Vehicle exhaust emissions are comprised of carbon dioxide, water vapor, nitrogen oxides, carbon monoxide, sulfur dioxide, particulate matter (PM), and various hydrocarbons, including polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds.
Collectively, these exhaust emissions which result from internal combustion engines have become increasingly regarded as a potential health risk, with increasingly stringent standards being imposed unlimited in many parts of the world.
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Particulate matter and health
Studies have shown a relationship between PM and adverse health effects focusing on both short-term or long-term PM exposure. PM results from chemical reactions between different pollutants, and the penetration of the particles is dependent on their size.
According to the United States Environmental Protection Agency, PM includes particles >10um in diameter, called PM10, and extremely fine particles with diameters that are generally 2.5μm and smaller.
PM10 can invade the lungs after inhalation and reach the bloodstream; finer particles, PM2.5 pose a greater health risk as they can penetrate further into terminal bronchial areas as well as terminal bronchioles and alveoli. Several epidemiological studies have shown that short and long-term exposure to PM2.5 results in nasal pharyngitis, with longer-term exposure in particular related to cardiovascular diseases and infant mortality.
In addition to these effects, respiratory diseases and ill effects on the immune system are also regarded as long-term chronic outcomes. People who suffer from pneumonia, diabetes, asthma, respiratory and cardiovascular diseases are at greater risk from the PM.
Carbon monoxide is caused by the incomplete combustion of fuel. Elevated levels of carbon dioxide can cause poisoning; symptoms include dizziness, weakness, headache, vomiting, and loss of consciousness. Carbon monoxide elicits its effect through the binding of hemoglobin.
Carbon monoxide has a greater affinity to this protein, binding more tightly to cause the loss of oxygen. The outcome of this is hypoxia, ischemia, and cardiovascular disease.
Nitrogen oxides are a potent irritant of the respiratory system, penetrating deep into lung tissue, causing respiratory diseases, wheezing, bronchospasm, and even pulmonary edema at high levels. Moreover, concentrations over 2 ppm can affect the immune system, particularly the CD8+ T cells.
Long-term exposure to nitrogen dioxide is reported to be linked to the development of chronic lung disease, as well as impairing individuals' sense of smell.
Sulfur dioxide affects humans, animals, and plants. The most acceptable cohorts include those with lung disease, the elderly, and children. The major health outcomes associated with inhalation of sulfur dioxide include mucus production, bronchitis, and bronchospasm.
Sulfur dioxide is also regarded as a sensory irritant, capable of deep penetration into the lung where it is converted into bisulfite and can interact with the sensory receptors to cause bronchoconstriction. Other health effects include damage to the eyes (lacrimation and corneal opacity) and mucous membranes, as well as exacerbation of pre-existing cardiovascular diseases.
Lead is a heavy metal that can be emitted from some petrol motor engines. Lead can enter the body through inhalation, ingestion, and absorption through the skin. When lead is inhaled, it accumulates in the blood and soft tissue as well as the lungs and liver, cardiovascular, nervous, and reproductive systems, and bones. Other effects include loss of concentration and memory as well as increased joint and muscle pain
Newborns and young children are highly susceptible to low doses of lead; it is a neurotoxicant and can affect the development of young children resulting in learning disabilities, hyperactivity, impaired memory, and even mental retardation.
Short term versus long term effects of pollution
The short-term effects of pollution are temporary and range from simple discomfort such as irritated eyes, skin, nose, and throat as well as acute symptoms such as coughing, wheezing, breathing difficulties, and chest tightness. More severe short-term effects include asthma, pneumonia, bronchitis, and lung and heart problems.
Extended long-term exposure to these pollutants can aggravate these symptoms causing more widespread reproductive, neurological, and respiratory effects; these can culminate in a variety of different types of cancer, and in rare cases, death. Death is increasingly likely following the long-term effects of chronic exposure. Long-term effects are more likely in individuals with a predisposing disease state.
Although the short and long-term effects of vehicle exhaust emissions on health are unequivocally potent, the nature of the damage to cells is dependent on the pollutant component involved, its source, and concentration. Health effects are also related to the country, season, region, and time.
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