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: μ1 ≠ μ2, 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).
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 . | ||||
|---|---|---|---|---|---|---|
| Component . | t-value . | Sig. . | Pw,i vs. Pb,i . | t-value . | Sig. . | Ri vs. 1 . |
| TOC | 3.204 | 0.003 | Pw≫Pb | –0.010 | 0.992 | ≈1 |
| NO3– | 6.945 | 0 | Pw≫Pb | –0.222 | 0.826 | ≈1 |
| Cl– | 3.153 | 0.004 | Pw≫Pb | –0.502 | 0.621 | ≈1 |
| oxalic acid | –1.732 | 0.094 | Pw ≈ Pb | 1.028 | 0.327 | ≈1 |
| NH4+ | 8.237 | 0 | Pw≫Pb | 3.160 | 0.005 | >1 |
| acetic acid | 4.405 | 0 | Pw≫Pb | 3.453 | 0.004 | >1 |
| formic acid | 3.261 | 0.005 | Pw≫Pb | 2.569 | 0.022 | >1 |
| Ca2+ | –16.128 | 0 | Pw≪Pb | –59.643 | 0 | <1 |
| F– | –3.901 | 0 | Pw≪Pb | –7.574 | 0 | <1 |
| K+ | –0.064 | 0.949 | Pw ≈ Pb | –19.791 | 0 | <1 |
| Mg2+ | 1.832 | 0.076 | Pw ≈ Pb | –5.347 | 0 | <1 |
| SO42– | –0.98 | 0.333 | Pw ≈ Pb | –5.481 | 0 | <1 |
| Na+ | 2.426 | 0.023 | Pw≫Pb | –15.396 | 0 | <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 . | ||||
|---|---|---|---|---|---|---|
| Component . | t-value . | Sig. . | Pw,i vs. Pb,i . | t-value . | Sig. . | Ri vs. 1 . |
| TOC | 3.204 | 0.003 | Pw≫Pb | –0.010 | 0.992 | ≈1 |
| NO3– | 6.945 | 0 | Pw≫Pb | –0.222 | 0.826 | ≈1 |
| Cl– | 3.153 | 0.004 | Pw≫Pb | –0.502 | 0.621 | ≈1 |
| oxalic acid | –1.732 | 0.094 | Pw ≈ Pb | 1.028 | 0.327 | ≈1 |
| NH4+ | 8.237 | 0 | Pw≫Pb | 3.160 | 0.005 | >1 |
| acetic acid | 4.405 | 0 | Pw≫Pb | 3.453 | 0.004 | >1 |
| formic acid | 3.261 | 0.005 | Pw≫Pb | 2.569 | 0.022 | >1 |
| Ca2+ | –16.128 | 0 | Pw≪Pb | –59.643 | 0 | <1 |
| F– | –3.901 | 0 | Pw≪Pb | –7.574 | 0 | <1 |
| K+ | –0.064 | 0.949 | Pw ≈ Pb | –19.791 | 0 | <1 |
| Mg2+ | 1.832 | 0.076 | Pw ≈ Pb | –5.347 | 0 | <1 |
| SO42– | –0.98 | 0.333 | Pw ≈ Pb | –5.481 | 0 | <1 |
| Na+ | 2.426 | 0.023 | Pw≫Pb | –15.396 | 0 | <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.