Particulate matter air pollution: effects on the respiratory system

Abstract

Air pollution comprises a complex mixture of gaseous and particulate components. Particulate matter (PM) air pollution is associated with 4.7 million premature deaths per year. Among modifiable risk factors, air pollution exposure contributes to 8% of disability adjusted life years and ranks above factors such as high blood pressure, smoking, and high fasting plasma glucose. As the site of entry, exposure to PM air pollution causes respiratory symptoms and is a significant cause of respiratory morbidity and mortality. In this Review, we discuss the studies that link air pollution exposure with respiratory diseases. We review the epidemiological evidence linking PM exposure and lung diseases including asthma, chronic obstructive pulmonary disease, pulmonary fibrosis, pneumonia, acute respiratory distress syndrome, and lung cancer. We also provide an overview of current knowledge about the mechanisms by which PM exerts its biological effects leading to adverse health effects in the respiratory system.

Figure 1. Particulate matter size and components.

(A) Images of urban particulate matter (PM) generated by scanning electron microscopy. Original magnification, ×2,000 (left), ×10,000 (center), and ×50,000 (right). (B) Relative sizes of PM₁₀ (coarse), PM_2.5 (fine), and PM_0.1 (ultrafine or nanoparticles) in comparison to alveolar macrophage and influenza A virus (IAV). (C) Common components of PM. Other category includes metals (Al, K, Ca), transition metals (Fe, Zn, Cd, Ti, Ag, Cu, Mn, Au, Mg, Hg, Cr, Zr, Ni, V, and Co), nonmetals, halogens, and lanthanides (7, 272).

Figure 2. Mechanisms by which PM air pollution affects the respiratory system.

Inhaled PM induces an inflammatory response in the lung. PM acts on the cells of the lung, including airway and alveolar epithelial cells and macrophages, causing mitochondrial ROS-dependent transcriptional responses, including NF-κB and NRF2 activation. Oxidative stress promotes production of proinflammatory cytokines and oxidative damage. These PM-induced changes cause lung and systemic inflammation (due to spillover of cytokines into the circulation), altered immune response, and epigenetic changes. Clinically, PM-induced effects are exhibited through the development of respiratory symptoms such as cough and dyspnea in healthy individuals. PM exposure is associated with the development, progression, and exacerbation of lung diseases, including asthma, COPD, pulmonary fibrosis, pneumonia, ARDS, and lung cancer.