Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2009
Publication Date: 8/1/2009
Citation: Ro, K.S., Johnson, M.H., Varma, R.M., Hashmonay, R.A., Hunt, P.G. 2009. Measurement of greenhouse gas emissions from agricultural sites using open-path optical remote sensing method. Journal of Environmental Science and Health Part A 44(10):1011-1018. Interpretive Summary: Greenhouse gas emission into the atmosphere causes global warming. Agricultural sites such as livestock facilities are believed to be emission sources of the greenhouse gases. However, accurate measurement of the greenhouse gas emission from agricultural sites is extremely difficult because the emission rate depends on many factors such as wind speed and direction, terrain characteristics, greenhouse gas concentrations, etc. The use of a tunable diode laser greatly simplified the task of measuring gas concentrations in the air. However, several tunable diode lasers are needed along with wind speed and direction information in order to calculate emission rates of the greenhouse gases. Scientists at the USDA-ARS Coastal Plains Soil, Water & Plant Research Center, Florence, SC, recently improved this method using an automatic positioning device on which the tunable diode laser was attached. The positioning device directed the laser beam of the tunable diode laser to several mirrors downwind of emission sites. Use of this device eliminates the need for multiple tunable diode lasers which can be very expensive. The scientists conducted validation studies in which methane, a model greenhouse gas, was released from a simulated emission source at known rates. This new laser method was able to accurately measure the emission rates of methane. This new method can be readily applied to different gases such as ammonia and other greenhouse gases for improved estimates of emission rates from a variety of agricultural sources.
Technical Abstract: Improved characterization of distributed emission sources of greenhouse gases such as methane from concentrated animal feeding operations require more accurate methods. One promising method is recently used by the USEPA. It employs a vertical radial plume mapping (VRPM) algorithm using optical remote sensing techniques. We evaluated this method to estimate emission rates from simulated distributed methane sources. A scanning open-path tunable diode laser was used to collect path-integrated concentrations (PICs) along different optical paths on a vertical plane downwind of controlled methane releases. Each cycle consists of three ground-level PICs and two above ground PICs. Three- to 10-cycle moving averages were used to reconstruct mass equivalent concentration plum maps on the vertical plane. The VRPM algorithm estimated emission rates of methane along with meteorological and PIC data collected concomitantly under different atmospheric stability conditions. The derived emission rates compared well with actual released rates irrespective of atmospheric stability conditions. The maximum error was 22 percent when 3-cycle moving average PICs were used; however, it decreased to 11% when 10-cycle moving average PICs were used. Our validation results suggest that this new VRPM method may be used for improved estimations of emission rates from a variety of agricultural sources.