Porometers

Porometers are instruments used to measure porosity and pore characteristics of porous materials, or to quantify gas exchange through plant leaves. In plant physiology, the term often refers to leaf porometers, devices that estimate stomatal conductance by measuring the rate at which water vapor diffuses from the leaf interior to the surrounding air. A leaf porometer typically encloses a small leaf area in a chamber with a controlled humidity or gas environment and records the humidity differential or flux. From these measurements, stomatal conductance and sometimes transpiration rates can be inferred. Measurements are influenced by leaf temperature, ambient humidity, light, and leaf surface properties, and require careful calibration.

For non-biological samples, porometers characterize pore structure or permeability by monitoring gas flow or fluid invasion through a sample under a known pressure or concentration gradient. These instruments are used for films, membranes, ceramics, fabrics, soils, and other porous media to determine pore size distribution, total porosity, and permeability. Techniques include diffusion-based porometry and pressure-driven porometry, and results support assessments of filtration performance, drying behavior, and hydraulic properties.

Advantages include relatively rapid, non-destructive measurements (for leaves) and the ability to compare samples under standardized conditions. Limitations include sensitivity to environmental parameters, sample heterogeneity, and the need for careful calibration and method selection across different device types.

See also: stomatal conductance, pore size distribution, gas porometry.