COVID-19 following choral rehearsals. However, no direct comparison of aerosol generation from singing and speaking has been reported. Here, we measure aerosols from singing, speaking and breathing in a zero-background environment, allowing unequivocal attribution of aerosol production to specific vocalisations. Speaking and singing show steep increases in mass concentration with increase in volume (spanning a factor of 20-30 across the dynamic range measured, p<1×10 ). At the quietest volume (50 to 60 dB), neither singing (p=0. 19) or speaking (p=0.20) were significantly different to breathing. At the loudest volume (90 to 100 dB), a statistically significant difference (p<1×10 ) is observed between singing and speaking, but with singing only generating a factor of between 1.5 and 3.4 more aerosol mass. Guidelines should create recommendations based on the volume and duration of the vocalisation, the number of participants and the environment in which the activity occurs, rather than the type of vocalisation. Mitigations such as the use of amplification and increased attention to ventilation should be employed where practicable. KEYWORDS: SARS-CoV-2, COVID-19, aerosol generation, airborne transmission, aerodynamic size, singing A novel strain of a human coronavirus was first identified in late 2019, designated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and is responsible for the global outbreak termed coronavirus disease 19 (COVID-19). Pandemic status was declared on 11 March 2020 by the World Health Organisation (WHO), with in excess of 21.5 million cases and 767,000 deaths reported worldwide by 17 st August 2020. Early in the pandemic, clusters of COVID-19 were considered to have arisen in several choirs around the world. This rapidly led to many governments restricting or suspending singing. Concerns that woodwind and brass instruments might also be responsible for virus spread led to similar restrictions on the playing of wind instruments. Consequently, large sections of the cultural sector, along with religious institutions and educational establishments, were unable to rehearse and perform, resulting in profound artistic, cultural, spiritual, emotional and social impacts. The livelihoods of many performers have been jeopardised, and the viability of established institutions remains threatened. The economic impact to the United Kingdom (UK) from this sector alone has been substantial, costing the UK economy hundreds of millions in lost tax revenue, usually derived from the £32.2 billion cultural purse. Respiratory particulate matter is expelled during human exhalatory events, including breathing, speaking, coughing and sneezing. The flux generated is proportional to the amplitude of phonation in speech. These actions release a plume of material containing particles of varying size, ranging from macroscopic mucosalivary droplets originating from the oral cavity and pharynx, to microscopic aerosols released by the small airways of the lungs. Traditionally, the division between droplets, which are considered to be of sufficient mass to sediment due to gravity, and aerosols, which remain airborne, is defined arbitrarily at 5 µm diameter. However, particle composition and environmental properties like temperature, humidity and airflow influence the biophysical mechanics of the material released and the extent of transport. Droplets and airway secretions are established vectors of SARS-CoV-2, with expelled infectious material either directly inhaled by an individual in close proximity, or indirectly transmitted through contact with settled-out fomites. The role of airborne transmission by respirable aerosol particles is gaining prominence. Viral RNA has been detected in airborne samples collected both inside and outside the rooms of COVID-19 patients, and SARS-CoV-2 RNA has been reported in size-resolved aerosol distributions in two hospitals in Wuhan, China. Retrospective studies of COVID-19 clusters, including a shopping mall, a restaurant and a high-profile outbreak in an American choir group, found no direct or indirect interaction among the individuals contracting the virus, suggesting airborne transmission. SARS-CoV-2 and other viruses, including severe acute respiratory syndrome coronavirus (SARS-CoV-1) and Middle East Respiratory Syndrome coronavirus (MERS-CoV), are stable in aerosol. Infective airborne potential from human exhalation has been confirmed in other viruses, including respiratory syncytial virus, influenza and MERS-CoV. Several online reports have attempted to examine the quantities of particulate matter expelled by participants performing a range of activities including singing but have struggled to accurately quantify aerosol and droplets because of the large number of background particulates in the environment. This study is the first peer-reviewed study that explores the relative amounts of aerosols and droplets (up to 20 µm diameter) generated by a large cohort of 25 professional performers completing a range of exercises including breathing, speaking, coughing and singing in the clean air environment of an operating theatre with laminar flow ventilation. Measurements of particle number concentration alone would be insufficient to determine the total amount of viral material capable of being transmitted: the total mass of particulate matter produced may be a key factor in assessing the potential risk. Thus, measurements of particle size distributions, as well as concentration, are used to assess the mass concentration.