Question

Many houses in the Washington area experience indoor air pollution by radon. A house of a volume V = 300 m³ has air leaking in from the soil with a radon concentration of 5000 pCi/L and rate of 20 L/h. During the winter time, the average rate of fresh radon-free air entering the house is only 400 L/h. Radon undergoes decay following a first order reaction with a rate constant k = 0.18/day. The house can be approximated as a CSTR.  

a)      (2 %) Make a schematic drawing of the house showing air flows, concentrations, volume and rate.

b)     (2 %) What is the air flow rate leaving the house?

c)      (2 %) Write the general mass balance equation for radon in the house

d)     (5 %) Calculate the steady state radon concentration in the house

e)    (5 %) How much fresh air would have to come into the house per hour to reduce the radon concentration to the EPA guideline value of 4 pCi/L? If you did not get a result for d) you can assume that the radon concentration in the house is 50 pCi/L

f)   (2 %) How does the residence time of radon in the house compare to the half life of radon: does decay make a significant contribution to radon removal?

g)      (2 %) What else (in addition to ventilation) can be done to reduce radon levels in the house on a long term basis?

Answer 1

As per the answering guidelines, I have provided the solution to the first 4 parts of the question.

Cheers.