Please some help me when a past exam question! (air pollution air sampler calculation)

Question

At the end of the opening ceremony for the 2012 London Olympics there was a huge fireworks display. A heavy-duty total suspended particulate (TSP) sampler was set up to run for 24 hours on the roof of the stadium at an average of 32.45 litres per hour. At the end of the ceremony, the filter has a weight of 67.2837g. The initial weight was 49.1588g. Calculate the average TSP concentration in the atmosphere immediately above the stadium in **mg m-3 hr-1**

 

I have (incorrectly) said:

TSP (mg/m3/hr) = [(Wf-Wi) x 1000 (to get mg from g)/V (m3)]/24 (hrs)
where:

TSP = average mass concentration of total suspended particulate matter per hour, mg/m3/hr;
Wi = initial weight of clean filter, g;
Wf = final weight of exposed filter, g;
V = air volume sampled, m3 (L --> m3) 778.8 Liters/1000 = 0.7788 m3
1000 = conversion of g to mg.
24 (hrs) to get per hour.

Therefore: TSP(mg/m3/hr)= 18127.9/ 0.778799999999999937 cubic meters/24 hours
=969mg/m3/hr.

Where have i gone wrong? Please help.

Answer 1

Anna,

 

I see 2 errors, one trivial, the other major.

 

The trivial one is that the TSP filter weight difference is 18.12(4)9 g, not your 18.12(7)9 g.

 

The more serious error is that the problem asks for the "average" concentration, not the final concentration as you computed.

 

Hence average ΔW = 18.1249/2 = 9.06245 g/m³/24 hr.

 

Correcting both problems, I get 484.9 mg/m³/hr as the average TSP per hour per cubic meter.