Which units are often used to express pollutant concentration in the atmosphere?

The correct units for expressing pollutant concentration in the atmosphere typically include micrograms per cubic meter (µg/m³), as this measurement is specifically designed to quantify the mass of pollutant per volume of air, which is relevant when assessing air quality and exposure levels. Atmospheric concentrations of pollutants, particularly at low levels, are often measured in this manner to facilitate comparisons against established health and safety standards.

When considering the other options, parts per million (ppm) can also represent pollutant concentration, especially for gases; however, it is often less precise than µg/m³ for fine particulate measurements. Milligrams per liter (mg/L) is a common unit for liquids, and grams per cubic centimeter (g/cm³) typically applies to solid densities or liquids but is not appropriate for airborne pollutants. Thus, µg/m³ is the preferred unit for accurately assessing and expressing concentrations of pollutants in the atmosphere.