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Note 11 - Business Segment and Geographic Financial Data (Tables) | 6 Months Ended
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Jun. 30, 2026
Notes Tables |
Segment Reporting [Table Text Block] |
|  | Air Pollution |  |  | FUEL CHEM |  |  |  |  |  |  |  |  |
Three months ended June 30, 2026 |  | Control Segment |  |  | Segment |  |  | Other |  |  | Total |
Revenues from external customers |  | $ | 2,785 |  |  | $ | 3,700 |  |  | $ | — |  |  | $ | 6,485 |
Cost of sales |  |  | (1,775 | ) |  |  | (2,035 | ) |  |  | — |  |  |  | (3,810 | )
Gross margin |  |  | 1,010 |  |  |  | 1,665 |  |  |  | — |  |  |  | 2,675 |
Selling, general and administrative |  |  | — |  |  |  | — |  |  |  | (3,594 | ) |  |  | (3,594 | )
Research and development |  |  | — |  |  |  | — |  |  |  | (646 | ) |  |  | (646 | )
Income (loss) from operations |  | $ | 1,010 |  |  | $ | 1,665 |  |  | $ | (4,240 | ) |  | $ | (1,565 | )
|  | Air Pollution |  |  | FUEL CHEM |  |  |  |  |  |  |  |  |
Three months ended June 30, 2025 |  | Control Segment |  |  | Segment |  |  | Other |  |  | Total |
Revenues from external customers |  | $ | 2,505 |  |  | $ | 3,053 |  |  | $ | — |  |  | $ | 5,558 |
Cost of sales |  |  | (1,406 | ) |  |  | (1,623 | ) |  |  | — |  |  |  | (3,029 | )
Gross margin |  |  | 1,099 |  |  |  | 1,430 |  |  |  | — |  |  |  | 2,529 |
Selling, general and administrative |  |  | — |  |  |  | — |  |  |  | (3,347 | ) |  |  | (3,347 | )
Research and development |  |  | — |  |  |  | — |  |  |  | (490 | ) |  |  | (490 | )
Income (loss) from operations |  | $ | 1,099 |  |  | $ | 1,430 |  |  | $ | (3,837 | ) |  | $ | (1,308 | )
|  | Air Pollution |  |  | FUEL CHEM |  |  |  |  |  |  |  |  |
Six months ended June 30, 2026 |  | Control Segment |  |  | Segment |  |  | Other |  |  | Total |
Revenues from external customers |  | $ | 4,389 |  |  | $ | 8,176 |  |  | $ | — |  |  | $ | 12,565 |
Cost of sales |  |  | (2,764 | ) |  |  | (4,482 | ) |  |  | — |  |  |  | (7,246 | )
Gross margin |  |  | 1,625 |  |  |  | 3,694 |  |  |  | — |  |  |  | 5,319 |
Selling, general and administrative |  |  | — |  |  |  | — |  |  |  | (7,310 | ) |  |  | (7,310 | )
Research and development |  |  | — |  |  |  | — |  |  |  | (1,170 | ) |  |  | (1,170 | )
Income (loss) from operations |  | $ | 1,625 |  |  | $ | 3,694 |  |  | $ | (8,480 | ) |  | $ | (3,161 | )
|  | Air Pollution |  |  | FUEL CHEM |  |  |  |  |  |  |  |  |
Six months ended June 30, 2025 |  | Control Segment |  |  | Segment |  |  | Other |  |  | Total |
Revenues from external customers |  | $ | 3,808 |  |  | $ | 8,132 |  |  | $ | — |  |  | $ | 11,940 |
Cost of sales |  |  | (2,284 | ) |  |  | (4,168 | ) |  |  | — |  |  |  | (6,452 | )
Gross margin |  |  | 1,524 |  |  |  | 3,964 |  |  |  | — |  |  |  | 5,488 |
Selling, general and administrative |  |  | — |  |  |  | — |  |  |  | (6,688 | ) |  |  | (6,688 | )
Research and development |  |  | — |  |  |  | — |  |  |  | (1,060 | ) |  |  | (1,060 | )
Income (loss) from operations |  | $ | 1,524 |  |  | $ | 3,964 |  |  | $ | (7,748 | ) |  | $ | (2,260 | )
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Geographical Area, Revenue and Long-Lived Asset [Table Text Block] |
|  | Three Months Ended |  |  | Six Months Ended |
|  | June 30, |  |  | June 30, |
|  | 2026 |  |  | 2025 |  |  | 2026 |  |  | 2025 |
Revenues: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
United States |  | $ | 5,901 |  |  | $ | 4,442 |  |  | $ | 11,148 |  |  | $ | 9,801 |
Foreign |  |  | 584 |  |  |  | 1,116 |  |  |  | 1,417 |  |  |  | 2,139 |
|  | $ | 6,485 |  |  | $ | 5,558 |  |  | $ | 12,565 |  |  | $ | 11,940 |
|  | June 30, |  |  | December 31, |
|  | 2026 |  |  | 2025 |
Assets: |  |  |  |  |  |  |  |
United States |  | $ | 40,636 |  |  | $ | 44,345 |
Foreign |  |  | 2,558 |  |  |  | 2,834 |
|  | $ | 43,194 |  |  | $ | 47,179 |

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