|Parnell, Jr., Calvin|
Submitted to: Journal of Air and Waste Management Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2006
Publication Date: 1/2/2007
Citation: Wang, L., Parnell Jr, C.B., Buser, M.D. 2007. Theoretical study of the impact of particulate matter gravitational settling on ambient coarse particulate matter monitoring for agricultural emissions. Journal of the Air & Waste Management Association. 57:111-115. Interpretive Summary: Federal reference method PM10 samplers have an inherent sampling error due to the interaction of particle size distribution and sampler performance characteristics. This manuscript addresses changes in the particle size distribution of particulate matter in a downwind plume due to gravitation settling, and impacts of these changes on ambient PM10 sampler measurements. Gravitational settling greatly impacts downwind particle size distributions of particulate matter from agricultural emissions. However, PM10 sampler over-sampling rates increase as the distance from the source to the sampler increases. This is caused by a decrease in the geometric standard deviation of the particle size distribution of the particulate matter in the downwind plume, resulting from the larger particles settling out of the plume. This research shows that account for the gravitational settling of particles does not reduce the over-sampling problems associated with the EPA approved PM10 samplers.
Technical Abstract: The particle size distributions (PSD) of particulate matter (PM) in the downwind plume from simulated sources were analyzed to determine the impact of PM settling on PM monitoring. The PSD of PM in a plume varies as a function of gravitational settling.Gravitational settling has a greater impact on the downwind PSD from sources with PSDs with larger mass median diameters (MMD). The change in PSD is a function of the source PSD of emitted PM, wind speed, and downwind distance. Both MMD and geometric standard deviation (GSD) in the downwind plume decrease with an increase in downwind distance and source MMD. Sources that emit PM with larger MMDs will have larger changes in the downwind MMD and GSD. Also, as the distance from the source to the samplers increases the greater the change in the downwind MMD and GSD. Variations of the PSD in the downwind plume significantly impact PM10 sampling errors associated with the EPA PM10 samplers. The PM10 over-sampling rate increases with an increase in downwind distance caused by the decrease of the PSD GSD in the downwind plume. Gravitational settling of particles does not help reduce the over-sampling problems associated with the EPA PM10 sampler. Further, over-sampling rates decrease with an increase of the wind speed.