Yes. Filters will perform very differently in a gas/air stream than in a liquid stream. These differences can be observed by comparing flow rates and retention ratings between gas /air and liquid for the same medium. In liquid, particles generally follow the flow of the solution as it travels through the filter, and it is primarily particles that are directly intercepted by the filter matrix which will be retained. In gas/air filtration, direct interception also applies, but there are other additional mechanisms that can cause particles to be captured by the filter. These mechanisms include inertial impaction, gravitational settling, electrostatic interaction, and Brownian Motion.
Are glass microfiber filters unidirectional? Does it matter which side is up and which side faces downstream?
Glass microfiber filters are not asymmetrical, and they do not have a specific directionality (with the exception of graded density filters such as Multigrade GMF 150). The difference in texture between the sides of the filters is attributed to the web on which the filter is formed. This difference does not typically affect the filtration properties.