As a result of multiple efforts the PM₁₀ mass concentration has been reduced in many developed countries in the past 2 decades. However, as the PM₁₀ mass concentrations are decreasing, the potential relative bias caused by water interactions is likely becoming more significant. This is simply due to the fact that the bias caused by adsorption or desorption of water on and from the filter medium becomes proportionally more significant relative to the aerosol mass deposited on the filter.