The pollutants which are already present in nature, but are also released in substantial amounts by man are known as quantitative pollutants.
Quantitative pollutants are those substances which are naturally present in the environment, but are termed as pollutants when their concentration (quantity) increases in the environment due to anthropogenic activities. For example, CO2 is present in the environment in quantities greater than normal, due to automobiles and industries. It is thus, classified as a quantitative pollutant.