GCARE logo

Covid-19 research

We are drawing on our extensive experience in air quality to support the fight against Covid-19. In collaboration with partners around the world, we are part of the international effort making a case for the recognition of airborne transmission.


Among other projects, we are studying the impact lockdown is having on air quality in cities around the world, and investigating how different types of face mask offer protection from infection in enclosed public spaces. Read about some specific examples of our Covid-19 research.

Professor Prashant Kumar has contributed to the Royal Society’s Rapid Assistance in Modelling the Pandemic (RAMP) initiatives, including leading a subgroup on case studies of the Task 7 (environmental transmission). This group has investigated mitigation strategies of Covid-19 transmission in enclosed environments such as trains, hospitals, buses, supermarkets, restaurants, and schools and other educational settings.

Read a series of short talks on RAMP initiatives.

See the recent guidance document from RAMP, ‘The ventilation of buildings and other mitigating measures for COVID-19: a focus on winter 2020' (PDF).

paper published in May 2020 by Professor Prashant Kumar and Professor Lidia Morawska (Vice Chancellor Fellow at Surrey and Director of the International Laboratory of Air Quality and Health at Queensland University of Technology) argues that the lack of adequate ventilation in indoor environments increases the risk of airborne transmission of Covid-19.

Like many viruses, the SARS-CoV-2 virus is less than 100nm in size but expiratory droplets (from people who have coughed or sneezed) contain water, salts and other organic material, along with the virus itself. The research team note that as the water content from the droplets evaporates, the microscopic matter becomes small and light enough to stay suspended in the air, and over time, the concentration of the virus will build up, increasing the risk of infection – particularly if the air is stagnant as in many indoor environments. The study highlights that improving building ventilation is a possible route to tackling indoor transmission of the virus.

Lead author Professor Prashant Kumar said: “An improved indoor ventilation is an important step that can be taken to reduce the risk of infection. However, more must be done to recognise and understand airborne transmission of Covid-19 and similar viruses, to minimise the build-up of virus-laden air in places typically containing high densities of people.”

We are continuing our work in this area by studying and developing Covid-19 spread mitigation strategies for enclosed environments such as schools and trains.

See the full paper, ‘Could fighting airborne transmission be the next line of defence against COVID-19 spread and subsequent paper, ‘Prioritising indoor air quality in building design can mitigate future airborne viral outbreaks’.

One of the few positive impacts of the Covid-19 crisis and subsequent lockdown measures has been a dramatic reduction of harmful air pollutants across major cities in India.

recent study carried out by us and published by Sustainable Cities and Society examined the levels of harmful fine particulate matter (PM2.5) originating from vehicles and other non-vehicular sources in five Indian cities – Chennai, Delhi, Hyderabad, Kolkata, and Mumbai – and compared these results with those from other cities across the world.

The research also explored potential factors influencing differences between divergent concentration changes in different cities, as well as aerosol loadings at regional scale (see figure 1).

In addition, the team investigated the monetary value of avoided premature mortality due to reduced PM2.5 concentrations, and calculated that the reduction may have saved 630  people from premature death and $690 million in health costs in five cities across India. They pointed out that the present lockdown situation offers observational opportunities regarding potential control systems and regulations for improved urban air quality.

See our full paper, ‘Temporary reduction in fine particulate matter due to ‘anthropogenic emissions switch-off’ during COVID-19 lockdown in Indian cities.

This work builds on the NERC-funded ASAP-Delhi project (NE/P016510/1) and the EPSRC-funded INHALE project (EP/T003189/1), and our previous work on pollution strategies in Delhi and other Indian megacities, including its recent long-term assessment of ambient particulate matter and trace gases in the Delhi-NCR region.

We have collaborated with University College Dublin to conduct another study on the effects of lockdown, using both satellite data and surface measurement data to estimate air pollution across 20 cities worldwide.

We have developed a state-of-the-art filter testing rig which can evaluate the performance of different types of facemask when they are exposed to particles ranging from a few nanometers to 10 micron in size. The rig has been used to evaluate filtration and efficiency performance of different commercial, medical and handmade face masks as listed in Table 1. This experimental rig (Figure 2 and figure 3) has attracted the attention of the NHS, York Scrubs, and Innovate UK project partners (consultancy works), with a number of potential collaborations in the pipeline.

