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

3 Months Ended

Mar. 31, 2022

Notes Tables

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

	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	)

	Air Pollution			FUEL CHEM
Three months ended March 31, 2021	Control Segment			Segment			Other			Total
Revenues from external customers	$	907		$	4,126		$	—		$	5,033
Cost of sales		(531	)		(2,144	)		—			(2,675	)
Gross margin		376			1,982			—			2,358
Selling, general and administrative		—			—			(3,100	)		(3,100	)
Research and development		—			—			(415	)		(415	)
Operating income (loss) from operations	$	376		$	1,982		$	(3,515	)	$	(1,157	)

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

	Three Months Ended
	March 31,
	2022		2021
Revenues:
United States	$	3,688	$	4,463
Foreign		1,847		570
	$	5,535	$	5,033

	March 31,		December 31,
	2022		2021
Assets:
United States	$	46,142	$	46,271
Foreign		3,479		3,703
	$	49,621	$	49,974