Correction: Javed et al. The Potential Impact of Smog Spell on Humans’ Health Amid COVID-19 Rages. Int. J. Environ. Res. Public Health 2021, 18, 11408

There was an error in the original publication [1]. The Abstract described the relationship between smog and the COVID-19 pandemic using imprecise, cause–effect language (referring to a “worsening menace of smog” and the “occurrence of pandemic”) and framed the review’s focus as “the dubious relationship between smog and coronavirus,” stating only that lockdowns had “favored the atmosphere in some ways.”

A correction has been made to Abstract, and it should read:

Abstract: Rapid and unchecked industrialization and the combustion of fossil fuels have engendered a state of fear in urban settlements. Smog is a visible form of air pollution that arises due to the over-emissions of some primary pollutants, like volatile organic compounds (VOCs), hydrocarbons, SO₂, NO, and NO₂, which further react in the atmosphere and give rise to toxic and carcinogenic secondary smog components. Smog reduces the visibility on roads and results in road accidents and cancellation of flights. Uptake of primary and secondary pollutants of smog is responsible for several deleterious diseases, of which respiratory disorders, cardiovascular dysfunction, neurological disorders, and cancer are discussed here. Children and pregnant women are more prone to the hazards of smog. The synergistic effects of smog and COVID-19 may increase the mortality rate. Lockdown during COVID-19 had several positive effects on the environment, which will be highlighted in the article.

There was an error in the original publication. This paragraph contained a grammatical duplication (“This reduction in human activities has a positive has brought a positive impact on nature”) describing the effect of pandemic lockdowns on the environment.

A correction has been made to Section 1. Introduction, Paragraph 3, and it should read:

On the other hand, the novel coronavirus outbreak has shaken the world. It originated from Wuhan, China, and has engulfed the whole world within a year. The root cause of this pandemic, i.e., SARS-CoV-2 (severe acute respiratory syndrome coronavirus-2) is transmissible from humans to humans. It targets the respiratory tract of humans, attaches to angiotensin-converting enzyme-2 (ACE2), and down-regulates its production to cause severe respiratory illnesses. Although the mortality rate of coronavirus disease of 2019 (COVID-19) is less than 10%, together with smog, an increase in fatalities can be observed because both target the respiratory tract of humans [16]. In elderly people, coronavirus invasion is facilitated, as immune responses are weakened by age and smog [17]. Together, they may worsen the disease and can lead to hospitalization; eventually, death occurs [18], as shown in Figure 1. Studies have backed the hypothesis that components of air pollution, like nitrogen dioxide (NO₂) and particulate matter (PM) cause the excessive production of angiotensin-converting enzyme-2 (ACE2) which is the binding target for SARS-CoV-2 [19–21]. This increased production increases the susceptibility towards COVID-19. Thus, the combination of coronavirus and air pollution can exacerbate the situation. In regions like China, India, and the USA, a positive correlation is observed between COVID-19 mortality and high air pollution. This aggravates the need to control air pollution to reduce coronavirus cases where they share common hotspots [22,23]. However, there is another aspect of this pandemic. Due to the pandemic, people are locked in their houses to avoid SARS-CoV-2 infection. This reduction in human activities has had a positive impact on the environment, decreasing water, air, and noise pollution. The lockdown periods also prevented several deaths due to reductions in air pollutants [24]. The purpose of this paper is to highlight the negative aspects of the relation of smog with the current coronavirus pandemic. Along with negative aspects, positive aspects of the lockdown on air pollution are also discussed in this paper.

There was an error in the original publication. This section previously described the review’s methodology only through a short list of guiding questions (Subsection 2.1) and a single sentence referring to a simple PubMed keyword search (Subsection 2.2), without adequately describing the databases, search terms, or study selection approach used.

