Particulate Matter (PM) is a primary component of air pollution, consisting of a complex mix of gases and microscopic solid or liquid droplets. PM exposure has been directly linked to various adverse health outcomes, making it a serious environmental risk to human health. Understanding PM levels is a foundational step in mitigating personal risk, especially for those living in areas with poor air quality. This article explains the nature of this pollutant, its health implications, how its concentration is measured, and steps individuals can take for protection.
What is Particulate Matter
Particulate matter is a mixture of solid particles and liquid droplets suspended in the air. Their size determines how deeply they can penetrate the respiratory system. Scientists categorize PM based on its diameter, with two sizes of concern: PM10 and PM2.5.
PM10 refers to inhalable coarse particles with diameters of 10 micrometers or less. These larger particles generally include dust from construction sites, pollen, mold spores, and fragments from unpaved roads. Because of their size, PM10 particles tend to deposit in the upper part of the respiratory tract, such as the nose and throat.
PM2.5 includes fine inhalable particles with diameters of 2.5 micrometers and smaller. These particles are often combustion byproducts, originating from sources like vehicle exhaust, power plant emissions, and wildfire smoke. Their diminutive size allows them to travel much deeper into the lungs and even enter the bloodstream, posing the greatest threat to health. Particle pollution worldwide is generated by everyday activities, making it a persistent global issue.
Health Consequences of Exposure
When inhaled, fine particulate matter bypasses the body’s natural defenses and settles deep within the lungs. Short-term exposure commonly results in acute symptoms such as coughing, throat irritation, and shortness of breath. For individuals with pre-existing conditions like asthma or Chronic Obstructive Pulmonary Disease (COPD), even brief exposure can precipitate severe asthma attacks or worsen respiratory symptoms.
Long-term exposure to PM2.5 affects the cardiovascular system. Once in the bloodstream, the particles and the inflammatory response they trigger can lead to vascular damage and reduced blood vessel elasticity. This chronic inflammation destabilizes arterial plaque, increasing the risk of heart attacks, irregular heartbeats, and strokes. Children, older adults, and people with underlying heart or lung diseases are the most susceptible groups.
Chronic exposure also contributes to the development and acceleration of chronic respiratory diseases, including chronic bronchitis and lung cancer. Evidence suggests that long-term exposure can slow lung function growth in children, resulting in smaller lungs later in life. The medical consensus is that fine particulate matter is the air pollutant associated with the greatest proportion of adverse health effects globally.
How PM Levels are Measured and Reported
Particulate matter concentrations are quantified using a mass per volume measurement: micrograms per cubic meter ($\mu g/m^3$). This metric represents the total weight of PM suspended within a defined volume of air. Air quality monitors draw a measured volume of air through a filter, which is then weighed to determine the particle concentration.
This data is translated into the Air Quality Index (AQI), a color-coded scale designed to communicate the current level of air pollution and associated health concerns. The scale ranges from 0 to 500 and is divided into categories such as “Good” (0-50, green), “Moderate” (51-100, yellow), and “Unhealthy” (151-200, red).
The AQI is calculated based on the highest concentration of several major pollutants, including PM2.5 and PM10, using established breakpoints set by the U.S. National Ambient Air Quality Standards (NAAQS). An AQI reading above 100 signifies air quality that is unhealthy for sensitive groups, while readings above 200 are deemed very unhealthy for everyone. Public notification systems rely on this index to provide real-time information.
Protecting Yourself When Air Quality is Poor
When the AQI enters the “Unhealthy for Sensitive Groups” or higher categories, the most direct action is to limit time spent outdoors. It is especially important to avoid strenuous activities like running or cycling, as strenuous exercise increases the amount of air inhaled, driving pollutants deeper into the lungs.
Indoors, keeping windows and doors closed prevents outside air infiltration. A High-Efficiency Particulate Air (HEPA) filter-equipped air purifier can significantly reduce indoor PM levels by capturing fine particles.
When outdoor activity is unavoidable during periods of poor air quality, wearing a certified N95 or N99 respirator mask provides a physical barrier against fine particles. These respirators are designed to filter out at least 95% of airborne particles. Simple community actions, such as minimizing activities that generate smoke or dust, also contribute to overall air quality improvement.