ACROSS_LISA_PRG_NH3_H2O_CH4_1-Min_L2

The atmospheric ammonia (NH3) concentration as volume mixing ratio was measured at the ground–based PRG urban site during ACROSS by a commercial in situ analyser (PROCEAS® NH3 from DURAG group, AP2E society, Aix-en-Provence, France), based on two technologies: Optical-Feedback Cavity-Enhanced Absorption Spectroscopy (OFCEAS) and low-pressure sampling. Air was taken from the sampling point (located on the roof of the Lamark B building of Paris Cité university at about 30 m height above the ground) to a common glass manifold of 4.3 dm3 volume (located about 10 m below, in the main building) by a teflon tube inlet of 17.5 mm inner diameter and 12 m length. The flow in this main line was fixed at 40 L min-1. The gas phase instruments sampled air from this common manifold. Data were acquired continuously at 10 sec time resolution then averaged to 1 minute. The time indicated in the datafile is the start time (UTC) of the 1-min interval. Available data started from June 12, 2022, until July 24, 2022. H2O and CH4 concentrations were simultaneously measured with ammonia as both species interfer in the NH3 spectral micro-window. They are therefore given as indicators of coherent data. Concentrations for NH3, H2O and CH4 are provided in ppb, % and ppb, respectively. Few data are missing between June 18, 2022 and June 20, 2022 due to an electrical disconnection. The data were not further calibrated since measuring ammonia with a standard is still challenging.