Novel mobile measurements of ammonia and methane: distinguishing agricultural and traffic sources in the Netherlands

<jats:p>Abstract. A mobile atmospheric measurement platform combining an open-path ammonia (NH₃) analyzer (HT‑8700E) and a closed-path tunable infrared laser direct absorption spectroscopy (TILDAS) multi-gas system was deployed to enable simultaneous, high-frequency observations of NH₃, methane (CH₄), and carbon monoxide (CO) under real-world conditions. The open-path configuration minimizes inlet-related artefacts and enables fast-response NH₃ measurements. A comprehensive measurement framework is presented, including instrument integration, field calibration and validation using co-located reference measurements, data synchronization, plume identification, background removal, and plume-integrated enhancement analysis. The performance of the platform was evaluated during a 160 km mobile campaign in the Veluwe region of the Netherlands, a Natura 2000 nature reserve surrounded by intensive livestock farming. During the campaign, plumes from 49 individual sources and approximately 630 transient traffic-related events were detected, resolving short-lived concentration enhancements across agricultural, industrial, and traffic-dominated environments. Plume-integrated enhancement ratios (ΣNH₃:ΣCH₄) showed systematic differences among source types, with low ratios for livestock farms (∼0.04 for cattle and goats), intermediate values for industrial sources, and substantially higher ratios for manured fields (&gt;2) and traffic plumes (&gt;4). In addition, NH₃ emission factors derived for traffic increased with driving speed from approximately 0.12 g kg⁻¹ fuel at low speeds to ~0.28 g kg⁻¹ under highway conditions. These results demonstrate that simultaneous mobile measurements of NH₃, CH₄, and CO provide an effective approach for detecting and differentiating emission sources under real-world conditions. The combined observations reveal distinct source signatures and potential gaps in existing emission inventories. Although uncertainties remain due to atmospheric variability, calibration, limited temporal sampling, and overlap in source-specific ratios, the methodology shows strong potential for high-resolution characterization of heterogeneous NH₃ emissions through repeated mobile monitoring campaigns.</jats:p>