Table 1.
Calculated spatial extent from illustrative case study under differing assumptions and definitions
| Factor under study | Emission rate (μg/m·s) | Background concentration (μg/m3) | Meteorological conditions | Definition of spatial extent | Estimated spatial extent (m) | ||
| Wind speed (m/s) | Stability class | Comparison method | Threshold | ||||
| Spatial extent definition | 5 | 0 | 4 | D | Absolute | 0.25 μg/m3 | 70 |
| 5 | 0 | 4 | D | Absolute | 0.1 μg/m3 | 190 | |
| 5 | 0 | 4 | D | Absolute | 0.05 μg/m3 | 430 | |
| 5 | 0 | 4 | D | Relative | 50% of reference | 60 | |
| 5 | 0 | 4 | D | Relative | 20% of reference | 170 | |
| 5 | 0 | 4 | D | Relative | 10% of reference | 380 | |
| Emission rate | 2.5 | 0 | 4 | D | Absolute | 0.1 μg/m3 | 90 |
| 10 | 0 | 4 | D | Absolute | 0.1 μg/m3 | 430 | |
| Background concentration | 5 | 0.25 | 4 | D | Relative | 50% of reference | 120 |
| 5 | 1 | 4 | D | Relative | 50% of reference | N/A | |
| Meteorological factor | 5 | 0 | 3 | F | Absolute | 0.25 μg/m3 | 350 |
| 5 | 0 | 2 | B | Absolute | 0.25 μg/m3 | 70 | |
| 5 | 0 | 6 | D | Absolute | 0.25 μg/m3 | 40 | |
| Health risk threshold | 5 | 0 | 4 | D | Absolute | 20 per million cancer risk | 300 |
| 5 | 0 | 4 | D | Absolute | 1 per million cancer risk | > 500 (beyond domain) | |