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

9 Months Ended

Sep. 30, 2024

Notes Tables

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

	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
Three months ended September 30, 2023	Control Segment			Segment			Other			Total
Revenues from external customers	$	3,711		$	4,277		$	—		$	7,988
Cost of sales		(2,214	)		(2,162	)		—			(4,376	)
Gross margin		1,497			2,115			—			3,612
Selling, general and administrative		—			—			(2,966	)		(2,966	)
Research and development		—			—			(513	)		(513	)
Operating income (loss) from operations	$	1,497		$	2,115		$	(3,479	)	$	133

	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	)

	Air Pollution			FUEL CHEM
Nine months ended September 30, 2023	Control Segment			Segment			Other			Total
Revenues from external customers	$	10,692		$	10,044		$	—		$	20,736
Cost of sales		(7,155	)		(5,168	)		—			(12,323	)
Gross margin		3,537			4,876			—			8,413
Selling, general and administrative		—			—			(9,126	)		(9,126	)
Research and development		—			—			(1,144	)		(1,144	)
Operating income (loss) from operations	$	3,537		$	4,876		$	(10,270	)	$	(1,857	)

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,
	2024		2023		2024		2023
Revenues:
United States	$	5,453	$	5,640	$	13,519	$	15,937
Foreign		2,398		2,348		6,331		4,799
	$	7,851	$	7,988	$	19,850	$	20,736

	September 30,		December 31,
	2024		2023
Assets:
United States	$	45,789	$	46,487
Foreign		4,328		3,901
	$	50,117	$	50,388