Competing interests: We have read and understood BMJ policy on declaration of interests and declare the following: SF is a co-investigator on the UKRI AIRBODS research programme, CN is principle investigator on the UKRI TRACK, Breathing Cities and HECOIRA projects and co-investigator on the NIHR Contact study. SP is co-investigator on the UKRI TRACK project. HR, SF, AS, CN were on the working group for the Royal Academy of Engineering Infection Resilient Environments report. CN was on the working group for the Academy of Medical Sciences reports on covid in 2020 and 2021. WST is employed by The BMJ but was not involved in, or privy to, any aspects of editorial decision making for this article or the accompanying paper in BMJ Open.