Atmospheric reactivity

Methane and the Nonmethane Hydrocarbons. It is traditional to distinguish CH4 from all other atmospheric hydrocarbons. Methane is by far the most abundant atmospheric hydrocarbon and has very large natural emissions. Its abundance in auto exhaust but low atmospheric reactivity has led air pollution scientists to enact controls on nonmethane hydrocarbons NMHC (also called VOC for volatile organic compounds, which include oxygenated hydrocarbons). 

A definition based upon the NMHC concentration might require nonmethane hydrocarbons to contribute insignificantly to atmospheric reactivity. Such a region might still contain very low concentrations of nonmethane hydrocarbons, so long as their sum total reactivity does not significantly contribute to that of methane and carbon monoxide. This is to say, in clean air... 

Grimsrud, E. P., H. H. Westberg, and R. A. Rasmussen. Atmospheric reactivity of monoterpene hydrocarbons, NOs photooxidation and ozonolysis. Int. J. Chem. Kinet. Symp. 1 (Chemical Kinetics Data for the Lower and Upper Atmosphere) 183-195, 1975. 

Maynard, J. B., and W. N. Sanders. Determination of the detailed hydrocarbon compontion and potential atmospheric reactivity of foil-range motor gasolines. J. Air PoUut. Control Assoc. 19 505-510, 1%9. 

Russell, A., J. Milford, M. S. Bergin, S. McBride, L. McNair, Y. Yang, W. R. Stockwell, and B. Croes, Urban Ozone Control and Atmospheric Reactivity of Organic Gases, Science, 269, 491-495... 

Stutz J, Ackermann R, Fast JD, Barrie L (2002) Atmospheric Reactive Chlorine and Bromine at the Great Salt Lake, Utah. Geophys Res Lett 29 1380... 

OH reaction is experimentally known, the information for the Cl reaction is new. For the OH reaction, the hydrogen atom is preferred while the reaction with Cl atoms both a and p hydrogen are favored. This suggests that the oxidation byproducts of n-bromopropane is going to be different for the OH versus Cl initiation chemistry. The results presented in this computational study should provide useful insight for modeling n-bromopropane global cycle in atmospheric reactivity models. 

Stutz J., Ackermann R., Fast J. D., and Barrie L. (2002) Atmospheric reactive chlorine and bromine at the Great... 

TA can be run in either a reactive or non-reactive atmosphere. Reactive atmospheres include corrosive, oxidizing and reducing gases. Non-reactive atmospheres should be an inert gas with little water vapor. Dry Ar and N2 are commonly used for non-reactive atmospheres. Gas flows through the furnace tube around the sample and carries volatile products out. A flow rate of 15-25 ml min-1 is recommended for a sample mass of about 2-10 mg. 

Many different types of volatile organic compounds (VOCs) are emitted into the atmosphere, where they can affect photochemical ozone formation and other measures of air quality. Because they can react in the atmospheres at different rates and with different mechanisms, the different types of VOCs can vary significantly in their effects on air quality. The effect of a VOC on ozone formation in a particular environment can be measured by its incremental reactivity , which is defined as the amount of additional ozone formed when a small amount of the VOC is added to the environment, divided by the amount added. Although this can be measured in environmental chamber experiments, incremental reactivities in such experiment cannot be assumed to be the same as incremental reactivities in the atmosphere (Carter and Atkinson, 1989 Carter et al, 1995). This is because it is not currently practical to duplicate in an experiment all the environmental factors that affect relative reactivities and, even if it were, the results would only be applicable to a single type of environment. The only practical means to assess atmospheric reactivity, and how it varies among different environments, is to estimate its atmospheric ozone impacts using airshed models. 

Becker, K.H. (ed.) Influence of fuel formulation on atmospheric reactivity of exhaust gases (INFORMATEX), final report of the EC project, contract N° ENV4-CT95-0015, Wuppertal (1998) (see also http //www.physchem.uni-wuppertal.de/PC-WWW Site/Publications/Publications.html). 

Furthermore, chemical models to be developed can be applied in the EUROCHAMP network for the solution of specific problems in atmospheric chemistry, e.g. development and validation of degradation mechanisms of organic pollutants that are of paramount importance, the investigation of atmospheric reactivity as an overall property under various conditions or the influence of alternative fuels or solvents as well as bio fuels on tropospheric chemistry (3 objective). 

Atmospheric Aerosols, is in atmospheric reactivity of sea-salt aerosols and urban air pollution control. Measurements of pollutants, physical and chemical modelling of secondary pollutants production and propagation in the urban and rural areas are performed. 

Gas-phase photochemical studies of the important components of atmospheric reactive nitrogen, peroxyacetyl nitrate (PAN, MeC(0)00N02) and per-oxypropionyl nitrate (PPN, EtC(0)00N02), have been carried out. Quantum yields for the formation of NO3 were determined for 248 and 308 nm irradiation, and absorption cross sections determined for PPN between 200 and 340 nm over the temperature range 253-296 K. 

Oxygenated hydrocarbons can be added to gasoline to replace traditional gasoline hydrocarbon components in an effort to lower the atmospheric reactivity of automotive tailpipe and evaporative emissions. Oxygenates that are currently being added to gasolines or are being... 

All the experiments described above give strong indications for the atmospheric reactivity of several PAH with gaseous pollutants or with oxygen in the presence of light. However, in these simulation experiments, both the particle material and the exposure conditions used are often chosen as a function of the available experimental facilities. Thus, simplifications are Introduced (choice of carrier, use of single PAH, etc.) which are certainly appropriate for fundamental studies, but make it difficult to extrapolate kinetic data obtained in laboratory exposures to the actual gas-aerosol chemistry in the atmosphere. 

N.A. Kelly andP. Wang, (1996) Part 1 Indoor Smog Chamber Study of Reactivity in Kelly, N.A. Wang, P. Japar, S.M. Hurley, M.D. and WaUington, T.L (1996). Measurement of the Atmosphere Reactivity of Emissions from Gasoline and Alternative-Fueled Vehicles Assessment of Available Methodologies, Second-Year Final Report, CRC Contract No. AQ-6-1-92 and NREL Contract No. AF-2-112961. Environmental Research Consortium, (September). 

The chief pathways to account for the disappearance of MTBE in the environment are atmospheric reactions and biodegradation. By virtue of its sterically hindered structure, MTBE has lower reactivity than other hydrocarbons in gasoline. The atmospheric half-life of MTBE has been estimated at 4 toll days (Carter et al., 1991). MTBE will react with hydroxyl (OH) radicals in the atmosphere. The rate of atmospheric reactivity of hydroxyl radicals with MTBE has been determined to be close to 2.8 x 10 cm molecule sec . While the ultimate product of degradation of MTBE is carbon dioxide and water, in laboratory experiments, observed products are tertiarybutyl formate, formaldehyde, methyl acetate, and acetone. Organic nitrate has also been noted when nitrogen oxides are present. 

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