Photochemistry of NH2NO2 and implications for chemistry in the atmosphere

Recent studies have indicated that nitramide (NH₂NO₂) may be formed more plentifully in the atmosphere than previously thought, while also being a missing source of the greenhouse gas nitrous oxide (N₂O) via catalyzed isomerization. To validate the importance of NH₂NO₂ in the Earth's atmosphere, the ground and first electronic excited states of NH₂NO₂ were characterized and its photochemistry was investigated using multireference and coupled cluster methods. NH₂NO₂ is non-planar and of singlet multiplicity in the ground state while exhibiting large out-of-plane rotation in the triplet first excited state. One-dimensional cuts of the adiabatic potential energy surface calculated using the MRCI+Q method show low-lying singlet electronic states with minima in their potential along the N-N and N-O bond coordinates. Due to vertical excitation energies in the 225-180 nm region, photochemical processes will not compete in the troposphere, causing N₂O production to be the predicted major removal process of NH₂NO₂. In the upper atmosphere, photodissociation to form NH₂NO + O (³P) is suggested to be a major photochemical removal pathway.

Quantum Cascade Laser Measurements of Line Intensities, N2-, O2- and Ar- Collisional Broadening Coefficients of N2O in the ν3 Band Near 4.5 µm

This study deals with precise measurements of absolute line intensities, N2-, O2- and Ar- collisional broadening coefficients of N2O in the P-branch of the ν3 vibrational band near 4.5 µm. Collisional broadening coefficients of N2O-air are derived from the N2- and O2- broadening contributions by considering an ideal atmospheric composition. Studies are performed at room temperature for 10 rotational transitions over 2190-2202 cm(-1) spectral range using a distributed-feedback quantum cascade laser. To retrieve spectroscopic parameters for each individual transition, measured absorption line shape is simulated within Voigt and Galatry profiles. The obtained results compare well with previous experimental data available in the literature: the discrepancies being less than 4% for most of the probed transitions. The spectroscopic data reported here are very useful for the design of sensors used to monitor the abundance of N2O in earth's atmosphere.

Evaluation of leachate recirculation on nitrous oxide production in the Likang Landfill, China

Landfill leachate recirculation is efficient in reducing the leachate quantity handled by a leachate treatment plant. However, after land application of leachate, nitrification and denitrification of the ammoniacal N becomes possible and the greenhouse gas nitrous oxide (N2O) is produced. Lack of information on the effects of leachate recirculation on N2O production led to a field study being conducted in the Likang Landfill (Guangzhou, China) where leachate recirculation had been practiced for 8 yr. Monthly productions and fluxes of N2O from leachate and soil were studied from June to November 2000. Environmental and chemical factors regulating N2O production were also accessed. An impermeable top liner was not used at this site; municipal solid waste was simply covered by inert soil and compacted by bulldozers. A high N2O emission rate (113 mg m-2 h-1) was detected from a leachate pond purposely formed on topsoil within the landfill boundary after leachate irrigation. A high N2O level (1.09 micrograms L-1) was detected in a gas sample emitted from topsoil 1 m from the leachate pond. Nitrous oxide production from denitrification in leachate-contaminated soil was at least 20 times higher than that from nitrification based on laboratory incubation studies. The N2O levels emitted from leachate ponds were compared with figures reported for different ecosystems and showed that the results of the present study were 68.7 to 88.6 times higher. Leachate recirculation can be a cost-effective operation in reducing the volume of leachate to be treated in landfill. However, to reduce N2O flux, leachate should be applied to underground soil rather than being irrigated and allowed to flow on topsoil.

Exchange of Materials Between Terrestrial Ecosystems and the Atmosphere

Many biogenic trace gases are increasing in concentration or flux or both in the atmosphere as a consequence of human activities. Most of these gases have demonstrated or potential effects on atmospheric chemistry, climate, and the functioning of terrestrial ecosystems. Focused studies of the interactions between the atmosphere and the biosphere that regulate trace gases can improve both our understanding of terrestrial ecosystems and our ability to predict regional-and global-scale canges in atmospheric chemistry.