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Water Vapor Sorption by the Walls and Sensors of Stomatal Diffusion Porometers 1
Author(s) -
Gandar P. W.,
Tanner C. B.
Publication year - 1976
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1976.00021962006800020009x
Subject(s) - sorption , water vapor , relative humidity , humidity , diffusion , materials science , wax , acrylic acid , analytical chemistry (journal) , chemistry , adsorption , composite material , environmental chemistry , polymer , thermodynamics , organic chemistry , monomer , physics
The operation of stomatal diffusion porometers is affected by sorption of water vapor by the humidity sensor and the walls of the porometer. The objective of this study was to assess the amount of water vapor sorbed by Dunmore lithium chloride humidity sensors and by materials commonly used in porometer construction. Measurements of water sorption by stainless steel, acrylic plastic, wax‐coated acrylic, and humidity sensors were made at different relative humidities (RH) in the range of 22 to 28% RH and temperatures of 20, 25, and 30 C, by measuring the vapor mass balance at different RH. Stainless steel absorbed 0.5 ± 0.25 μ g cm −2 of water vapor at 22 to 28% RH and temperatures from 20 to 30 C. Water vapor diffused into acrylic (D ≈ 2.5 × 10 −9 cm 2 sec −1 ) so the sorption was not constant. Coating acrylic with wax significantly reduced water sorption; at 25 C the sorption of waxed acrylic was in the range 0.9 to 1.2 μ g cm −2 . The sorption by the humidity sensors varied with RH, temperature, sensor age, and prior treatment. At 25 C and 26% RH the sorption of the external sensor surface was about 40 μ g cm −2 . Materials with low sorptivities, such as stainless steel or waxed surfaces, should be used in the construction of diffusion porometers. Procedures which minimize variability in sorption, such as storage at RH near the operating range of the sensor, should be followed when porometers are used.