Office of Planning, Environment, & Realty (HEP)

# Measurement of Highway-Related Noise

## Appendix A Relative Humidity Computation

This appendix presents the procedures for converting measured dry and wet bulb temperatures into relative humidity expressed in percent.

1. Convert Dry Bulb temperature from °F to °C:

Dry, °C =[(Dry,°F) -32] /1.8

2. Convert Dry Bulb temperature from °C to °K:

Dry, °K = (Dry, °C) + 273.15

3. Repeat steps 1 and 2 to convert Wet Bulb temperature (Wet) to °K.

4. Compute the Saturation Pressure, assuming standard-day ambient atmosphere pressure, for the Dry Bulb temperature (DrySatPres):

DrySatPres = e19.163 - (4063.2 + 184089.0/Dry)/Dry

5. Repeat step 4 to compute the Saturation Pressure for the Wet Bulb temperature (WetSatPres).

6. Compute the Relative Humidity (RH) in percent:

RH, % = 100 × [WetSatPres/DrySatPres]

Updated: 7/6/2011
HEP Home Planning Environment Real Estate
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000