What role does smog play in spreading the coronavirus?

High levels of air pollution, including particulate matter Pm2.5 and Pm10, are statistically associated with a greater number of Covid-19 cases. The particulate may contain traces of viruses, although it is not known if and how much they can infect, but it does not carry it more through the air than the wind does.

(photo: Nello Giambi via Getty Images) The relationship between air pollution and infection is discussed in the Covid-19 pandemic, with hypotheses sometimes conflicting. Does city smog promote contagion? And can particulate matter become a vehicle of the virus through the air? These and other questions are at the center of researchers' attention. And studies on two research fronts flock. The first concerns the possibility that air pollution may play a role in the contagion or in the worsening of symptoms. Some current and previous pandemic tests, obtained on other pathologies, including respiratory diseases but not only, show that at high levels of air pollution correspond to an increased risk of infection or more serious forms. The other study is to understand if smog can favor the propagation of coronavirus by transporting it through the air. If on the one hand traces of the viral RNA of Sars-Cov-2 have been found on atmospheric particulate matter, on the other hand the evidence collected so far does not support the hypothesis that the particulate matter carries the virus remotely. This is why and what we know today of the relationship between air pollution and Covid-19 infection.

particulate matter contains traces of rna of Sars-Cov-2

In Italy it all began when the Italian Society of environmental medicine (Sima) has published a position paper that highlighted the potential link between high levels of particulate matter in the north of Italy of the country and the most number of infected, just in the Plain of the Po and in the regions of the north. The survey was preliminary and had several limitations. Later, some researchers of Sima, along with other colleagues, coordinated by Leonardo Setti , have published research on Environmental Research which shows that in Bergamo , a town heavily affected by Covid-19, in the midst of the epidemic were no traces of coronavirus on 16% – almost 1 in 5 – of collected samples of atmospheric particulate. “The study is interesting,” commented Daniele Contini , researcher at the Institute of atmospheric sciences and climate of Cnr, is not involved in the investigation, which from time to time is concerned with the issue, “because it shows that the virus is detectable in the air, which may be used as the indicator of an outbreak. However, we must point out, as do the authors that has not been measured the concentration of viral rna is needed to understand whether this is in concentrations that are significant or insignificant and whether it is active and infectious” . Have found traces of viral rna on the Pm2,5 and Pm10 , in fact, does not imply that this is intact and able to infect if inhaled.

But not the transports

“Also the result obtained in Bergamo does not indicate that the particulate matter and to encourage a greater spread of the virus by transporting it through the air at a distance of tens or hundreds of meters,” remarked Contini. “This is also because the Sars-Cov-2, like many other pathogens and chemicals – think of the toxic arsenic that can be present in traces in the air – are transported and carried by the winds or by currents of air and do not need a support material, an intermediate, of a vector, as in this case, the particulate matter” . In short, admitted that the virus can travel in the open air in a quantity not negligible – everything to prove, since the evidence indicates otherwise – does not rely on air pollution to be able to do that.

Even if the virus is carried by the air, then, is easily degraded by various factors, including weathering, " explains Contini. “We consider that in conditions protected, such as those of the laboratory” , specifies the expert, “ the virus suspended in the air, survives from 1 to 3 hours . Outdoors the situation is very different: in addition to moving you have to consider several elements, including weathering” . For example, the ultraviolet radiation , especially Uvc rays but also Uva – which represent 99% of the Uv radiation reaching the earth's surface – and Uvb (absorbed 95% of the atmosphere) can damage and destroy the virus. “This of course does not mean that exposing yourself to the sun is immune from the contagion, which occurs via the air primarily by direct contact between people and with the hands” , underlines the expert, “but in outdoor environments the path of the live virus and infectious may not be very long . Other elements that may contribute, although to a lesser extent, to degrade, are the high temperatures and low humidity : this is because the presence of moisture is, therefore, a liquid part, can help the virus to remain intact” .

The virus is transmitted via aerosols?

so Far, studies have shown that the transmission of the virus through aerosols in the open air is found to be negligible , even if the topic is still discussed, even by the Who, and several researchers around the world believe that instead needs to give a greater weight. “Notwithstanding that, to understand what is the weight of this type of transmission remains complicated, especially outdoors, to the exclusion of

any areas of the gathering,” stresses Contini, “the research not only in italy (here, for example, conduct in Wuhan and in the preprint) show that outdoor concentrations of viral rna are very low and it is unlikely, at least for the actual trials, this route of transmission is the basis of a mechanism of contagion was significant in the outdoor” . The scientist together with the group of the Cnr is conducting two surveys on this subject, through a computational model that reproduces the situation of Milan and Bergamo, and another through the analysis of air samples collected in the middle of the epidemic, both in the north and in the south of Italy. “In the first study, which is based on models and not on sampling the environment” , stresses Contini, “even assuming that a good chunk of the population, equal to 10%, is infected , the concentrations of viral rna in the air remain very low” .

If the risk of transmission via aersol outdoor is very low, unlike in the case of indoor environments , where this infection is more likely, especially if there are several infected persons. “The review of the available studies – says Contini – indicates that we need to pay attention to environments such as hospitals, transport, shopping centres and all those places are closed to a high frequency where the presence of one or more persons positive to the new coronavirus can promote other infections” .

The smog, however, increases the risk of Covid-19

If the smog does not carry and contains more of the virus, it's bad for the health of the lungs and can increase in some individuals who are already predisposed or susceptible, for example patients with chronic respiratory diseases such as Copd, the risk of infection with new coronavirus, or a deterioration – a factor that has nothing to do with the fact that the virus is present on the particulate. To support him is a large group of Italian experts, of the Italian Network of environment and health : according to the specialists the underlying assumption is that a high concentration of particulate matter ( Pm10, Pm2,5 ) make long-term the respiratory system more vulnerable to infection and to complications of the disease from coronavirus. This applies mainly to the prolonged exposure time, while for the short-term there is insufficient evidence – so the effect is even more visible in the elderly population. But this is not surprising, experts explain: it is not a coincidence that the Pm2,5 cause, each year, 2.9 million premature deaths, according to the report the State of the Global Air report 2019 all over the world and are among the major risk factors for health after diet, smoking, hypertension and diabetes . “Still though,” stresses Contini, “it is not known what the real contribution of air pollution in determining the infection Covid-19, and in a worsening of symptoms and call it, is not simple, also considering the presence of local factors, such as the high population density, uses and habits, and the presence, in a given area, a tourist attraction or a professional , with a greater number of movements and social interactions, for example, if we think of the Italy of the north” .

In any case, the hypothesis that particulate matter, carbon monoxide, nitrogen dioxide and other pollutants have a role is possible. And it is not a case that not only the study of Italian in Bergamo, but also other research, such as this one conducted in China by Nanjing University , detect a statistical association also significant between the levels of some air pollutants, particulate matter in the first place, and the incidence of cases of Covid-19. “There is a statistical correlation, not a causal cause-and-effect ” , stresses Contini. “ Also, it is always the speech to which the individual risk can increase for exposures protracted over time. For short-term exposures there is insufficient evidence of a bond and this kind of studies are usually conducted for acute episodes such as cardiovascular events . For infectious diseases is the most difficult, given that it is more complicated to extract a relationship in the short term for various reasons, including the fact that the onset is not immediate, immediately after entering into contact with the virus” .