HPLC-MS determination of the oxidation products of the reaction between alpha- and beta-pinene and OH radicals.

Biogenic non-methane hydrocarbons such as isoprene, alpha-pinene, and beta-pinene, are emitted by forests in very large quantities. To evaluate the role of alpha- and beta-pinene and their contribution to the global production of trace gases and especially aerosol precursors, a study of the oxidation mechanism of alpha- and beta-pinene with hydroxyl radicals must be conducted. The degradation products of both monoterpenes with hydroxyl radicals were identified and quantified in a fast-flow reactor. The products were collected on a liquid-nitrogen trap coated with a 2,4-DNPH solution to which two internal standards (benzaldehyde-2,4-DNPH and tolualdehyde-2,4-DNPH) had been added. The collection method was based on the in situ conversion of aldehyde and/or ketone compounds to their 2,4-dinitrophenylhydrazone derivatives. The derivatives were analyzed by HPLC-MS using APCI(-). TIC chromatograms and mass spectral data for the various oxidation products are presented. For alpha-pinene, pinonaldehyde is the most important degradation product, with smaller amounts of acetone, formaldehyde, campholenealdehyde, and acetaldehyde. For beta-pinene, nopinone and formaldehyde are the most abundant products, of almost equal importance, whereas acetone and acetaldehyde are minor compounds.

Determination of the oxidation products of the reaction between alpha-pinene and hydroxyl radicals by high-performance liquid chromatography.

In this paper a method is described for determining and quantifying the degradation products of the reaction of alpha-pinene with hydroxyl radicals. The study is carried out in a fast-flow reactor equipped with a specially designed microwave cavity (type Surfatron) allowing to operate at pressures up to 100 Torr (1 Torr=133.322 Pa). The semi-volatile products are collected on a liquid nitrogen trap (LN2 trap) coated with a 2,4-dinitrophenylhydrazine (2,4-DNPH) solution and the batch samples are subsequently analyzed by HPLC. In order to perform quantitative measurements the batch samples contained two internal standards: benzaldehyde-2,4-DNPH and tolualdehyde-2,4-DNPH. In the experiments carried out at 50 Torr and 100 Torr, HPLC measurements showed that the semi-volatile products formaldehyde, acetaldehyde, acetone, campholenealdehyde and pinonaldehyde could be quantified as oxidation products for the alpha-pinene/OH reaction, with pinonaldehyde being the main product. Assuming that all these five oxidation products have the same collection efficiency on the LN2 trap, one arrives at the following relative product yields (expressed in mol %) at 50 and 100 Torr, respectively: 9.7+/-0.7 and 6+/-5 for formaldehyde; 1.1+/-0.1 and 0.9+/-0.5 for acetaldehyde; 16+/-1 and 6+/-2 for acetone; 11+/-2 and 5.5+/-0.7 for campholenealdehyde; 63+/-3 and 82+/-7 for pinonaldehyde.

Identification of the oxidation products of the reaction between alpha-pinene and hydroxyl radicals by gas and high-performance liquid chromatography with mass spectrometric detection.

In this paper an identification method is described for determining the degradation products of the reaction of alpha-pinene with hydroxyl radicals. The study is carried out in a fast-flow reactor equipped with a specially designed microwave cavity (type Surfatron) allowing to operate at pressures up to 100 Torr (1 Torr=133.322 Pa). The semivolatile products are collected on a liquid nitrogen trap (LN2 trap) and the batch samples are subsequently analysed by GC-MS and HPLC-MS. Some samples were also collected directly on a LpDNPH-cartridge, followed by HPLC-MS analysis. When experiments were carried out at 50 Torr both GC-MS and HPLC-MS measurements showed that campholenealdehyde and pinonaldehyde were identified as condensable oxidation products for the alpha-pinene/OH reaction, with pinonaldehyde being the main product. Furthermore, the LN2 trap collection method based on the in situ conversion of aldehydes and ketones to their 2,4-dinitrophenylhydrazone derivatives allowed the determination of formaldehyde, acetaldehyde and acetone. Although formaldehyde and acetone are present in small amounts in blank samples it could be established that formaldehyde and acetone are also formed in the alpha-pinene/OH reaction.

Development and validation of a dynamic mathematical model of ammonia release in pig house.

A dynamic mathematical model of Carbon-dioxide Accelerated Ammonia Release (CAAR) was developed based on the known knowledge of the chemistry of ammonia (NH3) in liquid solution, mass transfer inside liquid and across liquid-gaseous interface, and a new concept of CAAR. It calculated the NH3 concentration, release and emission at transient and steady state conditions related to a mechanically ventilated pig house. One field experimental data set was used for estimating the proportionality coefficient in the model. Another field data set was used for model validation. The ammonia concentration and emission rate calculated in the model validation were compared with the field measurement values. R2 of 0.861 and 0.947 were obtained for NH3 concentration and emission rate, respectively. In the model validation, the pH in manure surface was found to increase from 8 at initial condition to 8.85 at dynamic equilibrium due to the co-release of CO2 from the manure. This pH change accelerated the NH3 release by 6.1-fold. The model provided a quantitative description of some new understanding of the mechanism of NH3 release in the pig house and entailed suggestions of two new techniques of NH3 emission abatement: the reduction of CO2 release and the new ventilation control strategy.

A new concept of carbon dioxide accelerated ammonia release from liquid manure in pig house.

