A review on the effect of air pollution and exposure to PM, NO2 , O3 , SO2 , CO and heavy metals on viral respiratory infections

The ambient air pollutants that have a major role in causing respiratory diseases are particulate matter, sulfur dioxide, nitrogen dioxide, ozone, carbon monoxide, and heavy metals. In addition, respiratory infections, divided into upper respiratory tract and lower respiratory tract infection, are most commonly caused by viral agents. Thus, in light of the current COVID-19 pandemic, this review has focused on the association between exposure to general air pollution including each of the mentioned air pollutants and viral respiratory infections. The gathered evidence from the reviewed studies in this article showed that most of these air pollutants have a positive correlation with mortality, severity, transmission, inflammation, and incidence of different viral respiratory infections. Whereas, some studies found contradictory results such as non-significant and negative connections between exposure to air pollutants and viral respiratory infections, which are further discussed in this text. Therefore, following the SARS-CoV-2 outbreak, these contradictions in the reported correlation between air pollution and different aspects of viral respiratory infections must be thoroughly investigated and cleared.