YAKIMA, Wash. — Farm fertilizers and manure at dairies might be sources of ammonia contributing to high levels of nitrate in Yakima air, a state Department of Ecology spokeswoman says.

But further study of how agricultural ammonia and nitrogen from motor vehicles mix in the air under certain weather conditions is needed before solutions can be considered, said Camille St. Onge, DOE communications manager in Olympia.

“It’s not just as straight forward as let’s just reduce ammonia or nitrogen. It’s the way they form in the air,” St. Onge said.

Whether further study will occur and how long it might take are not known as DOE just released results of a three-week, January 2013 study that determined high nitrate levels most likely are caused by agricultural ammonia and motor vehicle nitrogen interacting during certain weather conditions, she said. The study was done by Washington State University and Central Washington University researchers with DOE oversight.

High nitrate levels account for up to 30 percent of the fine-particle pollution in the Yakima area but less than 5 percent in other areas of the state, St. Onge said.

The Yakima level risks violating a federal 24-hour fine-particle pollution standard, DOE said in a news release. Fine-particle pollution, when breathed deeply, can lodge in lungs and cause structural and chemical changes and can act as carriers for other toxic and cancer-causing materials, DOE said.

Fine-particle pollution is particles of soot, dust and unburned fuel suspended in air, DOE said. Most of it in the Yakima area comes from wood burning and fine-particle pollution is greatest in winter due to more wood burning and weather conditions, DOE said.

Aerosol nitrate is an ingredient of fine-particle pollution and forms when ammonia and oxides of nitrogen react under the right weather conditions, DOE said.

EPA will ask DOE to put a plan in place to reduce pollution if the federal standard is violated, St. Onge said.

Indoor and outdoor burn bans to control fine-particle pollution from wood burning have been effective and are issued by the Yakima Regional Clean Air Agency, St. Onge said.

But nitrate is harder to control because it is not directly released by any one source, DOE said. To control it, a better understanding of its origin is needed, DOE said. There are large amounts of ammonia involved and the mixing with nitrogen in certain weather is complex chemistry, the department said.

When the air is still and cold, pollution in the Lower Yakima Valley does not have much effect on air quality in the upper valley and vice versa, DOE said.