Are there medium to short-term multifaceted effects of the airborne pollutant PM2.5 determining the emergence of SARS-CoV-2 variants?

The COVID-19 pandemic has been characterised by successive outbreaks effecting large swathes of the world's populations. These waves of infection have been mainly driven by a number of more transmissible variants which appear to evade the populations' immunity gained from previous outbreaks. There appears to be a link between COVID-19 and a ubiquitous airborne pollutant called particulate matter, PM2.5. Particulate matter through a number of mechanisms, including its anthropogenic effect, appears to be associated with the incidence and the mortality related to the COVID-19 pandemic. This paper poses a number of hypotheses on the short to mediumterm mechanisms whereby PM2.5 may be party to the natural selection of SARS-CoV-2 virus, with the consequent emergence of variants.