Use of an unmanned aircraft system to quantify NO _x emissions from a natural gas boiler

Aerial emission sampling of four natural gas boiler stack plumes was conducted using an unmanned aerial system (UAS) equipped with a lightweight sensor–sampling system (the “Kolibri”) for measurement of nitrogen oxide (NO), and nitrogen dioxide (NOinline-formula₂), carbon dioxide (COinline-formula₂), and carbon monoxide (CO). Flights (inline-formulan inline-formula= 22) ranged from 11 to 24 min in duration at two different sites. The UAS was maneuvered into the plumes with the aid of real-time COinline-formula₂ telemetry to the ground operators and, at one location, a second UAS equipped with an infrared–visible camera. Concentrations were collected and recorded at 1 Hz. The maximum COinline-formula₂, CO, NO, and NOinline-formula₂ concentrations in the plume measured were 10 000, 7, 27, and 1.5 ppm, respectively. Comparison of the NOinline-formula_x emissions between the stack continuous emission monitoring systems and the UAS–Kolibri for three boiler sets showed an average of 5.6 % and 3.5 % relative difference for the run-weighted and carbon-weighted average emissions, respectively. To our knowledge, this is the first evidence of the accuracy performance of UAS-based emission factors against a source of known strength.