IPR ASSIGNMENT

IPR Assignment



IPR Assignment

Adsorption of various octenes and octanes was researched with a 10-membered ring molecular sieve, H-[B]ZSM-5. Adsorption of octane was very fast, the double-branched octane diffused gradually, and the triple-branched molecules could not go in the channels of the sample. Since the 10-membered ring molecular sieves are the best catalysts for skeletal isomerisation of n-butene, trimethylpentenes or other bigger oligomers will not be intermediates in this reaction. By compare, skeletal isomerisation of n-butane which is renowned to need 12-membered ring passages, can involve a trimethylpentane-like molecule as an intermediate. Their lifetimes under tropospheric conditions are calculated to range from a few minutes to a few hours. Their oxidation in the atmosphere has multiple impacts in both the gas and aerosol phases, in particular on the budget of tropospheric ozone, on the oxidizing capacity of the atmosphere and on the production of organic aerosols (IPCC, 2001). Since these biogenic emissions are controlled by temperature and light, they can be expected to change, and most probably to increase, in the future as a result of climate change (European Commission, 2003). Monoterpenes are important constituents of biogenic NMOC emissions. Although they account for 10-15% of the total biogenic NMOCs emissions worldwide (Guenther et al., 2000), they are still comparable in magnitude to the total anthropogenic NMOC emissions. Their atmospheric oxidation is an important source of acetone, which has been shown to be an important actor in upper tropospheric chemistry. Furthermore, their degradation yields low volatility compounds which readily form organic secondary aerosols (SOA). Recent estimates of the global aerosol production from biogenic precursors (mostly terpenes) are in the range 2.5-79 Tgyr-1. This production might be influenced by human activities, e.g. through the impact of anthropogenic emissions on the levels of the terpene oxidants, or on the organic aerosol concentration.

Amongst the monoterpenes, -pinene is observed to have the highest emission rates and to be the most abundant. Several experimental studies have investigated the formation of gas-phase products from its oxidation by OH. The yield of pinonaldehyde has been estimated to range from 28 to 87% in presence of NO and between 3 and 37% in absence of NO. The experimental yields of acetone range from 4 to 11% in presence of NO (and has been estimated to about 15% in absence of NO. Pinonaldehyde and acetone yields of 82% and 6% respectively, at 100 torr. The large discrepancies between these various studies may be related to differences in the measurement techniques, in the way the yields are estimated from concentrations, and in the photochemical conditions in the reactor. Whereas the chemistry of simple hydrocarbons is relatively well understood the degradation of large NMOCs is more difficult, due to the large number of reactions involved and to the scarceness of direct laboratory investigations of these reactions. Jenkin et al. (1997) described the development of a near-explicit chemical mechanism (Master Chemical Mechanism, MCM) describing the detailed gas-phase degradation of a series of NMOCs. Its construction is based on relatively simple rules describing the kinetics ...