In Los Angeles, on days when air pollution levels are high, smog alerts are issu
ID: 802069 • Letter: I
Question
In Los Angeles, on days when air pollution levels are high, smog alerts are issued. Officials recommend that people avoid strenuous activity and remain indoors with the windows and doors closed. Determine how much protection is afforded against ozone, a key pollutant, by remaining indoors. Consider the case of a typical residence, which can be modeled as a CSTR. Assume that the volume is 250 m3 and that, even with the doors and windows closed, air leaks into the house from outdoors through cracks at a rate of 2.5 m3/min (Note: if air comes in, it should also go out, so Qin = Qout). Ozone reacts with indoor surfaces and this reaction can be represented as a first-order reaction that consumes ozone with a rate constant of 2.6 hr-1.
a. (15) Calculate the indoor/outdoor ratio of ozone under steady-state conditions.
b. (5) Comment on the effectiveness of remaining indoors as a mean of protecting oneself against outdoor ozone exposure.
Explanation / Answer
a. The indoor and outdoor ratio of ozone can be calculated under the steady state conditions by the equations
I/Q=a/a+K
where a= exchange rate of air
K= first order rate constant
I/Q= ratio of indoor to outdoor air
First we need to calculate the air exchange rate
Given Volume of room=250m3
Rate of air entering into the room=2.5m3/min
Air exchange rate/hr= 60*rate of air entering /Volume of room
=60*250/2.5
=0.6/hr
Now I/Q=a/a+K
where a=0.6/h
K=2.6/hr
=0.6/0.6+2.6
=0.6/3.2
=0.1875
b. The ozone in the air can be harmful to us especially on hot summer days. During this time there is high level of ozone in the air which is not good for our health. The risk of ozone is higher for children, people with asthma and active people like outdoor workers and people who does outdoor activities, older people and people with reduced intake of certain vitamins like C and D. The harmful effects of ozone are difficulty in breathing, deteriorate the chronic diseases like asthma and chronic bronchitis, damage the lungs and airways, coughing and soar throat. So the best way to prevent the outdoor ozone exposure is to remain indoors and keeping your doors and windows closed. If possible reduce the time of outdoor activities. Also scheduling your time for outdoor activities in the morning or evening when the level of ozone is lower and doing less strenuous exercises.
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