Summertime HONO concentrations were synchronously measured at two (an agricultural and a non-agricultural) sites in the North China Plain (NCP). Daytime HONO (1.4±0.6 ppbv) and HONO/NO2 ((12±8)%) over the agricultural field after fertilization were found to be remarkably higher than those before fertilization, implying strong HONO emission from the fertilized fields.Synchronous enhancements of HONO and O3 after fertilization at both sites suggested that the emitted HONO accelerated the local and the regional O3 pollution. HONO budget analysis further revealed that its emission was significantly enhanced after fertilization. Soil HONO emission flux and its uncertainty were estimated and discussed. The estimated emission flux exhibited a distinct diurnal variation with a noontime maximum. Net OH production rate from HONO photolysis greatly exceeded that from O3 photolysis over the agricultural field, and their maximum ratio of 4.7 was obtained after fertilization. We provide field evidence that fertilized fields in the NCP act as a strong HONO source, which accelerates daytime photochemistry, leading to an increase of regional photo-oxidants such as O3. Considering the severe O3 pollution in the summer NCP and that the large area of the agricultural field is regularly treated with high fertilization amount in this region, HONO emission should be taken into account in the regional air quality deterioration.

Physical chemistryPhysical chemistry Z 0225 Kinetics and Mechanisms of the Oxidation of Oxygenated Organic Compounds in the Gas Phase -[161 refs.]. -(MELLOUKI*, A.; LE BRAS, G.; SIDEBOTTOM, H.; Chem. Rev. (Washington, D. C.) 103 (2003) 12, 5077-5096; Lab. Combust. Syst. React., CNRS, Univ. Orleans, F-45071 Orleans, Fr.; Eng.) -Lindner 10-287

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Abstract. An important fraction of secondary organic aerosol (SOA) formed by atmospheric oxidation of diverse volatile organic compounds (VOC) has recently been shown to consist of high-molecular weight oligomeric species. In our previous study (Sadezky et al., 2006), we reported the identification and characterization of oligomers as main constituents of SOA from gas-phase ozonolysis of small enol ethers. These oligomers contained repeated chain units of the same chemical composition as the main Criegee Intermediates (CI) formed during the ozonolysis reaction, which were CH2O2 (mass 46) for alkyl vinyl ethers (AVE) and C2H4O2 (mass 60) for ethyl propenyl ether (EPE). In the present work, we extend our previous study (Sadezky et al., 2006) to another enol ether (ethyl butenyl ether EBE) and a variety of structurally related small alkenes (trans-3-hexene, trans-4-octene and 2,3-dimethyl-2-butene). Experiments have been carried out in a 570 l spherical glass reactor at atmospheric conditions in the absence of seed aerosol. SOA formation was measured by a scanning mobility particle sizer (SMPS). SOA filter samples were collected and chemically characterized off-line by ESI(+)/MS-TOF and ESI(+)/MS/MS-TOF, and elemental compositions were confirmed by ESI(+)/MS/MS-FTICR. The results for all investigated unsaturated compounds are in excellent agreement with the observations of our previous study (Sadezky et al., 2006). Analysis of the collected SOA filter samples reveal the presence of oligomeric compounds in the mass range 200 to 800 u as major constituents. The repeated chain units of these oligomers are shown to systematically have the same chemical composition as the respective main Criegee Intermediate (CI) formed during ozonolysis of the unsaturated compounds, which is C3H6O2 (mass 74) for ethyl butenyl ether (EBE), trans-3-hexene, and 2,3-dimethyl-2-butene, and C4H8O2 (mass 88) for trans-4-octene. Analogous fragmentation pathways among the oligomers formed by gas-phase ozonolysis of the different alkenes and enol ethers in our present and previous study (Sadezky et al., 2006), characterized by successive losses of the respective CI-like chain unit as a neutral fragment, indicate a similar principal structure. As in our previous work (Sadezky et al., 2006), we suggest the basic structure of a linear oligoperoxide -[CH(R)-O-O]n- for all detected oligomers, with the repeated chain unit CH(R)OO corresponding to the respective major CI. Furthermore, copolymerization of CI simultaneously formed in the gas phase from two different unsaturated compounds is shown to occur during the ozonolysis of a mixture of trans-3-hexene and ethyl vinyl ether (EVE), leading to formation of oligomers with mixed chain units C3H6O2 (mass 74) and CH2O2 (mass 46). We therefore suggest oligoperoxide formation to be a general, so far unknown reaction pathway of small stabilized CI in the gas phase, which represents an alternative way to high-molecular products and thus contributes to SOA formation.

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In this chapter we consider the chemical changes induced by absorption of sunlight by oxygenated organic compounds. In contrast to the hydrocarbons, sunlight absorption by the oxygenated products of hydrocarbon oxidation shows a shift in absorption to the longer wavelengths such that their photodecompositions can become important atmospheric processes. This is illustrated in the absorption data given for methane and its oxidation products in figure IX-A-1. As a H3C—H bond in methane is replaced with a H3C—OH bond (alcohols), H3C—OCH3 bond (ethers), or H3C—O2H bond (hydroperoxides), light absorption involving excitation of nonbonding O-atom electrons to an antibonding sigma orbital (n → σ* transitions) becomes possible. These “forbidden” absorptions are smaller than the allowed σ → σ*transitions in the CH4 and the other alkanes, but the absorption bands are shifted to longer wavelengths progressing from CH4 to CH3OH, CH3OCH3, and CH3OOH as less energy is required to excite the nonbonding electron to the σ* orbital.

First principles calculations, by means of the full-potential linearized augmented plane wave method within the local density approximation, were carried out for the electronic and optical properties of the filled tetrahedral compounds LiMgN, LiMgP and LiMgAs. The bandgap trend in the ternaries is found to be similar to the one encountered in the zinc-blende AlX. The assignment of the structures in the optical spectra and band structure transitions are investigated in detail. The predicted values of the dielectric constants for LiMgN, LiMgP and LiMgAs are close to those of the binary compounds AlN, AlP and AlAs.

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