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

3 Months Ended

Mar. 31, 2024

Notes Tables

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

	Air Pollution			FUEL CHEM
Three months ended March 31, 2024	Control Segment			Segment			Other			Total
Revenues from external customers	$	2,318		$	2,639		$	—		$	4,957
Cost of sales		(1,428	)		(1,500	)		—			(2,928	)
Gross margin		890			1,139			—			2,029
Selling, general and administrative		—			—			(3,345	)		(3,345	)
Research and development		—			—			(376	)		(376	)
Operating income (loss) from operations	$	890		$	1,139		$	(3,721	)	$	(1,692	)

	Air Pollution			FUEL CHEM
Three months ended March 31, 2023	Control Segment			Segment			Other			Total
Revenues from external customers	$	3,559		$	3,728		$	—		$	7,287
Cost of sales		(2,594	)		(1,888	)		—			(4,482	)
Gross margin		965			1,840			—			2,805
Selling, general and administrative		—			—			(3,245	)		(3,245	)
Research and development		—			—			(218	)		(218	)
Operating income (loss) from operations	$	965		$	1,840		$	(3,463	)	$	(658	)

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

	Three Months Ended
	March 31,
	2024		2023
Revenues:
United States	$	3,595	$	5,981
Foreign		1,362		1,306
	$	4,957	$	7,287

	March 31,		December 31,
	2024		2023
Assets:
United States	$	45,744	$	46,487
Foreign		3,702		3,901
	$	49,446	$	50,388