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Title: Aerosol sampling: Comparison of two rotating impactors for field droplet sizing and volumetric measurements

item Fritz, Bradley - Brad
item Hoffmann, Wesley

Submitted to: Journal of the American Mosquito Control Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2009
Publication Date: 12/20/2009
Citation: Barber, J., Greer, M., Fritz, B.K., Hoffmann, W.C. 2009. Aerosol sampling: Comparison of two rotating impactors for field droplet sizing and volumetric measurements. Journal of the American Mosquito Control Association. 25:474-479.

Interpretive Summary: Application efficacy of mosquito control sprays is highly dependent on droplet size and on the amount of spray aloft in the area of application. Field assessment of both of these factors is currently very difficult as the application areas are very large requiring a large number of samplers. The currently used standard sampler is expensive with a low droplet collection efficiency. This research details a new sampling device that collects approximately 2.5 times the volume of spray as compared with the current standard. Further, with the use of appropriate corrections for operational inefficiencies, the new sampler can be used to estimate both the volume of spray aloft as well as droplet size of the spray. This sampling method, coupled with mosquito control studies, will help optimize mosquito control sprays and lead to improved application methodologies.

Technical Abstract: This paper compares the collection characteristics of a new rotating impactor for ultra fine aerosols (FLB) with the industry standard (Hock). The volume and droplet size distribution collected by the rotating impactors were measured via spectroscopy and microscopy. The rotary impactors were co-located with an iso-kinetic air sampler for a total volume flux measure and a Sympatec laser for droplet size distribution measure. Comparisons were made across three different wind speeds 1m/s 1.8 m/s and 3.5m/s to ascertain whether wind speed affected collection efficiency. The spray volume per unit area was higher with the FLB sampler as a function of collection efficiency. The FLB sampler was not significantly affected by wind speed change and returned more consistent data. The Hock was significantly affected by wind speed and erratically collected droplets in the smaller droplet size bins. Droplet size classes between 9 and 25 micrometers produced data similar to previous research. Some of the commonly used calculations of collection efficiency are considered. The results for the two different samplers are presented and their practical use discussed.