It better recirculate so it goes through the HEPA filters to capture any floating virus-embedded particles. Also air in an airliner cabin circulates laterally, not down the length of the cabin. This further limits exposure to those within the same row of seats.
Airliner air probably much cleaner than in a Walmart or pot shop:
Aircraft Cleaning and Cabin environment — Keeping you safe within our experience
Southwest Promise
Southwest Airlines aircraft are maintained in accordance with an established program aimed at providing a clean and inviting cabin environment. In addition to tidying each aircraft between flights, we spend more than six hours cleaning each aircraft every night. As of March 4, 2020, we have enhanced our overnight cleaning procedures.
Typically, we use an EPA approved, hospital-grade disinfectant in the lavatories and an interior cleaner in the cabin. Now, we are expanding the use of the hospital-grade disinfectant throughout the aircraft, and it will be used in the cabin, on elements in the flight deck, and in the lavatory. These procedures meet or exceed recommendations from the Centers of Disease Control and Prevention (CDC) and the World Health Organization (WHO).
All of our aircraft are equipped with HEPA (High-Efficiency Particulate Air) filters, which filter out airborne particles as the air onboard is recirculated with outside air. These same HEPA filters are used in many hospitals to enhance air quality within this environment.
Our aircraft are also designed with an air circulation system that mixes in fresh air from outside the plane. The HEPA filter and the air circulation system work together to provide optimum air quality while onboard a Southwest plane which, in most cases, exceeds the quality of air that can be found outdoors, as well as a typical office building or similar public venue. On average, a complete exchange of cabin air and outside air is accomplished every three minutes.
Learn how we’re protecting your health and wellness from check-in to deplaning.
https://www.southwest.com/Coronavirus/?clk=CORONAVIRUS_TA&cbid=4430033
The air system’s probably been mostly for fart handling.
HEPA filters can trap 99.95% of particles down to 0.3um. Covid-19 virus particle can be as small as 0.06 microns, and the largest are 0.14 microns.
So you want filtered air vs outside air at 30,000 feet?