Particulate emissions from a beef cattle feedlot using the flux-gradient technique

Data on air emissions from open-lot beef cattle () feedlots are limited. This research was conducted to determine fluxes of particulate matter with an aerodynamic diameter ≤10 μm (PM) from a commercial beef cattle feedlot in Kansas using the flux-gradient technique, a widely used micrometeorological method for air emissions from open sources. Vertical PM concentration profiles and micrometeorological parameters were measured at the feedlot using tapered element oscillating microbalance PM samplers and eddy covariance instrumentations (i.e., sonic anemometer and infrared hygrometer), respectively, from May 2010 through September 2011, representing feedlot conditions with air temperatures ranging from -24 to 39°C. Calculated hourly PM fluxes varied diurnally and seasonally, ranging up to 272 mg m h, with an overall median of 36 mg m h. For warm conditions (air temperature of 21 ± 10°C), the highest hourly PM fluxes (range 116-146 mg m h) were observed during the early evening period, from 2000 to 2100 h. For cold conditions (air temperature of -2 ± 8°C), the highest PM fluxes (range 14-27 mg m h) were observed in the afternoon, from 1100 to 1500 h. Changes in the hourly trend of PM fluxes coincided with changes in friction velocity, air temperature, sensible heat flux, and surface roughness. The PM emission was also affected by the pen surface water content, where a water content of at least 20% (wet basis) would be sufficient to effectively reduce PM emissions from pens by as much as 60%.

Comparison of AERMOD and WindTrax dispersion models in determining PM10 emission rates from a beef cattle feedlot

Reverse dispersion modeling has been used to determine air emission fluxes from ground-level area sources, including open-lot beef cattle feedlots. This research compared Gaussian-based AERMOD, the preferred regulatory dispersion model of the US. Environmental Protection Agency (EPA), and WindTrax, a backward Lagrangian stochastic-based dispersion model, in determining PM10 emission rates for a large beef cattle feedlot in Kansas. The effect of the type of meteorological data was also evaluated. Meteorological conditions and PM10 concentrations at the feedlot were measured with micrometeorological/eddy covariance instrumentation and tapered element oscillating microbalance (TEOM) PM10 monitors, respectively, from May 2010 through September 2011. Using the measured meteorological conditions and assuming a unit emission flux (i.e., 1 microg/m2-sec), each model was used to calculate PM10 concentrations (referred to as unit-flux concentrations). PM10 emission fluxes were then back-calculated using the measured and calculated unit-flux PM10 concentrations. For AERMOD, results showed that the PM10 emission fluxes determined using the two different meteorological data sets evaluated (eddy covariance-derived and AERMET-generated) were basically the same. For WindTrax, the two meteorological data sets (sonic anemometer data set, a three-variable data set composed of wind parameters, surface roughness, and atmospheric stability) also produced basically the same PM10 emission fluxes. Back-calculated emission fluxes from AERMOD were 32 to 69% higher than those from WindTrax.

IMPLICATIONS

This work compared the PM10 emission rates determined from a large commercial cattle feedlot in Kansas by reverse dispersion modeling using AERMOD and WindTrax. Emission fluxes derived from AERMOD were greater than those from WindTrax by mean factors of 1.3 to 1.6. Based on the high linearity observed between the two models, emission fluxes derived from one dispersion model for the purpose of simulating dispersion could be applied to the other model using appropriate conversion factors.

Particulate matter emission rates from beef cattle feedlots in Kansas-reverse dispersion modeling

Open beef cattle feedlots emit various air pollutants, including particulate matter (PM) with equivalent aerodynamic diameter of 10 microm or less (PM10); however limited research has quantified PM10 emission rates from feedlots. This research was conducted to determine emission rates of PM10 from large cattle feedlots in Kansas. Concentrations of PM10 at the downwind and upwind edges of two large cattle feedlots (KS1 and KS2) in Kansas were measured with tapered element oscillating microbalance (TEOM) PM10 monitors from January 2007 to December 2008. Weather conditions at the feedlots were also monitored. From measured PM10 concentrations and weather conditions, PM10 emission rates were determined using reverse modeling with the American Meteorological Society/U.S. Environmental Protection Agency Regulatory Model (AERMOD). The two feedlots differed significantly in median PM10 emission flux (1.60 g/m2-day for KS1 vs. 1.10 g/m2-day for KS2) but not in PM10 emission factor (27 kg/1000 head-day for KS1 and 30 kg/1000 head-day KS2). These emission factors were smaller than published U.S. Environmental Protection Agency (EPA) emission factor for cattle feedlots.