Ag, burning, cold nights add up to poor air quality

By Tina Hilding, College of Engineering & Architecture

Yakima-air-80YAKIMA, Wash. – A new Washington State University study has found that a combination of agricultural emissions, human-based activity – like running car engines and burning woodstoves – and cold, still winter nights adds up to poorer air quality in the Yakima Valley than in much of the state.

air-monitoring-trailer-200Working in collaboration with the Yakima Regional Clean Air Agency, Yakama Nation, state Department of Ecology and Central Washington University, the WSU researchers found that ammonia from agricultural activities and emissions from motor vehicles lead to high pollution levels under specific cold and stagnant atmospheric conditions during winter.

Researchers conducted the study at the request of the ecology department after that agency’s routine monitoring picked up elevated levels of nitrate particles in the air in the Yakima area. The agency monitors air pollutants throughout Washington to ensure federal health-based air quality standards are met.

When breathed deep into the lungs, fine particle pollution can lodge and cause structural and chemical changes. These particles can also act as carriers for other toxic and cancer-causing materials. Recent air monitoring data showed that the Yakima region had high levels of atmospheric nitrates and could risk violating federal standards (PM2.5) for fine particle pollution.

air-monitoring-equipment-in-trailer-200“On some winter nights, the pollution levels in the Yakima Valley can reach what the EPA (U.S. Environmental Protection Agency) says are unhealthy levels,’’ said Tim VanReken, assistant professor in the WSU Department of Civil and Environmental Engineering.

With a sophisticated atmospheric chemistry laboratory housed in a custom-built trailer, the researchers took careful measurements throughout the region and created a detailed data set in January 2013. The results are much more detailed than typical air quality monitoring that is conducted by state agencies.

The researchers found that, under the right conditions, a significant amount of locally-released ammonia along with emissions from human activities contribute to the formation of nitrates in the air. Ammonia emissions can come from agricultural activities and byproducts, such as fertilizer and animal urine. Ammonia reacts in the atmosphere to become part of the nitrate particulate matter.

air-monitoring-250The researchers also found that the air pollution is generated locally rather than being transported from elsewhere.

“The Yakima Valley emissions dominated the air quality picture,’’ said VanReken.

The researchers believe that because of the large amount of ammonia emissions in the region and the complex chemistry involved, reducing levels of nitrate will be difficult.

The WSU research team is now using computer models to better understand and gather more evidence about the effect of various emission reduction strategies.



Tim VanReken, assistant professor, WSU Department of Civil and Environmental Engineering, 509-335-5055,

Tina Hilding, communications coordinator, WSU College of Engineering and Architecture, 509-335-5095,