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

3 Months Ended

Mar. 31, 2023

Notes Tables

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

	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	)

	Air Pollution			FUEL CHEM
Three months ended March 31, 2022	Control Segment			Segment			Other			Total
Revenues from external customers	$	2,204		$	3,331		$	—		$	5,535
Cost of sales		(1,429	)		(1,816	)		—			(3,245	)
Gross margin		775			1,515			—			2,290
Selling, general and administrative		—			—			(3,054	)		(3,054	)
Research and development		—			—			(220	)		(220	)
Operating income (loss) from operations	$	775		$	1,515		$	(3,274	)	$	(984	)

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

	Three Months Ended
	March 31,
	2023		2022
Revenues:
United States	$	5,981	$	3,688
Foreign		1,306		1,847
	$	7,287	$	5,535

	March 31,		December 31,
	2023		2022
Assets:
United States	$	46,893	$	47,007
Foreign		3,389		3,117
	$	50,282	$	50,124