Table 2. Summary of the environmental and meteorological variables in urban areas in Beijing during the study period.
| Variables | Percentiles | ||||||
|---|---|---|---|---|---|---|---|
| Mean | SD | Min | 25th | Median | 75th | Max | |
| PM2.5 (μg/m3) | 102.1 | 73.6 | 6.7 | 53.1 | 82.4 | 129.5 | 508.5 |
| SO2 (μg/m3) | 31.2 | 25.7 | 3.6 | 11.0 | 23.3 | 43.7 | 133.8 |
| O3 (μg/m3) | 104.3 | 68.3 | 4.4 | 53.0 | 89.4 | 146.5 | 305.4 |
| CO (mg/m3) | 2.2 | 1.5 | 0.3 | 1.2 | 1.9 | 2.6 | 17.7 |
| NO2 (μg/m3) | 66.7 | 25.0 | 12.4 | 50.1 | 62.3 | 78.3 | 171.5 |
| Temperature (°C) | 11.3 | 11.6 | -12.6 | 1.2 | 11.0 | 22.2 | 29.0 |
| Relative humidity (%) | 58.7 | 17.3 | 18.9 | 46.7 | 59.0 | 73.3 | 93.3 |
Abbreviations: PM2.5-particles with an aerodynamic diameter ≤ 2.5 μm, SO2-sulfur dioxide, O3-ozone, CO-carbon monoxide, NO2-nitrogen dioxide, SD-standard deviation, Max-maximum, and Min-minimum.