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Data from bi-weekly passive samplers from 18 of the longest operating National Atmospheric Deposition Program’s (NADP) Ammonia Monitoring Network (AMoN) sites (most operating from 2008 to 2015) show that concentrations of NH 3 have been increasing (p-value < 0.0001) over large regions of the USA. This trend is occurring at a seasonal and annual level of aggregation. Using random coefficient models (RCM), the mean slope for the 18 sites combined shows an increase of NH 3 concentration of +7% per year, with a 95% confidence interval (C.I.) from +5% to +9% per year. Travel blank corrected data using the same approach show increasing NH 3 concentrations of +9% (95% C.I. +5% to +13%) per year. During a comparable period (2008–2014) NADP precipitation chemistry sites in the same regions show significant increasing (p-value = 0.0001) precipitation NH 4 + concentrations trends for all sites combined of +5% (95% C.I. +3% to +7%) per year. Emissions inventory data for the study period show nearly constant rates of NH 3 emissions, but large reductions in NOx and SO 2 emissions. Seasonal air quality data from the Clean Air Status and Trends Network (CASTNET) sites in these regions show significant declines in atmospheric particulate SO 4 2− and NH 4 + , and particulate NO 3 − plus HNO 3 (total NO 3 − ) during the same period. Less formation of acidic SO 4 and NO 3 , due to reduced SO 2 and NOx emissions, provide less substrate to interact with NH 3 and form particulate ammonium species. Thus, concentrations of NH 3 can increase in the atmosphere even if emissions remain constant. A likely result may be more localized deposition of NH 3 , as opposed to the more long-range transport and deposition of ammonium nitrate (NH 4 NO 3 ) and sulfate (NH 4 ) 2 SO 4 ). Additionally, the spatial distribution of wet and dry acidic deposition will be impacted. [ABSTRACT FROM AUTHOR]

Abstract: A miniaturized method based on liquid-phase microextraction (LPME) in combination with microvolume UV–vis spectrophotometry for monitoring ammonia in waters is proposed. The methodology is based on the extraction of the ion pair formed between the blue indophenol obtained according to the Berthelot reaction and a quaternary ammonium salt into a microvolume of organic solvent. Experimental parameters affecting the LPME performance such as type and concentration of the quaternary ammonium ion salt required to form the ion pair, type and volume of extractant solvent, effect of disperser solvent, ionic strength and extraction time, were optimized. A detection limit of 5.0μgL−1 ammonia and an enrichment factor of 30 can be attained after a microextraction time of 4min. The repeatability, expressed as relative standard deviation, was 7.6% (n =7). The proposed method can be successfully applied to the determination of trace amounts of ammonia in several environmental water samples. [ABSTRACT FROM AUTHOR]

An ammonia traces analyser based on photoacoustic spectroscopy is described. The system uses a CO2 laser and a properly designed resonant photoacoustic cell to achieve ammonia detection at sub-parts-per-billion (ppb) level. The instrument features unattended automatic on-line monitoring of ammonia with a detection limit of 0.1 ppb. Interferences from atmospheric CO2 and H2O are efficiently suppressed by a careful selection of the laser wavelength and a compensation of the water vapour signal made with a high-precision hygrometer. The cell design enables continuous measurement at high flow rates (up to 5 l/min), which guarantees a fast response time of the system for the monitoring of ammonia, a sticky polar molecule that adheres to most surfaces. Various examples of applications of the instrument in the semiconductor industry and for atmospheric pollution monitoring are presented. They demonstrate the excellent performances of the system and its suitability for these applications. [Copyright &y& Elsevier]