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

6 Months Ended

Jun. 30, 2021

Notes Tables

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

	Air Pollution			FUEL CHEM
Three months ended June 30, 2021	Control Segment			Segment			Other			Total
Revenues from external customers	$	986		$	4,232		$	—		$	5,218
Cost of sales		(507	)		(2,128	)		—			(2,635	)
Gross margin		479			2,104			—			2,583
Selling, general and administrative		—			—			(2,957	)		(2,957	)
Research and development		—			—			(315	)		(315	)
Operating income (loss) from operations	$	479		$	2,104		$	(3,272	)	$	(689	)

	Air Pollution			FUEL CHEM
Three months ended June 30, 2020	Control Segment			Segment			Other			Total
Revenues from external customers	$	1,937		$	2,464		$	—		$	4,401
Cost of sales		(2,320	)		(1,479	)		—			(3,799	)
Gross margin		(383	)		985			—			602
Selling, general and administrative		—			—			(2,755	)		(2,755	)
Research and development		—			—			(271	)		(271	)
Operating (loss) income from operations	$	(383	)	$	985		$	(3,026	)	$	(2,424	)

	Air Pollution			FUEL CHEM
Six months ended June 30, 2021	Control Segment			Segment			Other			Total
Revenues from external customers	$	1,893		$	8,358		$	—		$	10,251
Cost of sales		(1,038	)		(4,272	)		—			(5,310	)
Gross margin		855			4,086			—			4,941
Selling, general and administrative		—			—			(6,057	)		(6,057	)
Research and development		—			—			(730	)		(730	)
Operating income (loss) from operations	$	855		$	4,086		$	(6,787	)	$	(1,846	)

	Air Pollution			FUEL CHEM
Six months ended June 30, 2020	Control Segment			Segment			Other			Total
Revenues from external customers	$	3,133		$	5,046		$	—		$	8,179
Cost of sales		(3,086	)		(2,964	)		—			(6,050	)
Gross margin		47			2,082			—			2,129
Selling, general and administrative		—			—			(6,641	)		(6,641	)
Research and development		—			—			(595	)		(595	)
Operating income (loss) from operations	$	47		$	2,082		$	(7,236	)	$	(5,107	)

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

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2021		2020		2021		2020
Revenues:
United States	$	4,588	$	3,310	$	9,051	$	6,407
Foreign		630		1,091		1,200		1,772
	$	5,218	$	4,401	$	10,251	$	8,179

	June 30,		December 31,
	2021		2020
Assets:
United States	$	46,186	$	24,524
Foreign		3,875		5,564
	$	50,061	$	30,088