Humidity

 

Contents

1. Introduction

2. Related Material

3. Instrumentation

4. Local Charts

Installing the relative humidity and temperature probe. The probe is designed for long term, unattended applications. It weighs 0.6 lbs and can operature between -40°C to +60°C.

Installing TempRH at Coal Oil Point

 

1. INTRODUCTION

1.1 DEFINITION

Definition:
 Humidity is a measure of the moisture content of air. Several types of humidity measures exist, including relative humidity, specific humidity, and dew point.

 

1.2 KEY FACTS

Keys Facts:

-Humidity is highest closest to the ground.
-Air temperature is the dominant control on relative humidity, and relative humidity is typically at its highest during cold nights.
-Relative humidity is then at its lowest during mid day when it is the hottest outside.

 

2. RELATED MATERIAL

2.1 TYPICAL HUMIDITY PROFILES

•Lapse Conditions
    - Humidity is highest closest to the ground

•Inversion
    - Humidity is highest above ground

Vapor Pressure at Coal Oil Point


When are lapse conditions present?
When is it an inversion?
VP1=75 cm VP2=285 cm

 

2.2 DIURNAL PATTERNS IN RELATIVE HUMIDITY AND TEMPERATURE

• Air Temperature is the dominant control on RH
• Highest RH typically occurs at night when it is coldest
• Lowest RH occur mid day when it is hottest

 

 

2.3 SEASONAL PATTERNS IN HUMIDITY

•Vapor Pressure is highest in September
–Declines through Winter
–Begins to increase in spring
•Vapor Pressure is consistently higher on the coast
seasonal patterns of vapor pressure

 

 

3. INSTRUMENTATION

3.1 SLING PSYCHROMETER

•Principle:
    -Takes advantage of temperature depression resulting from evaporation by water
    -Includes a paired dry bulb and wet-bulb (moistened cloth) thermometer
    -Comparison between the dry and wet bulb temperatures provides humidity


•Implementation
    -The user moistens the wet bulb
    -The sling is rotated vigorously in air to promote evaporation
    -Humidity is determine from a psychometric table
 sling

 

 

3.2 HAIR HYGROMETER

•Hair Hygrometer
–First invented by Horace Benedict in 1783
•Principle:
–Takes advantage of the fact that the length of a synthetic or human hair varies with humidity
Hair hygrometer for measuring relative humidity

 

 

3.3 TEMPERATURE AND RELATIVE HUMIDITY PROBE AT COPR

Temperature and RH Probe

 

 

 


The Temperature and Relative Humidity Probe is designed for long term, unattended applications. It weights 0.6 lbs and can operate between -40°C to +60°C

Installing TempRH at Coal Oil Pointrelative humidity and temperature probe close-up at coal oil point reserve

Installing Temperature & Relative Humidity Sensor at Coal Oil Point;
Photo by Meri Marsh; May 25, 2007

 

 

 

4. LOCAL CHARTS

4.1 RELATIVE HUMIDITY & VAPOR PRESSURE AT COPR

•Vapor Pressure varies substantially
•Vapor Pressure is highest when Relative humidity is lowest
•Relative Humidity differences are more pronounced at night than Vapor Pressure

 

4.2 RELATIVE HUMIDITY & VAPOR PRESSURE AT AIR STRIP

•Relative Humidity varies more than at COP
•Vapor Pressure does not vary substantially throughout the day
•Vapor Pressure increases late in the week

 

Humidity animation
Click here to see animations showing spatial and temporal patterns in humidity.

 


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