The paper, drawn up by Sage’s Environmental Modelling Group, said the risk of infection was high in semi-enclosed outdoor spaces such as covered seating areas, transport shelters or street market stalls.
‘Face coverings (worn correctly and of suitable quality) are likely to be most effective at reducing transmission in both indoor and outdoor settings when people are likely to be close together,” the paper said.
Face coverings should be most effective at reducing transmission in situations where people are likely to be close together, including outdoor environments where distancing may be difficult such as when queueing, Sage members said in a paper released on Friday.
Current advice on face coverings should also be strengthened to more consistently and effectively promote their proper wearing and associated good hygiene, the paper recommended.
Scientists drafted the paper on 13 January in response to concerns over the spread of the more infectious UK variant of the coronavirus, also known as B117.
The chief medical officer for England, Professor Chris Whitty, recently said the government acted too slowly in enforcing the use of masks at the start of the pandemic.
Earlier last month, Prof Whitty said there were certain outdoor environments where there could be some logic to wearing a mask.
“It’s the much longer contacts in close proximity that can still happen outdoors,” he said.
“If people for example are crowded together in a queue outdoors, if they’re really huddled together around a market stall or something, that is a risk with this virus and in that situation there might be some logic to people thinking about wearing masks.”
Other experts agreed, including Dr Shaun Fitzgerald from the University of Cambridge, who has conducted research into natural ventilation.
Dr Fitzgerald said: “If you are outdoors and there are other people around, then if the air is relatively stagnant the risk will be higher especially if you are stationary.
“If you are queuing at a market stall which is only really open to one side then this is very different from passing someone on a walk by the sea.”
The Borough Market in London last month became the first outdoor space in the UK to legally enforce the wearing of face masks. Organisers used the market’s own set of bylaws to establish a £50 fine for visitors if they do not wear a face covering in and around the stalls.