Mobile Optical Remote Sensing for quantification of Ammonia and Methane emissions from Dairy Farms in California.

<p>Solar occultation flux (SOF) and Mobile extractive FTIR (MeFTIR) are techniques used for over 20 years to quantify industrial emissions of VOCs, CH<sub>4</sub>, and others, from refineries in the USA, Europe, and Asia. Here, they were combined to assess methane (CH<sub>4</sub>) and ammonia (NH<sub>3</sub>) from concentrated animal feeding operations (CAFOs) in the San Joaquin Valley (SJV), California. SOF and MeFTIR were used to measure NH<sub>3</sub> column, and ground concentrations of NH<sub>3</sub> and CH<sub>4</sub>, respectively. SOF retrieves the gas column concentration from the solar spectra using a solar track, directing the light to a FTIR spectrometer, while crossing the gas plume. Subsequently, a direct flux approach combines the retrieved columns with wind information to obtain the mass fluxes of ammonia. In this survey, the wind information was acquired by a wind LIDAR, which measures wind speed and direction in the interval of 10 – 300 m. On the other hand, Methane emissions were quantified using a unique indirect flux approach by combining the estimated ammonia fluxes and the NH<sub>3</sub>:CH<sub>4</sub> ratios measured from the ground concentration using MeFTIR.</p><p>Two field campaigns performed in spring and autumn studied emissions from 14 single dairy CAFOs. The daily emissions from the single farms averaged 96.4 ± 38.4 kg<sub>NH3 </sub>h<sup>-1</sup>and 411 ± 185.4 kg<sub>CH4</sub>h<sup>-1</sup>, respectively, for NH<sub>3</sub> and CH<sub>4</sub> with the corresponding emission factors (EF) per animal unit of 11.3 ± 3.8 g<sub>NH3</sub>h<sup>-1</sup>AU<sup>-1</sup>and 50.3 ± 24.1 g<sub>CH4</sub>h<sup>-1</sup>AU<sup>-1</sup>. The uncertainty of ammonia measurements was 17 % in a standard confidence interval (CI) and 37 % in a 95 % CI, with the largest uncertainty associated with the wind measurements. Furthermore, the methane uncertainty estimations averaged 27 % in a standard CI, and 52 % in a 95 % CI, dominated by the ammonia fluxes uncertainty. Comparison between Annual or daily EFs obtained by SOF to other quantification approaches, have to take into consideration the SOF measurement conditions, day-time and sunny weather, due to their effects on the NH<sub>3</sub> emissions. The study contributed to develop the knowledge of dairy CAFOs emission, and to strengthen the role of optical remote sensing techniques, bridging the gap between satellites and stationary measurement approaches.</p>