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Rate coefficients for the reaction of NO3 radicals with a series of aromatic aldehydes were measured in a 7300 L simulation chamber at ambient temperature and pressure by relative and absolute methods. The rate coefficients for benzaldehyde (BA), ortho-tolualdehyde (O-TA), meta-tolualdehyde (M-TA), para-tolualdehyde (P-TA), 2,4-dimethyl benzaldehyde (2,4-DMBA), 2,5-dimethyl benzaldehyde (2,5-DMBA) and 3,5-dimethyl benzaldehyde (3,5-DMBA) were k₁= 2.6 ± 0.3, k₂= 8.7 ± 0.8, k₃= 4.9 ± 0.5, k₄= 4.9 ± 0.4, k₅= 15.1 ± 1.3, k₆= 12.8 ± 1.2 and k₇= 6.2 ± 0.6, respectively, in the units of 10^-15 cm³ molec.^-1 s^-1 at 298 ± 2 K. The ratemore » coefficient k₁₃ for the reaction of the NO₃ radical with deuterated benzaldehyde (benzaldehyde-d1) was found to be half that of k₁. The end product of the reaction in an excess of NO₂ was measured to be C₆H₅C(O)O₂NO₂. Furthermore, theoretical calculations of aldehydic bond energies and reaction pathways indicate that the NO₃ radical reacts primarily with aromatic aldehydes through the abstraction of an aldehydic hydrogen atom. The atmospheric implications of the measured rate coefficients are briefly discussed.« less

Nitrous oxide (N₂O) is currently the most important ozone-depleting substance emission and is a potent greenhouse gas. It is also a remarkably unreactive chemical species. Any loss processes for N₂O in the troposphere and combustion can be important. Therefore, as part of an effort to investigate how N₂O reacts with prototypical chemical species, its reaction with singlet methylene (CH₂) is studied here using high accuracy thermochemistry mHEAT-345(Q) calculations, together with two-dimensional (E,J) master equation simulations. Two distinct mechanisms (an addition/elimination and an O-abstraction) have been characterized. The reaction is found to be very fast with a negative temperature dependence.

The effect of an increase in atmospheric aerosol concentrations on the distribution and radiative properties of Earth’s clouds is the most uncertain component of the overall global radiative forcing from pre-industrial time. General Circulation Models (GCMs) are the tool for predicting future climate, but the treatment of aerosols, clouds, and aerosol-cloud radiative effects carries large uncertainties that directly affect GCM predictions, such as climate sensitivity. Predictions are hampered by the large range of scales of interaction between various components that need to be captured. Observation systems (remote sensing, in situ) are increasingly being used to constrain predictions but significant challengesmore » exist, to some extent because of the large range of scales and the fact that the various measuring systems tend to address different scales. Fine-scale models represent clouds, aerosols, and aerosol-cloud interactions with high fidelity but do not include interactions with the larger scale and are therefore limited from a climatic point of view. Lastly, we suggest strategies for improving estimates of aerosol-cloud relationships in climate models, for new remote sensing and in situ measurements, and for quantifying and reducing model uncertainty.« less