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The two-group independent sample t-test was used to detect whether or not the population mean of the proportion of a component in the wet deposition (μ1) and that in the dust buildup (μ2) are different. The hypothesis was set: H0: μ1 = μ2; H1: μ1μ2, where H0 and H1 are null hypothesis and alternative hypothesis, respectively. According to the results of the independent sample t-test, the components can be classified into three groups (Table 5).

Table 5

Comparison of components between wet deposition, dust buildup and roof runoff

Two-group independent sample t-test for comparison between Pw,i and Pb,i
One sample t-test for comparison between Ri and 1
Componentt-valueSig.Pw,i vs. Pb,it-valueSig.Ri vs. 1
TOC 3.204 0.003 PwPb –0.010 0.992 ≈1 
NO3 6.945 PwPb –0.222 0.826 ≈1 
Cl 3.153 0.004 PwPb –0.502 0.621 ≈1 
oxalic acid –1.732 0.094 PwPb 1.028 0.327 ≈1 
NH4+ 8.237 PwPb 3.160 0.005 >1 
acetic acid 4.405 PwPb 3.453 0.004 >1 
formic acid 3.261 0.005 PwPb 2.569 0.022 >1 
Ca2+ –16.128 PwPb –59.643 <1 
F –3.901 PwPb –7.574 <1 
K+ –0.064 0.949 PwPb –19.791 <1 
Mg2+ 1.832 0.076 PwPb –5.347 <1 
SO42– –0.98 0.333 PwPb –5.481 <1 
Na+ 2.426 0.023 PwPb –15.396 <1 
Two-group independent sample t-test for comparison between Pw,i and Pb,i
One sample t-test for comparison between Ri and 1
Componentt-valueSig.Pw,i vs. Pb,it-valueSig.Ri vs. 1
TOC 3.204 0.003 PwPb –0.010 0.992 ≈1 
NO3 6.945 PwPb –0.222 0.826 ≈1 
Cl 3.153 0.004 PwPb –0.502 0.621 ≈1 
oxalic acid –1.732 0.094 PwPb 1.028 0.327 ≈1 
NH4+ 8.237 PwPb 3.160 0.005 >1 
acetic acid 4.405 PwPb 3.453 0.004 >1 
formic acid 3.261 0.005 PwPb 2.569 0.022 >1 
Ca2+ –16.128 PwPb –59.643 <1 
F –3.901 PwPb –7.574 <1 
K+ –0.064 0.949 PwPb –19.791 <1 
Mg2+ 1.832 0.076 PwPb –5.347 <1 
SO42– –0.98 0.333 PwPb –5.481 <1 
Na+ 2.426 0.023 PwPb –15.396 <1 

Pw,i the proportion of the ith component in the wet deposition; Pb,i the proportion of the ith component in the dust buildup on the rooftop; Ri the ratio of mass of the ith component in the wet deposition to that in the roof runoff.

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