Can free floating lone SARS-CoV-2 virus cause infections?

You’re saying that mucus stops viral transmission by binding with the virus, and preventing them from impacting epithelial cells when inhaled by a future host. But what if it’s a free floating virus, not in a mucus aerosol? Just a lone virus, no protective mucus.  

Free floating virus don’t appear to be able to cause human respiratory infections, either at all, or only as a very unusual event. The mechanism for this is unclear, it may be that a certain concentration of virus is needed to cause an infection, or perhaps free floating virus don’t survive the dehydrating process between hosts, or something else entirely. There’s a need for observation studies here.

What we do know is different sized particles tend to impact the respiratory tract in different places. In general terms, the smaller they are, the deep into the lungs they can penetrate. You can observe this happening here:

Most respiratory infections including COVID-19 begin in the upper respiratory tract, which implies a minimum size of infectious aerosol of at least around ~5 microns, assuming a solid spherical shape with the density of water.

If free floating virus did cause respiratory tract infection most infections would begin in the lower respiratory tract which would naturally be me vulnerable as it has a vastly larger surface area and a much thinner layer of protective mucus.

The mucus aerosol appears to be integral to infection as well as transmission immunity.