22. Main cause of respiratory problem arising frompollution from automobile combustion is due to-
    (1) NO_x (2) SO₂
    (3) SPM<10µm (4) SPM>50µm

Automobile combustion is a major source of urban air pollution, contributing to a range of respiratory and cardiovascular health problems. Among the pollutants emitted by vehicles—including nitrogen oxides (NOx), sulfur dioxide (SO₂), and suspended particulate matter (SPM)—fine particulate matter smaller than 10 micrometers (SPM<10µm) is the primary cause of respiratory issues. This article explores the impact of these pollutants, explains why fine particulate matter is the most significant threat to lung health, and highlights the risks and mechanisms behind respiratory diseases caused by automobile emissions.

The Pollutants from Automobile Combustion

Internal combustion engines in cars, trucks, and motorcycles emit a variety of pollutants, each with distinct effects on human health and the environment:

• Nitrogen Oxides (NOx): Includes nitric oxide (NO) and nitrogen dioxide (NO₂). NOx contributes to smog formation and can irritate the respiratory tract, but it is not the main direct cause of respiratory problems in most cases.

• Sulfur Dioxide (SO₂): Emitted mainly from diesel engines and older vehicles, SO₂ can cause airway irritation and worsen asthma, but modern fuel standards have reduced its prevalence in many regions.

• Suspended Particulate Matter (SPM): A mixture of solid particles and liquid droplets found in the air. SPM is classified by size, with fine particulate matter (PM10 and PM2.5) being the most harmful to respiratory health.

Why Fine Particulate Matter (SPM<10µm) Is the Main Cause of Respiratory Problems

Fine particulate matter—especially particles smaller than 10 micrometers (PM10)—poses the greatest risk to respiratory health. Here’s why:

1. Deep Lung Penetration

Particles smaller than 10 micrometers can bypass the natural defenses of the nose and throat and penetrate deep into the lungs, reaching the sensitive bronchial and alveolar regions. Some ultrafine particles (less than 2.5 micrometers, or PM2.5) can even enter the bloodstream, causing systemic effects.

2. Increased Inflammation and Oxidative Stress

Fine and ultrafine particles induce oxidative stress and inflammation in the respiratory tract. They stimulate innate and acquired immune responses, leading to increased airway inflammation, exacerbation of asthma, and reduced lung function. Chronic exposure can result in long-term lung damage and increased susceptibility to infections.

3. Aggravation of Existing Conditions

Exposure to PM10 and PM2.5 is associated with worsening of chronic respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD), and bronchitis. It can also lead to increased hospital admissions, emergency room visits, and even premature death, especially in vulnerable populations like children, the elderly, and those with pre-existing heart or lung conditions.

4. Reduced Lung Function

Short-term exposure to fine particulate matter can cause temporary loss of lung function in healthy individuals and reduce lung function growth in children. Long-term exposure is linked to reduced pulmonary diffusing capacity and an increased risk of lung cancer.

Comparing the Pollutants

Let’s review the options in the context of respiratory problems caused by automobile pollution:

• NOx: Contributes to smog and can irritate the airways, but is not the main direct cause of respiratory problems.

• SO₂: Can irritate the airways and worsen asthma, but is less prevalent in modern vehicle emissions due to improved fuel standards.

• SPM<10µm: The main cause of respiratory problems. Fine particulate matter penetrates deep into the lungs, causing inflammation, reduced lung function, and exacerbation of chronic diseases.

• SPM>50µm: Large particles are generally trapped in the nose and throat and do not reach the lower respiratory tract, so they pose much less risk to lung health.

Therefore, the main cause of respiratory problems arising from automobile combustion is fine particulate matter smaller than 10 micrometers (SPM<10µm).

Mechanisms of Lung Damage from Fine Particulate Matter

The mechanisms by which fine particulate matter causes respiratory problems include:

• Direct Irritation: Particles irritate the airways, leading to coughing, wheezing, and shortness of breath.

• Oxidative Stress: Fine particles generate reactive oxygen species, causing oxidative damage to lung cells and tissues.

• Inflammation: The immune system responds to particles with inflammation, which can become chronic and lead to tissue damage.

• Impaired Clearance: Chronic exposure to high concentrations of fine and ultrafine particles can overwhelm the lung’s natural clearance mechanisms, leading to particle accumulation, chronic inflammation, and even tumor development in animal models.

Health Impacts of Automobile Pollution

The health impacts of automobile pollution are significant and wide-ranging:

• Acute Effects: Short-term exposure can cause coughing, throat irritation, chest tightness, and reduced lung function.

• Chronic Effects: Long-term exposure is linked to the development and progression of chronic respiratory diseases, reduced lung function, and increased risk of lung cancer.

• Vulnerable Populations: Children, the elderly, and individuals with pre-existing heart or lung conditions are at greatest risk.

Environmental and Societal Consequences

In addition to health effects, fine particulate matter from automobile pollution contributes to:

• Reduced Visibility: PM10 and PM2.5 are the main causes of haze and reduced visibility in urban areas.

• Environmental Damage: Particulate matter can acidify lakes and streams, deplete soil nutrients, and harm sensitive ecosystems.

• Economic Costs: Increased healthcare costs, lost productivity, and premature mortality place a significant burden on society.

Mitigation Strategies

Reducing the impact of fine particulate matter from automobile combustion requires a combination of technological, regulatory, and behavioral strategies:

• Vehicle Emissions Standards: Stricter emissions standards for new vehicles and the adoption of cleaner fuels can reduce particulate emissions.

• Promotion of Public Transit: Encouraging the use of public transportation, cycling, and walking can reduce the number of vehicles on the road.

• Urban Planning: Designing cities to reduce traffic congestion and promote green spaces can help lower pollution levels.

• Public Awareness: Educating the public about the health risks of air pollution and ways to reduce exposure is essential.

Key Takeaways

• Fine particulate matter smaller than 10 micrometers (SPM<10µm) is the main cause of respiratory problems from automobile pollution.

• These particles penetrate deep into the lungs, causing inflammation, reduced lung function, and exacerbation of chronic diseases.

• NOx and SO₂ can irritate the airways but are not the primary cause of respiratory problems.

• Large particles (SPM>50µm) are trapped in the upper respiratory tract and pose little risk to lung health.

• Reducing exposure to fine particulate matter is essential for protecting respiratory health and reducing the burden of pollution-related diseases.

Summary Table

Conclusion

The main cause of respiratory problems arising from pollution from automobile combustion is fine particulate matter smaller than 10 micrometers (SPM<10µm). These tiny particles penetrate deep into the lungs, causing inflammation, reduced lung function, and exacerbation of chronic respiratory diseases. Reducing emissions of fine particulate matter from vehicles is essential for protecting public health and ensuring cleaner air in our cities.

In summary, the correct answer is:
(3) SPM<10µm.
Fine particulate matter from automobile combustion is the primary threat to respiratory health, highlighting the importance of clean air policies and sustainable transportation solutions.