A correction has been made to Section 2. Research Methodology (Subsections 2.1 “Identifying the Research Question” and 2.2 “Finding and Selecting the Relevant Studies” have been removed), and it should read:

The relevant literature was primarily identified through electronic database searches including PubMed, Google Scholar, and Scopus. The search process was conducted using combinations of keywords such as “smog”, “air pollution”, “photochemical smog”, “COVID-19”, “coronavirus”, “SARS-CoV-2”, “particulate matter”, “nitrogen dioxide”, and “lockdown air quality”. Additional relevant publications were identified through manual screening of reference lists from selected articles.

This review mainly focuses on published peer-reviewed articles, reports, and authoritative sources related to the following:

Studies were selected based on their relevance to the thematic scope of the review and their contribution to understanding the relationship among smog exposure, respiratory health, and COVID-19 outcomes. Due to the narrative nature of this review, no formal inclusion/exclusion criteria, quality scoring system, or meta-analytical procedures are applied.

The collected literature was interpreted descriptively and organized into thematic sections covering smog composition, health impacts, affected populations, the relationship between air pollution and COVID-19, and the environmental effects of lockdown measures. The aim is to provide an accessible and integrative discussion of current evidence and emerging perspectives on the topic.

There was an error in the original publication. This paragraph contained a typographical error (“shrouded by a thick fig”, which should read “fog”) and a redundant duration reference (“for five days”) alongside the date range already given.

A correction has been made to Section 3. Smog, Paragraph 1, and it should read:

The 20th century marks some disastrous events related to smog. In the 1930s, the areas of Liège and Huy, alongside River Meuse, were hubs of industry in Continental Europe. After the industrial revolution, fertilizer, glass, zinc smelters, steelworks, and explosive manufacturing plants were established in these areas [25]. At the end of the year, these areas were shrouded by a thick fog (1st Dec–5th Dec). Within 3 days, hundreds of people contracted the signs and symptoms of respiratory diseases. The government was baffled completely after the deaths of 63 people. On the 6th of December, smog disappeared completely, with improvement in respiratory troubles [26].

There was an error in the original publication. The opening sentence of this paragraph contained a wording error (“Smog has affected developing as well as under-developing countries likewise”).

A correction has been made to Section 4. Some Major Smog Affected Populations, Paragraph 1, and it should read:

Smog affects both developed and underdeveloped countries alike. The air quality of any region is estimated by Air Quality Index (AQI). The higher the AQI of a region, the more pollution there is in the environment. The AQI values are compared with the units described in Figure 3. There are environmental protection agencies that work for the improvement of air quality in their regions because it affects nature as well as humans. Therefore, the implication of these standards and regulations during a pandemic is important, as they help to monitor the air quality in different regions. These standards make sure that pollutant concentrations do not cross the threshold levels, i.e., maximum permitted level (MPL), and if some have already crossed that limit, then how could we reduce their concentration to MPLs? Air pollution has become a global problem, but we can see that policies regarding control of air pollution vary from region to region. Developed regions like the United States (US) and the European Union (EU) have adopted more advanced technologies, while developing countries like India and China have just started to build their legislation regarding air pollution.

There was an error in the original publication. This paragraph contained inaccurate statistics: ambient PM_2.5 and PM₁₀ were described as having simply “become” the fourth leading cause of death in China, rather than having been identified as such in 2010; the reported peak PM_2.5 concentration during the January 2013 Beijing episode was given as “800 mg/m³”, instead of the correct 800 μg/m³; and the Beijing smog episodes were described as occurring over “multiple periods”, rather than being reported with the correct duration (six days in February 2014).

