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

6 Months Ended

Jun. 30, 2025

Notes Tables

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

	Air Pollution			FUEL CHEM
Three months ended June 30, 2025	Control Segment			Segment			Other			Total
Revenues from external customers	$	2,505		$	3,053		$	—		$	5,558
Cost of sales		(1,406	)		(1,623	)		—			(3,029	)
Gross margin		1,099			1,430			—			2,529
Selling, general and administrative		—			—			(3,347	)		(3,347	)
Research and development		—			—			(490	)		(490	)
Operating income (loss) from operations	$	1,099		$	1,430		$	(3,837	)	$	(1,308	)

	Air Pollution			FUEL CHEM
Three months ended June 30, 2024	Control Segment			Segment			Other			Total
Revenues from external customers	$	3,949		$	3,093		$	—		$	7,042
Cost of sales		(2,405	)		(1,685	)		—			(4,090	)
Gross margin		1,544			1,408			—			2,952
Selling, general and administrative		—			—			(3,245	)		(3,245	)
Research and development		—			—			(422	)		(422	)
Operating income (loss) from operations	$	1,544		$	1,408		$	(3,667	)	$	(715	)

	Air Pollution			FUEL CHEM
Six months ended June 30, 2025	Control Segment			Segment			Other			Total
Revenues from external customers	$	3,808		$	8,132		$	—		$	11,940
Cost of sales		(2,284	)		(4,168	)		—			(6,452	)
Gross margin		1,524			3,964			—			5,488
Selling, general and administrative		—			—			(6,688	)		(6,688	)
Research and development		—			—			(1,060	)		(1,060	)
Operating income (loss) from operations	$	1,524		$	3,964		$	(7,748	)	$	(2,260	)

	Air Pollution			FUEL CHEM
Six months ended June 30, 2024	Control Segment			Segment			Other			Total
Revenues from external customers	$	6,267		$	5,732		$	—		$	11,999
Cost of sales		(3,833	)		(3,185	)		—			(7,018	)
Gross margin		2,434			2,547			—			4,981
Selling, general and administrative		—			—			(6,590	)		(6,590	)
Research and development		—			—			(798	)		(798	)
Operating income (loss) from operations	$	2,434		$	2,547		$	(7,388	)	$	(2,407	)

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,
	2025		2024		2025		2024
Revenues:
United States	$	4,442	$	4,471	$	9,801	$	8,066
Foreign		1,116		2,571		2,139		3,933
	$	5,558	$	7,042	$	11,940	$	11,999

	June 30,		December 31,
	2025		2024
Assets:
United States	$	44,130	$	44,430
Foreign		2,873		4,367
	$	47,003	$	48,797