The determination of ammonia in ambient air by an automated thermodenuder system

Quartz-enhanced photoacoustic NH3 sensor exploiting a large-prong-spacing quartz tuning fork and an optical fiber amplifier for biomedical applications

A sensor system for exhaled ammonia (NH₃) monitoring exploiting quartz-enhanced photoacoustic spectroscopy (QEPAS) was demonstrated. An erbium-doped fiber amplifier (EDFA) with an operating frequency band targeting an NH₃ absorption line falling at 1531.68 nm and capable to emit up to 3 W of optical power was employed. A custom T-shaped grooved QTF with prong spacing of 1 mm was designed and realized to allow a proper focusing of the high-power optical beam exiting the EDFA between the prongs. The performance of the realized sensor system was optimized in terms of spectrophone parameters, laser power and modulation current, resulting in a NH₃ minimum detectable concentration of 14 ppb at 1 s averaging time, corresponding to a normalized noise equivalent absorption coefficient (NNEA) of 8.15 × 10^-9 cm^-1 W/√Hz. Continuous measurements of the NH₃ level exhaled by 3 healthy volunteers was carried out to demonstrate the potentiality of the developed sensor for breath analysis applications.

Extração de amônio de filtros de amostragem, coleta e determinação pelo método da gota suspensa

A amostragem de amônia no ar é feita usualmente com filtro impregnado com ácido. O ácido ascórbico, quando usado como impregnante, é facilmente oxidado em meio básico e aquoso, gerando uma solução fortemente colorida que inviabiliza a determinação por colorimetria. Este trabalho apresenta um novo procedimento para extração do íon amônio dos filtros de amostragem, transferindo o íon amônio para uma gota de solução contendo ácido sulfúrico 0,1 mol L-1. A amostra do filtro é inicialmente solubilizada com água. A solução é colocada dentro de uma câmara com posterior adição de solução de NaOH 1,5 mol L-1. Com a ajuda de com borbulhamento de nitrogênio, a amônia formada passa para a fase gasosa, sendo finalmente recolhida para uma gota de ácido sulfúrico. A esta gota é adicionado um reagente e o produto determinado colorimetricamente pela reação do indofenol. Além da eliminação de interferentes, o procedimento apresenta a vantagem de fazer uma nova pré-concentração da amônia, possibilitando melhorar o limite de detecção do método de determinação.

Chemical composition of the NH3-HNO 3-H 2SO 4-NaCl system in the atmosphere of Athens, Greece

This paper presents a procedure for estimating the distribution of ionic material in the NH3-HNO3-H2SO4-NaCl system and applies this procedure in a particular case. The data used were measurements of HNO3, NH3, NO 3 (-) , SO 4 (-) , NH 4 (+) Cl(-) and Na(+) performed during February 1989 - February 1990 in a central Athens street with high traffic density. According to the procedure, ions combine in the following manner: Na(+) combines preferentially with SO 4 (-) , then with NO 3 (-) , followed by NH 4 (+) with the remaining SO 4 (-) and then with the remaining NO 3 (-) to form bisulphates, sulphates and nitrates. The combination procedure showed that the main constituents of the NH3-HNO3-H2SO4-NaCl system are primarily (NH4)2SO4 and, to a lesser extent, NH4NO3 and NH4HSO4, with mean and maximum concentrations, during morning hours, (NH4)2SO4: 14.5 (max 46.8), NH4NO3: 2.97 (max 23) and NH4HSO4: 1.78 (max 40.6) µg m(-3). Lower concentations of Na2SO4, NaHSO4, NaNO3 and NH4Cl and very low concentrations of H2SO4 are also present, depending on the availability of NaCl. It became apparent from the ionic distribution that there is sufficient NH3 to neutralize the H2SO4 and HNO3. It was also shown that a significant fraction of the HNO3, especially on days with high pollution, occurs as aqueous NO 3 (-) . A number of empirical equations have been proposed, which enable the approximate estimation of the constituents of the NH3-HNO3-H2SO4-NaCl system from air pollution monitoring data and meteorological parameters.

Delayed NH3 and N2 O uptake by maize leaves

¹⁵ N was used to give evidence of NH₃ and N₂ O absorption by maize leaves. A short-term labelling method (90 min) was chosen with high NH₃ concentration (40 μ1 1^-1 ) to assess uptake mechanisms. Two initial entry pathways were suggested for NH₃ : fast uptake with immediate metabolism and fast storage with progressive metabolism. A storage compartment delayed NH₃ absorption after exposure. Similar mechanisms might be involved in N₂ O uptake.

Measurement of dry deposition of ammonia on a forest

Ammonia concentration gradients above a Douglas fir canopy were measured from 16 August to 31 December 1989 by two automated high-precision thermodenuders at the location Speulderbos in The Netherlands. Concentration gradients were used to calculate the dry deposition flux of ammonia via flux-gradient theory. Meteorological data were obtained from a nearby tower. Ammonia concentrations were highly variable with highest values during the night. Concentration gradients were very small during daytime and quite large at night. Median values of the calculated deposition flux and deposition velocity were 0.1 microg m(-2) s(-1) and 3.2 cm s(-1) respectively (N=1624).