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Year : 2020  |  Volume : 64  |  Issue : 6  |  Page : 132-134  

Air pollution and COVID-19: Is the connect worth its weight?

1 Director-Professor, Department of Community Medicine, University College of Medical Sciences, Delhi, India
2 Research Associate, Centre for Atmospheric Sciences, Indian Institute of Technology Delhi, Delhi, India

Date of Submission06-May-2020
Date of Decision09-May-2020
Date of Acceptance10-May-2020
Date of Web Publication2-Jun-2020

Correspondence Address:
Arun Kumar Sharma
Department of Community Medicine, University College of Medical Sciences, Dilshad Garden, Delhi - 110 095
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijph.IJPH_466_20

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Primary route of transmission of SARS-CoV-2 among humans is droplets and direct contact. Airborne transmission of this virus is not established conclusively and so is the role of airborne particulate matter. This commentary examines the existing evidence about the role of particulate matter pollutants in SARS-CoV-2 transmission. PM2.5and other small particulate matter have been shown to carry viable virus particles in the air and incriminated in spread of measles and SARS coronavirus. Empirical evidence has been provided regarding role of air pollution in accelerated transmission of SARS-CoV-2 in Italy as well as Wuhan. Lockdown-related reduction in PM2.5levels in ambient air may have contributed to reduce transmission of SARS-CoV-2. High PM2.5levels in the past might have added to SARS-CoV-2 related mortality due to air pollution relate comorbidities. Post-lockdown increase in PM2.5levels may accelerate covid-19 transmission and can add to the burden of COVID-19 morbidity and mortality.

Keywords: Air pollution, air quality, lockdown, PM2.5, SARS-CoV-2

How to cite this article:
Sharma AK, Balyan P. Air pollution and COVID-19: Is the connect worth its weight?. Indian J Public Health 2020;64, Suppl S2:132-4

How to cite this URL:
Sharma AK, Balyan P. Air pollution and COVID-19: Is the connect worth its weight?. Indian J Public Health [serial online] 2020 [cited 2022 May 25];64, Suppl S2:132-4. Available from:

The primary routes of transmission of SARS-CoV-2 among humans are established to be droplets and direct contact. An epidemic model based only on respiratory droplets and close contact could not fully explain the regional differences in the spreading of the COVID-19.[1],[2] The possibility of airborne transmission has been debated. The role of particulate matter (PM) in air in transmission of this virus is also not established. However, it is worth exploring and understanding specially when lockdown is not viable anymore and the world is ready to get back to business as usual.

COVID-19 pandemic has spread across 210 nations and territories, thus covering all types of human habitations across the globe. It originated in Wuhan, the capital of Hubei province in China.[3] Air quality in Wuhan is one of the worst in China. In 2019, on 280 days, the PM2.5 levels had been at least 100 μg/m3 and was above 200 μg/m3 on another 40 days in the same year.[4] The COVID-19 spread fast in Wuhan as number of cases jumped from 3 in the last week of December 2019 to 50,333 on April 16, 2020.

A number of studies have shown that airborne transmission route could spread a virus farther than close contact with infected people. It has also been demonstrated that it can reach long distances through aerosolization.[5],[6] The possibility of airborne transmission was suggested in case of SARS outbreak in Amoy Garden housing complex in Hong Kong by Yu et al.[7] The presence of virus particles have been demonstrated on PM2.5 and PM10 by Cao et al. in a sample of air collected from Beijing during a severe smog event.[8] Activities resulting in aerosol generation increased the chances of spread of SARS coronavirus.[9] Air pollution is considered as one of the accelerator of COVID-19 transmission, because PM can act as a carrier of viable virus particles and can spread it beyond 2 meters' distance. Van Doremalen also demonstrated that SARS-CoV-2 remained viable and infectious in aerosols throughout the 3 h duration of an experiment.[10] Chen et al. showed that every 10 μg/m3 increase in PM2.5 is associated with significantly increased measles incidence.[11]

Some researchers have attributed the high number of cases in Wuhan to airborne transmission of the coronavirus. From a study in two hospitals in Wuhan, Liu et al.[12] concluded that SARS-CoV-2 can be airborne in gathering of crowds with asymptomatic carriers and Santarpia et al.[13] confirmed presence of airborne SARS-CoV-2 in air sampled at the Nebraska University Hospital in USA.

