Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Pollutant | Units | Emission Standard | Coal-fired | Petroleum Coke-fired |
| --- | --- | --- | --- | --- |
| SO2 | lb/MMBTU | ≤ 0.15 | 0.0−0.04 | 0.03−0.13 |
| NOx | lb/MMBTU | ≤ 0.09 | 0.04−0.06 | 0.02 |
| Solid particulate | lb/MMBTU | ≤ 0.011 | 0.004 | 0.007 |
| PM10 | lb/MMBTU | ≤ 0.011 | 0.006 | 0.004 |
| SO3 | lb/hour | ≤ 1.1 | 0.43 | 0.0 |
| Fluoride | lb/MMBTU | ≤ 1.57×10−4 | 1.06×10−4 | 0.95×10−4 |
| Lead | lb/MMBTU | ≤ 2.6×10−5 | 0.56×10−5 | 0.59×10−5 |
| Mercury | lb/MMBTU | ≤ 1.05×10−5 | 0.095×10−5 | 0.028×10−5 |
Question:
what category does each pollutant except so3 have in common?
Answer:
Units