The growing impact of air quality on lung-related illness: a narrative review

Abstract

Background and Objective

Poor air quality can be harmful to human well-being. There are a variety of respiratory disorders associated with toxins present within the atmosphere, such as bronchitis and asthma, which eventually lead to heart or lung complications over time. Fine particles like particulate matter 2.5 (PM2.5) accumulate in the small airways of the lung. These irritants can cause epigenetic modifications in gene regulation, leading to changes responsible for both benign and malignant lung diseases. In this review we will discuss known associations between environmental factors and pulmonary complications, consider preventative measures and offer further areas for future investigation. This review presents a summary of the literature outlining the current work done on air quality and its effects on lung-related illnesses. We discuss regional differences in air quality and consider the causes, such as manufacturing, traffic density, increase in fuel usage and natural events. We further explore disparities based on geography, race, and other social determinants.

Methods

A comprehensive literature review was performed using keywords related to air quality, pollution and lung disease within the PubMed database as well as MEDLINE and Google Scholar.

Key Content and Findings

The Clean Air Act of 1970 marked an essential transition for air quality improvement. The legislation led to decreased emissions and control measures to address atmosphere contamination. Despite these actions, poor atmospheric conditions still persist today and have become an ongoing issue. These poor conditions affect individuals living in metropolitan areas more significantly than suburban or rural areas. Pollution from industrial operations and transportation vehicles have led to increased emission outputs recently. Climate change further aggravates air quality problems by raising pollutant and allergen concentrations. The detrimental consequences of poor air quality include increased incidence of disease processes like asthma, chronic obstructive pulmonary disease (COPD) and lung cancer. To keep up with the well-being of people globally, it is important that actions be taken to battle contamination in the climate so its impact on public health can be limited.

Conclusions

Poor air quality and recent worsening of industrial emissions have had a negative impact on lung-related illnesses. Future mitigation strategies should be taken to reduce pollution and treat diseases earlier in their course. Some of these strategies include more reliance on alternative energy sources, creation of mass transit systems and increased rates of recycling.

Introduction

The study of ambient air quality and its deleterious effects on human health have been brought to the forefront in recent times. Poor air quality has been tied to multiple respiratory diseases, ranging from asthma and bronchitis to long-term heart and lung diseases (1-6). Outdoor air pollution constitutes one of the leading global health risks. Fine particulate matter (PM2.5) describes particles with an aerodynamic diameter of less than 2.5 mm. Environmental pollutants have been identified as being among the top five causes of death globally (7). In addition, PM2.5 has been demonstrated to cause epigenetic and micro-environmental alterations in the lung and is linked to the development of lung cancer (8,9). Radon gas and smoke from burning domestic fuels further elevate lung cancer risk when exposed over extended periods of time (10). We present a narrative review of the literature outlining the current work done on ambient air quality and lung diseases. We present this article in accordance with the Narrative Review reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-23-544/rc).

Methods

We reviewed all articles using terms via PubMed, MEDLINE, and Google Scholar. The eligible studies were searched from 1 March 1992 to 1 March 2023. Our search queried “Air quality and respiratory”, “air quality and lung”, “pollution and respiratory” and “pollution [and] lung”. Our search was limited to retrospective studies, meta-analyses, abstracts and reviews (Table 1). Reviews and meta-analyses were included only for cross-reference check. After removal of duplicates and studies that were not relevant, a total of 1,320 studies remained. These studies were reviewed, and in total 68 references were included in this narrative (Figure 1).

Table 1. The search strategy summary.

Items	Specification
Date of search	March 15, 2023
Databases and other sources searched	PubMed, MEDLINE, Google Scholar
Search terms used	“Air quality and respiratory”, “Air quality and lung”, “Pollution and respiratory”, “Pollution and lung”
Timeframe	1992–2023
Inclusion criteria	Retrospective studies, meta-analyses, abstracts and reviews
Selection process	All authors participated in the selection process. Consensus was obtained through group discussion

Figure 1.

PRISMA graph to show method of selection process.