A correction has been made to Section 4.1. China, Paragraph 1, and it should read:

Air pollution has become a most concerning affair in China. Urbanization is considered the most detrimental cause of air pollution, in which rural and agricultural land is converted to urban and non-agricultural land. Moreover, natural habitats are metamorphosed into cities. The enormously increasing Chinese economy, industrialization, and urbanization come at the cost of severe air pollution, especially smog pollution [41]. After smoking, high blood pressure, and dietary risks, ambient PM_2.5 and PM₁₀ pollution was identified as the fourth leading cause of death in China in 2010 [50]. Nonetheless, the population affected by the recent events of air pollution in China is phenomenal. Each year, 350,000 to 400,000 deaths are attributed to air pollution in China [51]. Beijing faced prolonged air pollution in January 2013, during which the peak hourly concentration of ambient PM_2.5 reached 800 μg/m³ [52]. Similarly, smog persisted in Beijing for six days in February 2014. These smog spells affected not only Beijing, but also nearby cities, forcing the people to stay indoors to prevent adverse health effects [53]. The air quality index (AQI) is the unit used to measure the quality of air in a particular region. AQI between 0 and 50 is considered good, 50 to 100 is moderate, and 101 upwards is considered unhealthy. Shahecheng (156), Nantong (140), Luancheng (134), Wuda (133), Handan (132), Yangliuqing (127), Dawakou (124), Yigou (122), and Zibo (119) are currently the most polluted cities in China [54]. Being an industrial country, China has begun to endorse the policies regarding control of air pollution. Even after the implementation of the Action Plan, 2013, as a strategy to control air pollution, the levels of smog in the atmosphere are still concerning [55]. The evolution of Chinese air pollution control legislation and the standard sets for air pollutants are described in Tables 2 and 3.

There was an error in the original publication. This paragraph included an unsupported claim (“Smokeless burning facilities were announced in heavily polluted cities. Reforestation and the use of eco-friendly fuels are encouraged to reduce air pollution [59]”) citing Reference 59, which does not support this statement; this sentence and the corresponding reference have been removed (see Reference correction below).

A correction has been made to Section 4.2. United Kingdom, Paragraph 1, and it should read:

The Great Smog of London, 1952, taught the people about the long term health consequences of air pollution. In 1956, the Clean Air Act was introduced in England to cope with air pollution [58]. Despite efforts, Ashford (109), Crowborough (108), Faversham (107), Ealing (106), London (104), Shenley (104), Cambridge (103), East Ham (103), Cranbrook (102), and Lewes (102) are the most polluted cities of England [59]. The United Kingdom followed the European Union laws and standards regarding air pollution, as shown in Tables 4 and 5.

With this correction, the order of the affected in-text citations has been adjusted accordingly.

There was an error in the original publication. This paragraph incorrectly attributed cold-season smog and particulate matter pollution in California solely to “wood smoke from chimneys”, rather than to wildfire smoke and other combustion sources.

A correction has been made to Section 4.3. The USA, Paragraph 1, and it should read:

Everybody has noticed the effects of the horrible brown haze in urban communities like Shanghai, China, or New Delhi, India. However, it is observed that there are issues with air contamination in the USA as well, particularly on the off chance that you live in California, as per the American Lung Association, 2018. California’s Bay area encounters undeniable degrees of both smog and particulate matter contamination. In colder seasons, smoke from wildfires and other combustion sources can significantly contribute to particulate matter pollution and smog formation [63]. In the USA, North fork (186), Oakhurst (186), Kamiah (184), Orofino (170) Hamilton (164), Moscow (162), McCall (160), La Jolla Shores (158), Lewiston (158), and Pullman (158) are the worst cities in context to air pollution [64]. Other than these, Krasnoyarsk, Russia (169), Lima, Peru (163), Kabul, Afghanistan (156), Jakarta, Indonesia (152), Santiago, Chile (152), Tehran, Iran (108), and London, United Kingdom (104) are the topmost polluted communities of the world, according to live stats of Air quality and pollution city ranking of 2021 [65]. The US legislation related to air pollution control has evolved much and has set some standard values for pollutants, as shown in Tables 6 and 7.

There was an error in the original publication. This paragraph stated that COVID-19 “has quickly spread from its source in Wuhan City to the rest of the world,” an imprecise account of the pandemic’s early spread.

