Note 11 - Business Segment and Geographic Financial Data (Tables)

9 Months Ended

Sep. 30, 2025

Notes Tables

Schedule of Segment Reporting Information, by Segment [Table Text Block]

	Air Pollution			FUEL CHEM
Three months ended September 30, 2025	Control Segment			Segment			Other			Total
Revenues from external customers	$	2,707		$	4,783		$	—		$	7,490
Cost of sales		(1,428	)		(2,401	)		—			(3,829	)
Gross margin		1,279			2,382			—			3,661
Selling, general and administrative		—			—			(3,207	)		(3,207	)
Research and development		—			—			(450	)		(450	)
Operating income (loss) from operations	$	1,279		$	2,382		$	(3,657	)	$	4

	Air Pollution			FUEL CHEM
Three months ended September 30, 2024	Control Segment			Segment			Other			Total
Revenues from external customers	$	3,224		$	4,627		$	—		$	7,851
Cost of sales		(2,095	)		(2,349	)		—			(4,444	)
Gross margin		1,129			2,278			—			3,407
Selling, general and administrative		—			—			(3,225	)		(3,225	)
Research and development		—			—			(361	)		(361	)
Operating income (loss) from operations	$	1,129		$	2,278		$	(3,586	)	$	(179	)

	Air Pollution			FUEL CHEM
Nine months ended September 30, 2025	Control Segment			Segment			Other			Total
Revenues from external customers	$	6,515		$	12,915		$	—		$	19,430
Cost of sales		(3,713	)		(6,568	)		—			(10,281	)
Gross margin		2,802			6,347			—			9,149
Selling, general and administrative		—			—			(9,895	)		(9,895	)
Research and development		—			—			(1,510	)		(1,510	)
Operating income (loss) from operations	$	2,802		$	6,347		$	(11,405	)	$	(2,256	)

	Air Pollution			FUEL CHEM
Nine months ended September 30, 2024	Control Segment			Segment			Other			Total
Revenues from external customers	$	9,491		$	10,359		$	—		$	19,850
Cost of sales		(5,927	)		(5,535	)		—			(11,462	)
Gross margin		3,564			4,824			—			8,388
Selling, general and administrative		—			—			(9,815	)		(9,815	)
Research and development		—			—			(1,159	)		(1,159	)
Operating income (loss) from operations	$	3,564		$	4,824		$	(10,974	)	$	(2,586	)

Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block]

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2025		2024		2025		2024
Revenues:
United States	$	5,626	$	5,453	$	15,427	$	13,519
Foreign		1,864		2,398		4,003		6,331
	$	7,490	$	7,851	$	19,430	$	19,850

	September 30,		December 31,
	2025		2024
Assets:
United States	$	44,917	$	44,430
Foreign		2,996		4,367
	$	47,913	$	48,797