The fast particulate analyser DMS500 is capable of analysing up to 10 samples per second ranging from a few nanometers to 2.5 micron. The solenoid switching system allows the operator to automatically switch and take samples before and after sampled filters (Figure 4) in different time intervals. A snapshot of the processed data, which shows filtration performance and efficiency, size distribution, and pressure difference of a facemask filter during the test is shown in Figure 5.

The study results were recently published in the Journal of Hazardous Materials. These demonstrated size-segregated filtration efficiency, breathing resistance, and potential usage time for 11 different facemasks (four respirators, three medical, and four handmade) which were pseudo-simultaneously investigated in the submicron range.

To the best of our knowledge, no previous study has explored the potential usage time of facemasks, which is a trade-off between filter characteristics and breathing resistance. The potential usage time is a criterion that can be used optimally and safely for the disposal of facemasks in addition to other criteria such as worn-out or loose straps, presence of holes, stains on facemasks, worn thin fabric, and masks that have been washed many times.

As shown in Figure 6, although respirator masks provide the best performance (3.2 to 9.5 hours of usage time and around 97 per cent effective), medical (2.6 to 7.3 hours of usage time and around 81 per cent effective) and some handmade masks (4 to 8.8 hours and around 47 per cent effective) also provide protection but with lower usage time and effectiveness. Please note that actual usage time could be considerably higher than estimated for the wearer as it will also be impacted by factors such as leakages due to poor fitting, the wearer’s activity level and the aerosol concentration levels in their environment.

See our full paper, ‘Efficacy of facemasks in mitigating respiratory exposure to submicron aerosols’.

This work has been carried out under the framework of the MAPE Project (EPSRC project reference number 1948919). The authors acknowledge funding support from the University of Surrey, EPSRC PhD studentship and industrial collaboration with BRIZI Ltd, as well as from the EPSRC-funded COTRACE (EP/W001411/1) and COVAIR (EP/V052462/1) projects.

We have recently explored, for the first time, the nexus between in-car aerosol concentrations, ventilation, and the risk of respiratory infection. The research, which has been published in Environmental International, quantifies in-car occupants’ exposure to traffic emissions under different ventilation settings and the risk of respiratory infection. Based on this, we have proposed the most effective strategies to reduce both pollution exposure and risk of Covid-19 transmission.

The project involved monitoring aerosols (PM2.5; particulate matter < 2.5 μm and PNC; particle number concentration), CO2, and environmental conditions (temperature and relative humidity) on a 7.2km looped route three times a day (morning, afternoon, evening). This was done under three ventilation settings: windows open (WO), windows closed with air-conditioning on ambient air mode (WC-AA), and windows closed with air-conditioning on recirculation (WC-RC). By monitoring occupant exposure to CO2 levels, we were able to assess potential Covid-19 transmission as a result of co-exhalation of pathogen-laden particles by an infected occupant.

As shown in Figure 7, while the WO option exposed drivers and passengers to harmful air pollution, the fresh air could be crucial for dispersing Covid-19 particles. In addition, staying on WC-RC could expose drivers and passengers to high levels of CO2 and respiratory infection transmissions. Although both these settings provide optimal conditions for effective ventilation and pollution control, rating one over the other would be challenging since WO showed the lowest CO2 concentrations but relatively higher PNC/PM2.5 as opposed to WC-AA which showed relatively higher CO2 but lower PM2.5/PNC. A sensible selection of ventilation settings is therefore needed to balance in-car exposure to outdoor air pollution in urban areas against the risk of Covid-19 transmission. The study suggests WC-AA and WO settings are the preferred settings since the fresh air intake allows the minimisation of both exposure to air pollutants and the risk of respiratory infection transmission.

See our full paper, ‘The nexus between in-car aerosol concentrations, ventilation and the risk of respiratory infection’.

This work is supported by the Innovate UK funded project 'Pollution Guardian 2' under the Technology Strategy Board File Reference number 105725, the CO-TRACE (COvid-19 Transmission Risk Assessment Case studies - Education Establishments; EP/W001411/1) and the COVAIR (Is SARS-CoV-2 airborne and does it interact with particle pollutants?; EP/V052462/1) projects funded by the EPSRC under the Covid-19 call.

