Application of an atmospheric tracer ratio method to estimation of PM_2.5 emission rates from wheat conveying operations at a wheat pile storage facility

ABSTRACT

Particulate matter (PM) pollution is associated with adverse effects on human health and the environment. There is no designated PM_2.5 emission factor for horizontal grain conveyors. Instead, in Washington state, the air permitting agency uses an emission factor for headhouse and grain handling operations to issue permits. There is concern that this factor does not accurately represent the conveyor operations and limits the size and operation of wheat pile facilities. The primary goal of this work was to estimate the PM_2.5 emission rate (which can further be converted to an emission factor) from wheat conveying operations at a large wheat pile storage facility in eastern Washington using an atmospheric tracer ratio method, with CO₂ gas as the tracer. The field study results yield an emission rate of 5.2$\pm$1.7 grams of PM_2.5 per hour and these emissions are due to the transfer point from an upper belt to a lower belt. This rate is approximately 320 times lower than the emission rate for headhouse operations which has been used previously to represent conveyor operations. The emission rate was in relatively good agreement with results of an inverse Gaussian plume model calculation of emissions using measured ambient PM_2.5 levels at a very short distance downwind of the transfer point. A consistent PM_2.5 to tracer gas ratio over the tests showed that PM_2.5 and CO₂ disperse in a similar manner and confirmed that the CO₂ tracer release was a reliable simulation of the PM_2.5 pollutant source over distances involved in the study (less than 10 meters). The results also indicate a need for the Environmental Protection Agency to develop a designated PM_2.5 emission factor for wheat conveyance.

Implications

There are presently no emission factors available for large wheat pile storage facilities where wheat is transferred via long horizontal conveyor belts. As a result, local and state permitting agencies use emission factors for other types of grain handling systems. In this paper, we report the first measurements of PM_2.5 emission rates (that can further be converted to emission factors using a known grain rate on the conveyor) for horizontal grain conveyors used at wheat pile storage facilities. The measured emission rate is much less than the emission rate derived from the surrogate emission factor currently used for permit purposes. This has implications for the size and operation of wheat pile storage facilities.

Acknowledgment

This study was funded by the Ritzville Warehouse Company. The authors acknowledge Brian Gordon for the opportunity of conducting the experiments, David Kommes for arranging for the field experiments, and Scott Somers for coordination of the field experiments and providing comments on technical aspects of the study. The authors acknowledge the assistance of Patrick O’Keeffe in designing the experiments and providing necessary training. The authors also thank Adriana Carbon and Kristina Koh for their collaboration in conducting the experiments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Ritzville Warehouse Company.

Notes on contributors

Anna Potapova

Anna Potapova is a research assistant in the Department of Civil and Environmental Engineering at Washington State University, Pullman, WA.

Brian Lamb

Brian Lamb is Regents Professor Emeritus in the Laboratory for Atmospheric Research and Department of Civil and Environmental Engineering at Washington State University, Pullman, WA.

Candis Claiborn

Candis Claiborn is Professor and Dean Emeritus in the Voiland College of Engineering and Architecture at Washington State University, Pullman, WA.