A correction has been made to Section 5. COVID-19 Pandemic, Paragraph 1, and it should read:

COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), rapidly spread worldwide [69]. According to the World Health Organization (WHO) and Center for Disease Control (CDC), around 222 M instances of COVID-19 (Coronavirus) and 4.6 M fatalities have occurred up to the 8th of September 2021. The most affected populations of the world are the USA (41 M cases), India (33 M cases), Brazil (20.9 M cases), Russia (7 M cases), the UK (7 M cases), France (6.8 M cases), Turkey (6.5 M cases), Argentina (5.2 M cases), Iran (5.1 M cases), and Colombia (4.9 M cases), with 223 countries of the world affected [70].

There was an error in the original publication. This paragraph stated that “Pneumonia-like infection was first observed in Wuhan, Hubei region, China in December 2019 in local workers of the Hunan seafood market.” This specific geographic and occupational origin claim regarding the earliest COVID-19 cases is no longer supported and has been removed.

A correction has been made to Section 5. COVID-19 Pandemic, Paragraph 2, and it should read:

Coronavirus is an RNA virus (enveloped) having a diameter of 60 nm to 140 nm. Spike-like projections are present on its surface, due to which it has a crown-like structure when observed under the electron microscope; that is why it is named Coronavirus [71]. Pneumonia-like infection was first observed in December 2019. Initially, patients faced intense acute respiratory distress syndrome (ARDS) and respiratory failure in critical stages [72]. January 7, 2020 marks the day when SARS-CoV-2 was isolated for the very first time from the throat swabs of a patient. After China, it gradually spread to Thailand, Japan, Korea, and the USA. Most first cases reported (26 out of 29) had a travel history to China. The remaining three had a meet-up with or are relatives of the other 26 patients. A study conducted by WHO members confirmed that the seafood market in China was the epidemiological source of COVID-19 [73]. Moreover, they also concluded that coronavirus spread through human-to-human contact, and no intermediary live host is involved in transmission. Coronavirus infection spreads from symptomatic people through droplets produced from coughing or sneezing, as well as from asymptomatic people [74]. The disease can also be attained by rubbing your nose or eyes after touching virus-contaminated surfaces. The stool of patients also contains the virus, resulting in contamination in the water supply [75].

There was an error in the original publication. This paragraph presented the possible link between smog and coronavirus transmission as an established fact, rather than as a subject of investigation, contained an incomplete phrase (“can remain feasible in the air for hours [97]”), and used the word “exasperated” where “exacerbated” was intended.

A correction has been made to Section 7. Amalgamation of Smog and COVID-19, Paragraph 1, and it should read:

Since COVID-19 is a respiratory disease, researchers have investigated whether smog contributes to the transmission of coronavirus [96]. Short-term exposure to elevated concentrations of air pollutants results in an increased risk of coronavirus infection. The significance of lessening air contamination is perceived under its notable effect on environmental change and its impact on wellbeing because of expanded mortality related to smog and air pollution [97]. As per recent investigations, smog appears to support the spread of coronavirus disease. As viral particles are airborne, the impact of COVID-19 may be exacerbated by smog [98]. Even though there are opposing sentiments on the transmission of SARS-CoV-2, it appears that one can obtain the disease through the air [16] because of its strength in concentrated mist [96] and the reality that the pollutant cloud and its payload (microbe-bearing droplets) can travel 7–8 m [99]. In a recent experiment, aerosols containing SARS-CoV-2 were created using three jet Collison nebulizers to mimic the aerosolized atmosphere. The viral load remained active for 3 h, even though its virulent capacity was reduced [96]. Similarly, a double hit hypothesis was also proposed initially, in which NO₂ and PM_2.5 are considered responsible for coronavirus spread [19]. Particulate matter (PM_2.5) stabilizes the exhaled droplets in the air after fusing with them. The droplet would have evaporated rapidly in the atmosphere under normal air conditions, but in high-PM concentration, PM stabilizes the droplet and reduces its diffusion coefficient, making it more transmissible. Moreover, a study conducted on mice supported the hypothesis that increased exposure to PM promoted ACE2 and transmembrane-protease serine2 (TMPRSS2) production in macrophages and angiotensin-receptor type 2 (AT2) in lung tissues. This increase made the mice more susceptible to SARS-CoV-2 [100]. The studies conducted here supported the hypothesis that regions with a high concentration of air pollution are more affected by the coronavirus. Some of these studies are listed in Table 9.