Indoor air quality in animal buildings is very important to the health of agricultural workers and animals. Carbon dioxide (CO2) and ammonia (NH3) are two of the most important pollutants in pig houses. Four tests were conduced in a mechanically ventilated pig house to study release behaviors of CO2 and NH3 from liquid manure using impulse, pulse and step ventilation inputs. The CO2 and NH3 concentrations were sampled in the exhaust chimney and measured with a CO2 monitor and a NOx analyzer, respectively. The ventilation rate was measured with a ventilation rate sensor in the chimney. A new phenomenon, characterized by a delayed dynamic response of NH3 release to the high ventilation inputs as compared with the response of CO2 release, was encountered. A new CO2 factor was identified as the cause of the delayed NH3 response. An original concept of Carbon-dioxide Accelerated Ammonia Release (CAAR) was developed. It explained that, at the initial stage of gas release induced by the high ventilation, the high release of CO2 gradually raised the pH in the surface manure. The increased pH accelerated the release of NH3. The higher release of NH3 had a negative feedback to the pH. The effects of CO2 and NH3 releases on the pH finally reached a dynamic equilibrium. The NH3 release under the dynamic equilibrium was greatly accelerated compared to that under initial conditions.

The reaction of nitrite with the haemocyanin of the Roman snail (Helix pomatia).

The reaction of nitrite at pH 5.0-7.0 with the deoxyhaemocyanin of a mollusc, the Roman snail (Helix pomatia), yielded nitrosylhaemocyanin (CuIA.NO+ CuIIB), in contrast with the formation of methaemocyanin with the deoxyhaemocyanin of the crustacean Astacus leptodactylus (mud crayfish). With Helix haemocyanin 1 NO was thereby liberated per active site, as shown by m.s., as against 2 NO with Astacus haemocyanin. Helix nitrosylhaemocyanin was characterized in c.d. by the negative extremum at 336 nm (CuIA.NO+) and by the mononuclear e.p.r. signal at g = 2 (CuIIB). Binuclear e.p.r. signals have been observed after the addition of nitrite to methaemocyanins. With Astacus methaemocyanin, no further reaction occurred, whereas with Helix methaemocyanin the mononuclear e.p.r. signal, characteristic for nitrosylhaemocyanin gradually appeared. This formation of Helix nitrosylhaemocyanin implicates the binding, most likely on CuIIA, of a second nitrite besides a bridging nitrite, so that a dismutation into NO and NO2 can occur there. A further dismutation of NO2 yields nitrite and nitrate. The formation of the latter was demonstrated by Raman spectrometry. The reaction rate of Helix methaemocyanin with nitrite decreased with increasing pH according to the Henderson-Hasselbalch equation with a pKa value of 6.77, attributed to a mu-aquo bridging ligand, which can be exchanged for nitrite, in equilibrium with a mu-hydroxo ligand which cannot. These data also favour the formulation of the final reaction product as nitrosylhaemocyanin instead of semi-methaemocyanin, with or without bound nitrite.

The reaction of nitrogen monoxide with the haemocyanins of the crayfish Astacus leptodactylus and the snail Helix pomatia.

The rate of the reaction of Astacus leptodactylus methaemocyanin with NO follows the Henderson-Hasselbalch equation with a pKa of 5.85, suggesting that one imidazole ligand of Cu was exchanged for NO. The reaction is blocked by F- as a bridging ligand. The same imidazole residue might be responsible for the decomposition of nitrosylhaemocyanin, [Cu1NO+CuII], with an unlocated binding site for NO, into methaemocyanin and NO, as the rate increase with pH. NO could react preferentially with CuA of Helix pomatia methaemocyanin, CuA'IICuBII, as it possibly has only two histidine ligands instead of the three of CuA in Astacus haemocyanin. This difference might explain the higher formation rate and the much greater stability of Helix nitrosylhaemocyanin. The fast reaction is governed by a pKa of 6.80, probably of a bridging mu-aquo ligand. With F- or a mu-hydroxo bridging ligand a low reaction rate was still observed, in contrast with Astacus methaemocyanin. Helix nitrosylhaemocyanin was transformed by N3- into methaemocyanin with the liberation of N2 and N2O. This methaemocyanin could almost quantitatively be regenerated with H2O2. Helix nitrosylhaemocyanin was only partially regenerated by a direct treatment with H2O2 and almost quantitatively by HONH2 in a similar fairly fast reaction, followed by a much slower one.

The reaction of nitrite with the haemocyanin of Astacus leptodactylus.

The reaction of nitrite at pH 5.7 with deoxyhaemocyanin of Astacus leptodactylus yielded methaemocyanin in two one-electron steps, as nitrite was reduced to NO. This methaemocyanin could be almost fully regenerated by an anaerobic treatment with HONH2, in contrast with the methaemocyanin prepared with H2O2. A destruction of active sites on treating oxyhaemocyanin with HONH2 explains the partial regeneration of methaemocyanin under air, as traces of H2O2 are formed in the autoxidation of HONH2. The reaction rate of nitrite with deoxyhaemocyanin is almost 15 times that with oxyhaemocyanin. The slope of -1.0 for the logarithm of the pseudo-first-order rate constants plotted against pH indicates that HNO2 is the reacting species. Methaemocyanin was e.p.r.-undetectable, but a binuclear signal was observed at g = 2 on binding nitrite to methaemocyanin. This signal disappeared with a pKa of 6.50, suggesting that a mu-aquo bridging ligand, which can be replaced by nitrite, is deprotonated to a mu-hydroxo bridging ligand, which resists substitution by nitrite. The intensity of this triplet e.p.r. signal allowed the determination of the association constant of nitrite to the active site of Astacus methaemocyanin and yielded a value of 237 M-1 at pH 5.7. The interpretation by some authors of nitrosylhaemocyanin as a nitrite derivative of semimethaemocyanin is contradicted by this rapid reaction of nitrite with copper(I) in deoxyhaemocyanin and in semi-methaemocyanin and by the low binding constant of nitrite to the active site of methaemocyanin.