An uncertainty methodology for solar occultation flux measurements: ammonia emissions from livestock production

Ammonia (NH 3 ) emissions can negatively affect ecosystems and human health, so they should be monitored and mitigated. This study presents methodology for the estimation of uncertainties in NH 3 emissions measurements using the solar occultation flux (SOF) method. The reactive nature of NH 3 makes its measurement challenging, but SOF offers a reliable open-path passive method which utilizes solar spectrum data, thereby avoiding gas adsorption within the instrument. To compute NH 3 gas fluxes, horizontal and vertical wind speed profiles, as well as plume height estimates and spatially resolved column measurements, are integrated. A unique aspect of this work is the first-time description of plume height estimations derived from ground and column NH 3 concentration measurements aimed at uncertainty reduction. Initial validation tests indicated measurement errors between - 31 % and + 14 % on average, which was slightly larger than the estimated expanded uncertainty ranging from +/- 12 % to +/- 17 %. Application of the methodology to assess emission rates from farms of various sizes showed uncertainties between +/- 21 % and +/- 37 %, generally influenced by systematic wind uncertainties and random errors. The method demonstrates the capacity to measure NH 3 emissions from both small ( similar to 0.5-1 kg h - 1 ) and large ( similar to 100 kg h - 1 ) sources in high-density farming areas. Generally, the SOF method provided an expanded uncertainty below 30 % in measuring NH 3 emissions from livestock production, which could be further improved by adhering to best application practices. This paper's findings offer the potential for broader applications, such as measuring NH 3 fluxes from fertilized fields and in the oil and gas sector. However, these applications would require further research to adapt and refine the methodologies for these specific contexts.