Discussion

Air quality over time

The Clean Air Act of 1970 (CAA) has undoubtedly had a beneficial impact on air quality in the United States, setting national standards for pollution levels and requiring industries and transportation sources to lessen their emissions. The CAA also included a grant program that provided local and state governments the necessary funds to collaborate with the Environmental Protection Agency (EPA) in improving air quality (11). According to EPA data, concentrations of six major pollutants such as ozone, carbon monoxide, lead, PM, nitrogen dioxide (NO₂) and sulfur dioxide (SO₂) have all declined since this legislation was passed decades ago. These reductions range between 70 to 90 percent depending on location. This reduction was due mainly more efficient emission control systems and cleaner fuel alternatives (12). Nonetheless, warmer temperatures have led to an increase in pollutant levels and accumulation in toxic smoke from wildfires (13,14). While certain restrictions have been imposed on automobile emissions and factories, they still constitute some of the most common sources of contamination.

Regional differences in air quality

Urban vs. suburban

Urban air quality can be impacted by a wide range of causes, from industrial emissions to vehicle exhaust and construction activities. Structures in these areas, such as buildings and infrastructure, trap pollutants and further worsen air quality. This problem has been intensified by increased population densities in cities compared with their suburban or rural counterparts (15,16). In addition, industrial production and transportation are more prevalent in cities and further contribute to air pollution. Suburban air quality is typically better than urban areas due to lower population density and fewer sources of pollution (17). Nevertheless, emissions from industrial sites in the vicinity, vehicle exhausts from nearby roads and highways and topography may influence pollutant concentrations and PM2.5 levels in suburban areas (18).

Different parts of the United States

The United States is composed of a wide array of air quality levels, from highly polluted urban areas to very clean rural regions. The northeastern region of the United States is a densely populated area with numerous industrial and transportation sources that contribute to air pollution. Cities such as New York, Boston and Philadelphia face some of the most serious challenges in dealing with elevated PM2.5, nitric oxide (NO₂) and ozone levels (19-21). Major cities in the southeast, including Atlanta, Charlotte, and Houston, are heavily populated and have a warm, humid climate that often contributes to air pollution (22). These cities experience high levels of ozone, PM2.5 and NO₂ from industrial activities and transportation sources. The Midwest region of the United States has a powerful agricultural and industrial infrastructure which unfortunately produces copious amounts of air pollution, particularly PM2.5 and NO₂ (23). Major cities like Chicago, St. Louis, and Detroit can be especially vulnerable to adverse levels of these pollutants in the summer. The western region of the United States has been marred by alarming concentrations of air pollutants, such as PM2.5, NO₂ and ozone. These contaminants are mainly derived from vehicular exhaust emissions, industries, and wildfires in cities like Los Angeles, San Francisco, and Seattle. These contaminants pose a serious threat to both public health and environmental integrity (24).

Different parts of world

The results of air pollutants have extended beyond certain regions and had a global impact. The Canadian Air and Precipitation Monitoring Network (CAPMoN) has observed a marked improvement in air quality in Canadian cities during the past two decades, in spite of ongoing challenges from industrial emissions, transportation-associated pollutants and wildfires. Comparable improvements have been made in air quality throughout Europe, mostly from regulations passed by various governments. These regulations were enacted to curb emissions from commercial sites, automobiles and energy production sources. According to the European Environment Agency, there have been significant reductions in PM2.5 and NO₂ concentrations throughout Europe. Urban sectors generally face higher pollution rates than rural localities, however, mainly in cities where traffic density is considerable (25). The Health Effects Institute’s 2020 State of Global Air Report confirmed that outdoor air pollutants led to 4.5 million fatalities globally in 2019. Most of these mortalities occurred in Asian countries. The Global Air Report also revealed that 84% of the worldwide population resides where PM2.5 levels exceeded recommended limits by the World Health Organization (WHO) (26). Africa is frequently disregarded in discussions about air quality. But many African cities are facing significant issues with air pollution due to the burning of solid fuels for home use, vehicles emitting exhaust fumes and emissions from industries. The United Nations Environment Programme reported that air pollution has taken its toll on Africa’s population, now responsible for over 700,000 premature deaths every year. Children, elderly individuals and people with chronic diseases suffer more significantly after being exposed to increased pollutant levels (27).

Climate change

Human activities that emit large volumes of greenhouse gases into the atmosphere are the fundamental driver of climate change. These pollutants absorb and retain solar heat, rising global temperatures, modify precipitation patterns, affect wind speeds and have severe implications for ecosystems and people around the planet. Rising sea levels, melting glaciers and fatal severe weather events are all negative consequences of climate change. As a result, climate change has the potential to affect air quality dramatically by escalating the levels of pollutants and allergens in the atmosphere. Higher temperatures can boost ground-level ozone as well as pollen production. Natural disasters such as fires have become more common and severe as a result of climate change. These disasters often result in a substantial amount of PM2.5 being discharged into the air (28).

