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(25 pts) Imagine that you are calibrating some meteorological sensors using a sp

ID: 120822 • Letter: #

Question

(25 pts) Imagine that you are calibrating some meteorological sensors using a specially designed closed and insulating chamber, which allows for the pressure and temperature to be varied. The mass of the air within the chamber remains constant and the pressure is controlled by changing the interior volume (imagine a piston configuration). Initially, the chamber is at a pressure of 1000 hPa and a temperature of 20 C . The relative humidity of the air within the chamber is 20%. What will be the relative humidity of the air if the temperature is decreased by 10 C and the pressure is reduced by 200 hPa?

Explanation / Answer

Saturated vapor pressure (ps) at 20o c = 6.11 * 10^((7.5*20)/237.3+20)) = 23.39 hPa

Saturated vapor pressure (ps)at 10o C = 6.11 * 10^((7.5*10)/237.3+10)) = 18.53 hPa

Relative humidity at 20o C = p/ps *100

20 =( p/ 23.39) *100

Vapor pressure (p) = 4.67 hPa

then,

relative humidity at 10 o C = p/ps *100

= (4.678*100)/18.53

= 25.25 %