A haystack fire at a dairy east of Moxee contributed to poor air quality and a smell not unlike marijuana over the last two days, but conditions are expected to improve Thursday. Meanwhile, a burn ban is in effect.

The odiferous air was unmistakable. “It does have that same type of aroma,” said acting East Valley fire Chief Mike Riel.

A fire in 60 tons of hay at Devries Family Farms, off State Route 24 east of Moxee, was reported about 4 a.m. Monday. The smoldering fires can take days to fully extinguish because the bales have to be pulled apart.

Firefighters worked on the fire for several hours Monday before company employees took over the job.

People across Yakima reported the strong, pot-like smell starting Monday night. “I smelled it myself,” Yakima police Capt. Rod Light said.

Haystack fires are commonly caused by spontaneous combustion stemming from moisture within the bales.

A projected worsening of air quality late Tuesday and overnight prompted the Yakima Regional Clean Air Agency to impose stricter countywide burn limits. The agency called a stage 2 burn ban effective at 2:30 p.m.

Agency spokesman Dave Caprile said conditions were expected to deteriorate Tuesday evening. An inversion is trapping pollutants near the surface of the ground, raising health concerns for sensitive groups like infants and children, the elderly and those with respiratory problems.

A stage 2 ban prohibits all outdoor burning, including agricultural burning, and the use of all home wood-heating appliances unless the device is the home’s sole source of heat.

The ban does not cover the Yakama reservation, which is under the authority of the federal Environmental Protection Agency.

The agency said the burn ban will be re-evaluated today. Conditions are expected to improve by Thursday with the approach of a frontal system that will bring rain to the Valley and snow to the higher elevations.

Reporters Phil Ferolito and David Lester contributed to this report.

Mark Morey can be reached at 509-577-7671 or mmorey@yakimaherald.com.