As part of the Royal Society’s RAMP initiative, we are working with rail industry companies/operators and partners from the University of Cambridge, Imperial College London and others to understand in-cabin aerosol dispersion and the risk of airborne Covid-19 transmission inside train compartments. In particular, we aim to identify how aerosols are distributed inside the compartment under different ventilation settings (on/off mode), the exposure of aerosols at different distances from the source, and how long it takes for aerosols to travel across different directions inside the cabin.

The study is designed to evaluate the distribution of fine (≤2.5µm) and coarse (≤10µm) aerosol particles at breathing height of a seated person (see figure 8 and figure 9). A fog generator was used for aerosol generation and the exhalation of aerosols from a mouth was mimicked by using a nebuliser.

In the study, which has recently been published in the Atmosphere journal, the authors undertook a series of experiments on an intercity train carriage aimed at providing a proof of concept for measuring CO2 concentrations as a proxy for exhaled breath, measuring the concentrations of different size fractions of aerosol particles released from a nebuliser, and visualising the flow patterns at cross-sections of the carriage by using a fog machine and lasers. Better understanding of these three methods will help improve our understanding of airflow behaviour and the accompanied dispersion of exhaled droplets.

We have also carried out a series of similar experiments to understand the nexus between in-car aerosol concentrations, ventilation and the risk of respiratory infection, and the efficacy of facemasks in mitigating respiratory exposure to submicron aerosols.


Woodward, H., Fan, S., Bhagat, R.K., Dadonau, M., Wykes, M.D., Martin, E., Hama, S., Tiwari, A., Dalziel, S.B., Jones, R.L., Kumar, P., Linden, P.F. 2021. Air Flow Experiments on a Train Carriage—Towards Understanding the Risk of Airborne Transmission. Atmosphere 12, 1267.

Throughout the pandemic, the transmission of Covid-19 within schools – and the hugely negative effect of school closures on children – has been a major issue globally. In the CO-TRACE project we are using a combination of field, laboratory and modelling studies to develop techniques and tools to predict the risk of airborne virus transmission in indoor school environments. Funded by EPSRC, the project is a collaboration with the University of Cambridge and Imperial College London.

Airborne infection of Covid-19 can happen through breathing recirculated air and improper airflow. Our aim in this project is to accurately represent the processes that may lead to infection in order to interpret data from hundreds of school spaces across the UK. The intention is to produce easy-to-use practical guidance and equip school staff with tools to make safe and informed decisions.

The CO-TRACE team has recently made its Covid-19 Assistance for Schools Tool (CAST) available for all. CAST helps teachers, school leaders and site managers to manage the risk of Covid-19 transmission in school environments, based on current government guidance.

The CO-TRACE project is funded by the EPSRC (EP/W001411/1) under the Covid-19 call, and complements GCARE's research on Covid-19 airborne transmissions in various environments and facemasks.

In the COVAIR project (which runs from January to December 2021) we are exploring whether tiny airborne droplets and particles can spread the COVID-19 virus in settings such as supermarkets, schools and public spaces. Funded by EPSRC, the project is a collaboration between Surrey and Imperial College London (lead partner).

The project involves collecting samples across different sites in London including hospitals, schools, care homes, offices, traffic intersections, supermarkets, train and tube stations, and buses. Samples are cultured in a high containment laboratory to see if they are able to replicate viable virus, which is a potential indication of disease caused by inhaling infectious aerosol or particles.

Professor Prashant Kumar (Director of GCARE and Co-principal Investigator in the project) said: “This project is about using our wealth of collective knowledge to identify whether we can pin down this deadly virus, track its existence in aerosols and make our urban spaces safer.

“COVAIR will look into whether the live virus can be transmitted through aerosols or pollutant particles in the air. It will build on the expertise we have developed in our current INHALE study at Imperial that aims to assess the impact of air pollution on personal health in urban environments.”

This study is supported through the UKRI’s Agile Research and Innovation Response funding to Covid-19.

Related publications

Get in contact

Contact us if you would like further information about our research activities in Covid-19, or are interested in collaborating on these projects.

Prashant Kumar profile image

Professor Prashant Kumar

Associate Dean (International), Professor and Chair in Air Quality and Health; Founding Director, Global Centre for Clean Air Research (GCARE)