Reasons for change in air quality

Manufacturing

The emission of numerous contaminants into the environment during manufacturing operations has a severe effect on air quality. The combustion of fossil fuels such as coal or oil, for example, can emit a range of pollutants including SO₂, NO₂, and PM2.5. Furthermore, the use of chemicals and solvents can release volatile organic compounds (VOCs) into the air, which can then react with other pollutants and form ground level ozone. The energy consumed by facilities can result in emissions of greenhouse gases, such as carbon dioxide (29). In particular, daily and chronic occupational exposures place workers at increased risk of developing respiratory diseases (30-34). By reducing emissions from these manufacturing operations, employees would be exposed to less polluted work environments and the overall air quality would improve for everyone.

Traffic density

Traffic density can affect air quality due to harmful emissions from automobiles. These pollutants include carbon monoxide, nitrogen oxides, and small particles, all of which can damage human health and the environment. The number of cars on the road and the amount of air pollution increases with greater traffic density. In metropolitan regions with high vehicle and human densities, traffic density is often heavy. Those individuals who live or work close to major roads or highways are therefore more likely to be exposed to pollution. Additionally, changes in temperature, precipitation patterns, and meteorological events brought on by the release of greenhouse gases can have a variety of detrimental effects on air quality (15).

Increase in billions of gallons used each year

The burning of fossil fuels results in an alarming quantity of pollutants being launched into the atmosphere, with contaminants such as carbon monoxide, NO₂ and PM2.5. These emissions can have negative consequences for human health and long-term environmental damage. Greater use of these fuels has led to a surge in greenhouse gas emissions that can affect air quality, temperatures, precipitation levels and atmospheric patterns. In regions with excessive automobile traffic, vehicle exhaust is a prime contributor to this airborn pollution. Industries that are heavily dependent upon fossil fuels to generate energy will amplify atmospheric pollution as demand for fuel increases. This development is further compounded by the fact that there will be a corresponding spike in emissions from these operations (35).

Natural events and weather

Natural occurrences such as wildfires, dust storms, volcanic eruptions and changes in weather patterns can also impact air quality. One illustration is stagnant air conditions, which can trap pollutants near the earth surface and increase the amounts of pollutants like ozone and PM2.5 in the atmosphere. Strong winds can spread contaminants and enhance air quality (36).

Disparities in asthma incidence and mortality

Urban vs. suburban

As researchers have identified social determinants of health to be critical in understanding disparities in asthma incidence and mortality. Of these social determinants of health, one of the most critical is housing (37). Compared to their suburban counterparts, urban housing has been found to have higher incidences of indoor asthma-triggering allergens like mold, pest and dust mite allergens (38). In a study of urban homes, a pooled analysis found that housing conditions including water leaks, the presence of cracks and holes in walls, and homes built prior to 1951 were associated with a higher risk of exposure to asthma allergens (39). Additionally, in a low-income urban setting, homeowners are limited by the cost burden of the repairs that would decrease allergen exposure and renting tenants have limited control over the maintenance of their homes (40,41). Low-quality housing influences the incidence of asthma, and racial and ethnic minorities in these homes are disproportionately affected. This structural racism over multiple decades stems from historical discriminatory housing practices (42,43).

Race and other social determinants vs. asthma incidence and outcome

Race and ethnicity are social determinants of health that have been shown to affect asthma burden (44,45). Reviews have shown that rates of uncontrolled asthma are higher in African American and Hispanic children. Also, minority children seen by minority-serving providers are less likely to receive inhaled steroids from community health clinics and hospital clinics. Additionally, a report has attributed disparities in race and ethnicity to socioeconomic status. Hughes and colleagues found that even when controlling for socioeconomic status, non-Hispanic black households were more likely to have children with an asthma diagnosis and have asthma-related emergency department visits (46). Regarding outcomes, African American and Hispanic children have more indicators of poorly controlled asthma including higher rates of emergency room visits, rescue medication usage and lower use of inhaled corticosteroids for maintenance therapy (47). A large national-level study showed that when combining both inpatient and outpatient mortality, Black and Hispanic children were at increased risk of mortality (48,49). These associations highlight the disparities in asthma care in the outpatient and pre-hospital settings.