Cai et al. after analysing the spread of infection among a cluster of COVID-19 cases in a mall in Wenzhou opined that virus aerosolization in closed spaces could be one of the methods of transmission.[1] Experimentally, it has been seen that expelled air contains droplet particles as well as aerosolised particles of ultra-small dimensions, that remain airborne for a long time and travel long distances. There is no reason not to believe that these particles can remain loaded with the virus.

Setti et al. studied the role of air pollution in spread of SARS-CoV-2 in Italy. The study noted that the Lombardy and Po Valley region in northern Italy has highest number of COVID-19 cases and most polluted air in the country. Based on univariate analysis, it was established that PM10 value exceedances (>50 μg/m3) were a significant predictor of SARS-CoV-2 infection while comparing the infection and air pollution data of 43 cities with higher and 67 cities with lower PM10 concentrations.[2]

To take the evidence to the level of biological plausibility and beyond empirical construct, comparison has been made between 55 Italian province capitals and it has been conclusively demonstrated that number of cases were higher in more polluted cities.[14] This is in sync with the findings of the Wuhan study.[12] Both the places were put under strict lockdown after the outbreak. The lock down not only affected through social distancing and isolation of the COVID-19 cases from the unaffected population but also affected the air pollution significantly. In Wuhan PM2.5 levels were reduced by 44%.[15] This certainly is expected to have synergistic effect in bringing down the infection rate. However, in the absence of systematic epidemiological research, all of the Hill's criteria for causality[16] cannot be satisfied and role of PM concentration cannot be established conclusively. Nevertheless, this needs to be researched. In contrast, Sweden is a country that has not enforced any lockdown. It has one of the best PM2.5 levels in the world. Out of 127 days in 2020, only on 18 days PM2.5 levels were above 25 μg/m3. Moreover, the number of COVID-19 cases were only 22,721 and 2769 deaths.[17] Of course it may only be an ecological evidence.

In Indian context, cities such as Delhi and Mumbai have shown a reduction of 60% and 34% in PM2.5 levels respectively during the lockdown from March 23, 2020, to April 13, 2020. Other high density population hubs such as NOIDA, Gurugram, and Jaipur have shown more than 50% reduction in PM2.5 levels from the pre-lockdown period to the first lockdown period (source: Atmos Real Time Air Quality, Respirer Living Sciences, Mumbai, India.)

Another mechanism by which pollution may influence the course of COVID-19 pandemic is the role of air pollution in comorbid conditions. Comorbidities, such as hypertension, diabetes, and coronary artery diseases are exacerbated by air pollution. COPD and other chronic respiratory morbidities are worsened in high pollution states. Both the above conditions are associated with poor prognosis in COVID-19 patients. The study by Xiao et al. looked at long-term exposure to PM2.5 from 2000 to 2016 across 3080 counties covering 98% population of the USA. The study estimated PM2.5 exposure levels on a monthly basis at 0.01° × 0.01° grid resolution across the entire continental United States by combining satellite, modelled and monitored PM2.5 data in a geographically weighted regression. The analyses adjusted for 16 potential confounders. They found that increase of only 1 μg/m3 in long term average PM2.5 is associated with a statistically significant increase of 15% in the COVID-19 death rate.[18] The interpretation can have a historical significance only. Neither does it help us model or forecast the mortality outcomes in future because the effect had been of long-term exposure and related to chronic ailments of prolonged standing. Given that COVID-19 is an acute emergency, such long-term scenarios are unrealistic in future. It cannot be extrapolated to infer that reduction of PM2.5 during lockdown is going to reduce COVID-19 mortality at the rate of 15% per microgram reduction in PM2.5 levels. However, this is another topic for research to see if reduction in PM2.5 has reduced air pollution related mortality or not.

One caveat in such bivariate analysis is that the mechanism of causation is far more complex and it is always an interplay of other known contributing factors such as social distancing, use of masks and other PPEs, isolation, quarantine, hand hygiene and sanitization at micro as well as macro level besides the air pollution component. Hence, the net outcome will be guided by each component and not any one isolated condition.

It can be concluded that air pollution reduction will reduce COVID-19 infection rate, case fatality rate besides reducing the other morbidity and mortality attributable to air pollution. On a philosophical note, there has been buzz about earth healing itself, nature regaining it is lost ground on the planet and certainly human beings appreciating these positive changes in the environment, but the question remains, will this COVID-19 outbreak be able to teach us a permanent lesson and make us more responsible toward preserving the nature on our planet and let it be more livable or the wave of this good outcome will die down with the dying of COVID-19 and back to business as usual!

