Air quality is neither a stable material phenomenon, nor form of knowledge. This was made clear upon the arrival of COVID-19 in school classrooms when humans emerged as the primary source of poor indoor air quality (IAQ), and a host of new devices were placed into schools to monitor and clean IAQ. In this paper we examine this instability as it had consequences within a research-business project attempting to measure IAQ and assess the effectiveness of an air cleaning device in school classrooms pre- and post- the emergence of COVID-19. Using a ‘near’ Actor-Network Theory analytical framework we focus on how a network of ‘science in action’ became re-assembled to COVID-19. Drawing on IAQ data that we collected, government and industry statements and reports, and the direct involvement of the lead author using both reflexive and relational ethnographic approaches, we show how our IAQ measurements, combined with other material inscriptions, were powerful actants that changed the relationship between the air indoors and outdoors. We bring Maria Puig de la Bellacasa’s concept of ‘matters of care’ into conversation with the project detailing how changing socio-material circumstances led to a more active role to reconfigure classroom IAQ, and how we might better care for IAQ in the future. We also relate our project to the wider – and ongoing – process of reassembling IAQ, asking how this might relate to questions of inequalities and responsibilities.