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The US Occupational Safety and Health Administration recommends indoor air be maintained at 20–24.5 °C (68–76 °F) with a 20–60% relative humidity, [13] equivalent to a dew point of approximately 4.0 to 16.5 °C (39 to 62 °F) (by Simple Rule calculation below).
Various governmental agencies involved with environmental protection and with occupational safety and health have promulgated regulations limiting the allowable concentrations of gaseous pollutants in the ambient air or in emissions to the ambient air. Such regulations involve a number of different expressions of concentration.
The water in food has a tendency to evaporate, but the water vapor in the surrounding air has a tendency to condense into the food. When the two tendencies are in balance— and the air and food are stable—the air's relative humidity (expressed as a fraction instead of as a percentage) is taken to be the water activity, a w. Thus, water ...
Once air becomes saturated, water will condense to form clouds, dew or films of water over leaves. It is this last instance that makes VPD important for greenhouse regulation. If a film of water forms on a plant leaf, it becomes far more susceptible to rot. On the other hand, as the VPD increases, the plant needs to draw more water from its roots.
Its units are in parts per million (ppm) for gases and in milligrams per cubic meter (mg/m 3) for particulates such as dust, smoke and mist. The basic formula for converting between ppm and mg/m 3 for gases is ppm = (mg/m^3) * 24.45 / molecular weight. This formula is not applicable to airborne particles.
Regulations that define and limit the concentration of pollutants in the ambient air or in gaseous emissions to the ambient air are issued by various national and state (or provincial) environmental protection and occupational health and safety agencies. Such regulations involve a number of different expressions of concentration.
Dew point temperature (DPT) is the temperature at which a moist air sample at the same pressure would reach water vapor "saturation." At this point further removal of heat would result in water vapor condensing into liquid water fog or, if below freezing point, solid hoarfrost. The dew point temperature is measured easily and provides useful ...
The "dew point temperature" is an absolute measure of the moisture in air. Some facilities are being designed with dew points in the lower 50s °F, and some in the upper and lower 40s °F. [citation needed] Some facilities are being designed using desiccant wheels with gas-fired heaters to dry out the wheel enough to get the required dew points.