Most of the nations are contemplating to lift the lock down. As and when it happens, with return of vehicles on the roads, re-ignition of industrial boilers and rising demand of energy across the world, the PM2.5 and PM10 levels will start heading north toward the prelockdown levels. Asymptomatic coronavirus careers and mild symptomatic cases will be out on the streets. This combined with raised dust, PM10 and PM2.5 levels in ambient air will potentially increase the SARS-CoV-2 transmission multi-fold. This will also start adversely affecting the already compromised immunity of persons above 60 years of age and living with chronic respiratory illnesses and other comorbidities, making them more vulnerable to being infected with SARS-CoV-2; thereby undermining the gains of lock down and a risk of a more ominous second wave of infection and deaths. And to avoid that, stricter implementation of existing prevention and control measures such as using mask, social distancing, hand washing, and improved hygiene practices will be the only tools till vaccines and therapeutic drugs are discovered.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

Cai J, Sun W, Huang J, Gamber M, Wu J, He G. Indirect virus transmission in cluster of COVID-19 cases, Wenzhou, China, 2020. Emerg Infect Dis 2020; Online, ahead of print.  Back to cited text no. 1
Setti L, Passarini F, Gennaro GD, Barbieri P, Perrone MG, Piazzalunga A, et al. The potential role of particulate matter in the spreading of COVID-19 in Northern Italy:First evidence-based research hypotheses. MedRxiv preprint. [].  Back to cited text no. 2
Shereen MA, Khan S, Kazmi A, Bashir N, Siddique R. COVID-19 infection: Origin, transmission, and characteristics of human coronaviruses. J Adv Res 2020;24:91-8.  Back to cited text no. 3
Wuhan Air Pollution: Air Quality Historical Data. World Air Quality (Index). Available from: [Last accessed on 2020 May 06].  Back to cited text no. 4
Andersen GL, Frisch AS, Kellogg CA, Levetin E, Lighthart B, Paterno D. Aeromicrobiology/Air Quality in Encyclopedia of Microbiology. 3rd ed. Academic Press, Oxford; 2009. p. 11-26.  Back to cited text no. 5
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Yu IT, Li Y, Wong TW, Tam W, Chan AT, Lee JH, et al. Evidence of airborne transmission of the severe acute respiratory syndrome virus. N Engl J Med 2004;350:1731-9.  Back to cited text no. 7
Cao C, Jiang W, Wang B, Fang J, Lang J, Tian G, et al. Inhalable microorganisms in Beijing's PM2.5 and PM10 pollutants during a severe smog event. Environ Sci Technol 2014;48:1499-507.  Back to cited text no. 8
Paules CI, Marston HD, Fauci AS. Coronavirus infections – More than just the common cold. JAMA 2020;323:707-8.  Back to cited text no. 9
van Doremalen N, Morris DH, Holbrook MG, Gamble A, Williamson BN, Tamin A, et al. Aerosol and surface stability of SARS-Cov-2 as compared with SARS-Cov-1. N Engl J Med 2020;382:1564-7.  Back to cited text no. 10
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Liu Y, Ning Z, Chen Y, Guo M, Liu Y, Gali NK, et al. Aerodynamic characteristics and RNA concentration of SARS-CoV-2 aerosol in Wuhan Hospitals during COVID-19 outbreak. Preprint Bio XRiv 2020; BioRxiv preprint.  Back to cited text no. 12
Santarpia JL, Rivera DN, Herrera V, Morwitzer JM, Creager H, Santarpia GW, et al. Transmission potential of SARS-CoV-2 in viral shedding observed at the University of Nebraska Medical Center. 2020; MedRxiv preprint.  Back to cited text no. 13
Coccia M. Factors determining the diffusion of COVID-19 and suggested strategy to prevent future accelerated viral infectivity similar to COVID. Sci Total Environ 2020;138474. Online, ahead of print.  Back to cited text no. 14
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Xiao W, Nethery RC, Sabath MB, Braun D, Dominici F. Exposure to air pollution and COVID-19 mortality in the United States: A nationwide cross-sectional study. medRxiv 2020; MedRxiv preprint.  Back to cited text no. 18

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