This paper describes the sensor technology, measurement methodology and data analysis algorithms that are used to characterize gaseous emissions observed with a large-area coverage longwave-infrared (LWIR) hyperspectral imaging (HSI) sensor. In so doing the demonstrated capability is expanded well beyond the small number of gas species that have typically been reported and also sets these observations within a definitive, comprehensive framework that documents in detail the procedures used for detection, identification, and quantification of atmospheric trace gases using LWIR HSI systems, along with the methodology for determining their respective detection limits. Examples are provided for a 530km2 region of the Los Angeles Basin collected on July 22, 2014. •Theory and practice of gas remote sensing with airborne LWIR HSI.•Large area survey (530km2) of Los Angeles Basin searched for gaseous effluents.•186 distinct plume sources (22 chemicals) located within the collected region.