What the key differences are between the two primary methods for quantifying and expressing PM2.5 levels in the air.
The Clarity Node-S uses an optical particle counter (OPC) that provides number and mass concentrations for PM (PM1, PM2.5, and PM10). The OPC directly measures the number of particles in the sample and converts to a mass concentration by approximating the size of the particles.
PM2.5 Mass Concentration: PM2.5 mass concentration refers to the amount of particulate matter with an aerodynamic diameter of 2.5 micrometers or smaller, expressed as a mass concentration per unit volume of air. It represents the total weight of particles present in a given volume of air. Mass concentration is typically measured in micrograms per cubic meter (µg/m³) or milligrams per cubic meter (mg/m³). This measurement provides information on the overall mass of particles, regardless of their individual size or number.
PM2.5 Number Concentration: PM2.5 number concentration, on the other hand, focuses on counting the actual number of particles with an aerodynamic diameter of 2.5 micrometers or smaller within a given volume of air. It represents the concentration of individual particles and is expressed as a number of particles per unit volume of air. Number concentration is typically measured in particles per cubic centimeter (particles/cm³) or particles per cubic meter (particles/m³). This measurement provides information on the count of particles present, regardless of their individual mass.
Why convert from the number concentration to mass concentration?
While there is growing evidence that PM number concentration is important to health impacts, PM mass concentration is most frequently the parameter of interest:
- Many countries and international organizations have established air quality standards and guidelines based on PM2.5 mass concentration.
- PM2.5 mass concentration is a key component in calculating the Air Quality Index (AQI), which is a standardized metric used to communicate air quality information to the public.