Temperature Dependence Of NO Research Articles

Kinetics of NO and NO2Evolution from Illuminated Frozen Nitrate Solutions

The release of NO and NO2 from frozen aqueous NaNO3 irradiated at 313 nm was studied using time-resolved spectroscopic techniques. The kinetic behavior of NO and NO2 signals during on-and-off illumination cycles confirms that NO2 is a primary photoproduct evolving from the outermost ice layers and reveals that NO is a secondary species generated deeper in the ice, whence it eventually emerges due to its inertness and larger diffusivity. NO is shown to be more weakly held than NO2 by ice in thermal desorption experiments on preirradiated samples. The partial control of gaseous emissions by mass transfer, and hence by the morphology and metamorphisms of polycrystalline ice, is established by (1) the nonmonotonic temperature dependence of NO and NO2 signals upon stepwise warming under continuous illumination, (2) the fact that the NO, NO2 or NOx (NOx identical with NO + NO2) amounts released in bright thermograms performed under various heating ramps fail to scale with photon dose, due to irreversible losses in the adsorbed state. Because present NO/NO2 ratios are up to 10-fold smaller than those determined over sunlit snowpacks, we infer that the immediate precursors to NO mostly absorb at lambda > lambda(max) (NO3-) approximately 302 nm.

What controls photochemical NO and NO2 production from Antarctic snow? Laboratory investigation assessing the wavelength and temperature dependence

Laboratory experiments were conducted to determine the wavelength and temperature dependence of NO and NO2 release from Antarctic snow. This photochemically driven process has been observed during recent field measurements in polar regions. In this work the photochemical production of NO and NO2 was reproduced under laboratory conditions with NO2 dominating the production. The wavelength of incident light was varied over the range 295–385 nm. We observed a λ dependence where NO and NO2 release ceases when the snow was illuminated with λ > 345 nm. Comparing these data with the aqueous absorption cross section of the nitrate ion (NO3−) indicates that NO3− is the precursor N‐oxide species, which is photolyzed in snow. The temperature of the experimental system was varied over the range 253–243 K with no effect on NO and NO2 production. The occurrence of these photochemical processes followed by release to the atmosphere will impact the chemistry of the boundary layer over any snow‐covered region. In addition, understanding these processes is essential for accurate ice core interpretation.

Temperature dependence of NO to NO 2 conversion by n-butane and n-pentane oxidation

An experimental and detailed chemical kinetic modeling investigation of the temperature-dependentrole of n-butane and n-pentane oxidation on the NO to NO2 conversion is presented. An atmospheric pressure, quartz flow reactor was used to examine the NO oxidation to NO2 behavior for the 600 to 1100 K temperature range and residence times from 0.16 to 1.46 s. In the experiment, probe measurement of the species concentrations was performed in the flow reactor using a mixture of NO (20 ppm)/air/hydrocarbon (10 ppm). In the chemical kinetic calculation, the time evolution of NO, NO2, hydrocarbons, and reaction intermediates were evaluated using a n-butane oxidation model coupled with a nitrogen oxides submechanism for all temperatures. The detailed chemical kinetic model consisted of 897 reactions and 158 species. The experimental results show n-pentane promoting the NO to NO2 conversion to a greater extent thann-butane for the entire temperature range. This may be explained by n-pentane oxidation exhibiting a vigorous chain-branched hydroperoxy-pentylperoxy radical isomerization kinetic system more so than found in n-butane. Kinetic calculations performed on the n-butane oxidation system revealed that the NO to NO2 conversion is strongly temperature dependent. The NO+HO2=NO2+OH and alkylperoxy +NO=alkyloxy+NO2 reactions play an important role in converting NO to NO2 at the lower temperatures in this study. However, as the temperature increases toward 800–900 K, the butyl+O2 and hydroperoxy-butyl+O2 network of reactions undergoes reaction reversal and allows other reaction channels to be accessed which heavily promotes NO to NO2 conversion. Above 900 K, the decrease in NO2 concentration is attributed to NO2+HO2=HONO+O2, HONO(+M)=NO+OH(+M), and NO2+O=NO+O2 destruction reactions. Consequently, the change of HO2 formation with temperature plays the most important role for the temperature dependence of the NO to NO2 conversion.

Improved analysis of atmospheric absorption spectra by including the temperature dependence of NO2

Absorption spectra of NO2 measured at several temperatures between room temperature and 197 K are used to improve the analysis of zenith view, atmospheric absorption data in the 405–430 nm spectral range. The size of persistent features in the residual spectrum of the analysis is reduced by up to 50%, which in principle facilitates measurement of weakly absorbing species, such as OClO and IO. Details of the reduction algorithm are discussed.

Use of an optical probe for time-resolved in situ measurement of local air-to-fuel ratio and extent of fuel mixing with applications to low NOx emissions in premixed gas turbines

The lower temperatures associated with lean premixed combustion generally lead to lower NO x emissions; however, the benefit of lean premixed combustion may be lost if the fuel and air are poorly mixed. In this paper, we describe the development of an inexpensive fiber optic probe capable of measuring the extent of mixing. The fuel concentration is determined by laser light absorption at 3.39 μm over a short path length created by using infrared transmitting fiber optics. A hydrogen-piloted, CH 4 -in-air turbulent flame with a variable fuel injection location is used to vary the degree of mixedness at the burner exit. We use the optical probe to measure the level of mixedness (nonreacting) at the burner exit. The level of mixing and the mean concentration profiles are also measured by using planar laser-initiated Rayleigh scattering. NO x measurements are reported for several mixing distances. We show that at lean conditions (=0.6), incomplete mixing causes a dramatic increase in NO x production because of the exponential temperature dependence of NO x formation about =0.6. We also numerically investigate how the extent of mixing affects NO x production at various equivalence ratios and pressures. Modeling the effect of incomplete mixing on NO x formation is done with a distribution ofconvolved with numerical results from a perfectly stirred reactor in series with a plug flow reactor. The model does an excellent job of predicting the NO x increase caused by incomplete mixing at lean conditions. Model predictions at higher pressures that are typical of gas turbine conditions show good agreement with available data. In particular, for lean premixed combustion, NO x is not a function of pressure if the air and fuel are well mixed.

Structure of Opposed Jet Flame and NOx Formation.

High-intensity premixed combustion (0.71−1.12 × 10 9 kJ/m 3 h) was achieved using an opposed jet burner. The NO x emission was measured by an NO/NO x chemiluminescence analyzer. Maximum NO x formation measured was extremely low and varied from 20 ppm to 40 ppm, depending on the combustion intensity. Such a low NO x formation is attributed to the short residence time and the structure of the distributed reaction zone. The equivalence ratio at which NO x is maximized was found to be 1.3. The temperature dependence of NO x concentration can be given empirically by an Arrhenius expression, and the apparent activation energy is small compared with that of the Zel'dovich mechanism.

Electronic quenching rates for NO(A 2Σ +) measured in a shock tube

We report rate coefficients for electronic quenching of NO(A 2Σ +) by NO(X 2Π), CO 2, Ar and He measured at high temperature behind reproducible shock waves. NO and CO 2 are efficient quenchers at temperatures between 300 and 2100 K while the rare gases quench much less efficiently. We develop a model to predict the temperature dependence of NO(A 2Σ +) quenching by collision partners that have a large electron affinity and thereby enable a charge-transfer complex (NO +X −) to mediate the transition between the A 2Σ + ν′ =0 and X 2Π states of NO.