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Open-lot, concentrated animal feeding operations (CAFOs) in the southern High Plains, such as cattle feed-yards and open-lot dairies, emit fugitive particulate matter (PM) that occasionally reduces downwind visibility. The long-path visibility transmissometer (LPV) can be used to measure changes in total atmospheric extinction, a direct measure of path-averaged visibility impairment. To our knowledge, no researchers have used transmissometry as a surrogate to estimate aerosol concentrations downwind of open-lot livestock facilities. We compare time-resolved PM mass concentrations (µg m-3) and atmospheric extinction coefficients (km-1) measured simultaneously along the downwind boundary of a commercial cattle feedyard to compute "extinction efficiency," the change in atmospheric extinction that results from a unit change in PM mass concentration. Expected values for the in-situ extinction efficiency of total suspended particulate (TSP) and its fraction less than 10 microns (PM10) aerodynamic equivalent diameter (AED) are 0.2 to 0.5 m² g-1 and 0.4 to 0.8 m² g-1, respectively. Determination of the atmospheric extinction efficiency of feedyard dust will enable transmissometry to be used as an intuitive, real-time surrogate for measuring time-averaged PM10 and/or TSP concentrations. [ABSTRACT FROM AUTHOR]

Mixing ratios of total and gaseous ammonia were measured at an open-air cattle feeding facility in the Texas Panhandle in the summers of 2007 and 2008. Samples were collected at the nominally upwind and downwind edges of the facility. In 2008, a series of far-field samples was also collected 3.5 km north of the facility. Ammonium concentrations were determined by two complementary laboratory methods, a novel application of visible spectrophotometry and standard ion chromatography (IC). Results of the two techniques agreed very well, and spectrophotometry is faster, easier, and cheaper than chromatography. Ammonia mixing ratios measured at the immediate downwind site were drastically higher (approximately 2900 parts per billion by volume [ppbv]) than thos measured at the upwind site (< or = 200 ppbv). In contrast, at 3.5 km away from the facility, ammonia mixing ratios were reduced to levels similar to the upwind site (< or = 200 ppbv). In addition, PM10 (particulate matter < 10 microm in optical diameter) concentrations obtained at each sampling location using Grimm portable aerosol spectrometers are reported. Time-averaged (1-hr) volume concentrations of PM10 approached 5 x 10(12) nm3 cm(-3). Emitted ammonia remained largely in the gas phase at the downwind and far-field locations. No clear correlation between concentrations of ammonia and particles was observed. Overall, this study provides a better understanding of ammonia emissions from open-air animal feeding operations, especially under the hot and dry conditions present during these measurements.