There was an error in the original publication. This paragraph specified that the Chinese government’s initial lockdown was executed “on Wuhan and encompassing urban areas,” a detail regarding the geographic scope of the lockdown that has been removed.

A correction has been made to Section 8. Impact of Lockdown on Smog, Paragraph 1, and it should read:

Since the 15th of December 2019, transmission from patients to medical care staff has happened, which shows that human-to-human transmission has occurred through close contact [110]. Most nations have forced city lockdowns also, quarantine measures to diminish transmission to manage the epidemic. Public danger correspondence exercises have been performed to improve public attention to self-insurance [111]. The Chinese government has executed a severe step-by-step lockdown as of 23 January 2020. Before long, the government of India also reported a total nationwide lockdown, from the 24th of March 2020. All industries and entertainment centers have been temporarily shut down. Domestic, as well as all international, flights have been suspended, and trains and public transport have been temporarily banned [112].

There was an error in the original publication. This paragraph incorrectly described NASA and ESA satellite data as showing “a substantial drop of 2.5µ diameter in (PM_2.5 and PM₁₀) in Beijing, China where most of the pollution comes from heating instruments in the winters and heavy industrialization,” rather than the correct finding, which concerned a drop in nitrogen dioxide (NO₂) concentrations across China when comparing the period before quarantine (1–20 January 2020) to the period during quarantine (10–25 February 2020).

A correction has been made to Section 8. Impact of Lockdown on Smog, Paragraph 2, and it should read:

The lockdowns imposed by governments all around the world have caused economical and financial instability. However, due to lockdowns, 30% reductions in air pollutants have been evident in COVID-19 epicenters like Brazil, the USA, Spain, Italy, Wuhan, according to reports of the Center for Research on Energy and Clean Air (CREA), NASA and the ESA have reported a substantial drop in nitrogen dioxide across China from before the quarantine (January 1 to 20, 2020) to during the quarantine (February 10–25, 2020) [24]. During the time of lockdown, air quality and smog conditions would be predicted to have improved in favor of the environment. Due to traffic and industrial lockdown, a fall of ~63% in the concentration of NO₂ is evident in Wuhan, China. This fall in NO₂ concentration resulted in fewer deaths of people in Wuhan (496 deaths prevented), Hubei (3368 deaths prevented), and in China overall (10,822 deaths prevented). Similarly, a shortfall of 20 µg/m³ in PM₁₀ concentration is also observed in Wuhan. However, no reduction was noticed in either SO₂ or CO concentrations because of the dependence of the country on coal-based energy plants [113].

Two references have been replaced with detailed below:

Reference 14 previously read: “Maher, A.; Abdel Rahman, M.F.; Gad, M.Z. The role of nitric oxide from neurological disease to cancer. Adv. Exp. Med. Biol. 2017, 1007, 71–88.”

It has been replaced with: “Roy, R.; D’angiulli, A. Air pollution and neurological diseases, current state highlights. Front. Neurosci. 2024, 18, 1351721.”

Reference 24 previously read: “Dutheil, F.; Navel, V.; Clinchamps, M. The Indirect Benefit on Respiratory Health From the World’s Effort to Reduce Transmission of SARS-CoV-2. Chest 2020, 158, 467–468.”

It has been replaced with: “NASA. Airborne Nitrogen Dioxide Plummets Over China. 2020. Available online: https://earthobservatory.nasa.gov/images/146362/airborne-nitrogen-dioxide-plummets-over-china (accessed on 24 April 2020).”

The authors state that the scientific conclusions are unaffected. This correction was approved by the Academic Editor. The original publication has also been updated.