Relationship of air quality with asthma

The World Health Organization (WHO) has set firm standards for air quality and unfortunately, nearly 99% of the planet’s population lives with air pollution that surpasses these guidelines (50). Air contamination can take on two distinct forms—gaseous or PM—which together negatively affect both outdoor and indoor air quality. Sources of this hazardous contamination include fires, cigarette smoke, and most notably fuel-burning activities such as cars on the road (51). It is therefore crucial to mitigate these pollutants in order to ensure safe living spaces now and in the future. Additionally, exposure to traffic-related air pollutants has been linked to the development of asthma in children. Yet, its effects on adult asthma remain unknown. However, it is believed that inhaling outdoor pollutants can lead to increases in both asthma symptoms and hospitalizations in a very direct fashion; longer exposure and a greater level of pollution only exacerbate the condition (52).

Lung cancer incidence and trend over the last 40 years

The American Cancer Society reports that there were 236,740 new cases of lung cancer in the United States in 2022. Of these cases, 117,910 cases occurred in males and 118,830 cases occurred in females (53). The estimated number of deaths from lung cancer in 2022 was 130,180. In the last 40 years, there has been an overall decline in both the incidence and mortality from lung cancer. The decline in lung cancer incidence has primarily been attributed to decreases in smoking rates. Changes in lung cancer incidence among non-smokers remain unclear.

Relationship of air quality with other lung-related illnesses

The quality of indoor and outside air is often harmed by various pollutants and has been associated with the development of multiple lung-related illnesses. Previous literature has established a connection between unfavorable air conditions and COPD exacerbations (54). In addition to its long-term impact, air pollution can have short-term negative health consequences. Furthermore, air pollution may be responsible for increasing the likelihood of respiratory infections, both upper and lower respiratory illnesses, by altering the lung microbiome (55). It has been widely accepted that poor air quality and elevated levels of PM2.5 can have severe adverse effects on a variety of lung diseases. Idiopathic pulmonary fibrosis and cystic fibrosis are two respiratory diseases that have been linked to poor environmental factors (56,57). However, research into the relationship between air pollution and pneumoconiosis or benign lung tumors is still inconclusive. Further research is required to gain a thorough understanding of the potential long-term health impacts associated with airborne pollutants (58).

Relationship of air quality with lung cancer

While smoking and tobacco use are the main risk factors for lung cancer, air pollutants and PM2.5 were classified as a class 1 human carcinogen by the International Agency for Research on Cancer in 2013 (59). Particularly amongst non-smokers, air pollutants are of great interest as a mechanism of lung cancer development. Several epidemiological, observational research and meta-analyses have validated this link (60-62). Particulate matter smaller than 2.5 µm have generated special concern as a carcinogen due to their very porous surface, which allows them to transmit cancer-causing substances into the respiratory system. One prospective study revealed that exposure to environmental pollution may work in concert with a genetic propensity to cause lung cancer (63). Furthermore, a recent article by Xue and colleagues emphasizes the numerous air contaminants that have been related to the occurrence of cancer as well as the pathophysiological processes that include oxidative stress, epigenetic modifications and direct DNA damage (64). There are also numerous international studies that support an association between air quality and lung cancer (65,66).

Small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC) are two of the more prevalent pulmonary neoplasms, and both are associated with a variety of ecological factors. SCLC is occasionally linked to long-term exposure to hazardous substances like asbestos fibers and radon gas. Prolonged exposure to pollutants such as PM2.5 and NO₂ have a direct correlation to NSCLC incidence, increasing relative risk by 1.54 compared to those not exposed (59). Interestingly, exposure to PM2.5 even within the first 2 months after undergoing lung cancer resection may drastically reduce the survival of patients with lung cancer (67). Collectively, these results illustrate the association of air pollution and lung cancer.

Conclusions

Air pollution is an environmental hazard that is associated with the development of lung-related illnesses. Improving air quality will reduce the incidence of these diseases. Raising awareness is a pivotal step in safeguarding both the environment and public health. Future research should continue to investigate the links and underlying causes between poor air quality and lung disease. Ultimately, improving air quality is a complicated process that demands a multifaceted approach and tailored solutions to be effective.

Supplementary

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