

Disinfection is a common practice to inhibit pathogens, yet success is limited by microbial adaptation and our poor knowledge of viral transmission, notably in the current COVID-19 pandemic. There is a need for alternative disinfection strategies and techniques that are adapted to the actual behavior of humans living in densely populated mega-cities. Here, high public circulation in shared passenger vehicles such as taxis, buses and personal cars represents a major risk of viral transmission due to confined space and commonly touched surfaces. Actual regulatory guidelines are not fully successful because they rely both on passengers' willingness to wear face masks and on drivers' willingness to disinfect cars after each shift or each ride with symptomatic individuals. Here we propose that passive solar heating, a sustainable technique that has been used in agronomy to kill weeds and soil pathogens, could inactivate the virus in vehicles during warm-to-hot weather within few minutes to half an hour at 50-60 °C. We measured temperatures in a white compact-size sedan left in a parking lot under direct sunlight. Air temperatures increased from 30 to 42-49 °C after 30 min and then reached a plateau at 52-57 °C after 90 min. Temperatures were about 3 °C higher in front versus back of the car and about 5 °C higher at face height compared to knee height. Since COVID-19 is inactivated in 30 min at 56 °C, our findings confirm that hot air generated passively by solar heating in enclosed spaces is a promising strategy of disinfection with benefits of no added costs, chemicals or worktime. Though this technique appears limited to hot climate, possible heating systems that work during parking time might be developed by vehicle makers to extend the technique to cold climates.