Remote troposphere chemistry

To treat the chemistry of oxides of nitrogen, which play such a central role in the chemistry of both the polluted and remote troposphere, in a consistent manner, we have discussed the formation and fates of... 

Although only 10% of atmospheric ozone resides in the troposphere (0-15 km altitude) it has a profound impact on tropospheric chemistry. Ozone concentrations in the troposphere vary from typically 20-40 ppb for a remote pristine site to 100-200 ppb in a highly polluted urban environment. Ozone is a reactive molecule, which readily adds to carbon-carbon double bonds [8]. Reaction with ozone provides an important removal mechanism for many unsaturated reactive organic compounds. 

An analogous split between NOj -sensitive and NOjc-saturated chemistry occurs in the remote troposphere, but the implications are somewhat different. Increased CO and VOCs always contribute to increased ozone in the remote troposphere, even under NO -sensitive conditions (Jaegle et at, 1998, 2001), whereas ozone in polluted regions with NOj -sensitive chemistry is largely insensitive to CO and VOCs. 

Historically the study of urban air pollution and its effects occurred more or less separately from that of the chemistry of the Earth s atmosphere as a whole. Similarly, in its early stages, climate research focused exclusively on CO2, without reference to effects on the underlying chemistry of the atmosphere and their feedbacks on climate itself. It is now recognized, in quantitative scientific terms, that the Earth s atmosphere is a continuum of spatial scales in which the urban atmosphere, the remote troposphere, the marine boundary layer, and the stratosphere are merely points from the smallest turbulent eddies and the fastest timescales of free-redical chemistry to global circulations and the decadal timescales of the longest-lived trace gases. 

PAN/NOy, a fact that we will return to later when we discuss tropospheric chemistry. Indeed, PAN is the most abundant NOy species in the remote free troposphere. 

Penkett, S. A. 1982. Non-methane organics in the remote troposphere. In E. D. Goldberg, ed.. Atmospheric chemistry. Springer, Berlin, pp. 329-355. 

A40. Cmtzen, P.J., 1990 Global Changes in Tropospheric Chemistry , Proceedings of Summer School on Remote Sensing and the Earth s Environment, Alpbach, Austria, 26 July-4 August 1989, pp. 105-113. 

When NMHC are significant in concentration, differences in their oxidation mechanisms such as how the NMHC chemistry was parameterized, details of R02-/R02 recombination (95), and heterogenous chemistry also contribute to differences in computed [HO ]. Recently, the sensitivity of [HO ] to non-methane hydrocarbon oxidation was studied in the context of the remote marine boundary-layer (156). It was concluded that differences in radical-radical recombination mechanisms (R02 /R02 ) can cause significant differences in computed [HO ] in regions of low NO and NMHC levels. The effect of cloud chemistry in the troposphere has also recently been studied (151,180). The rapid aqueous-phase breakdown of formaldehyde in the presence of clouds reduces the source of HOj due to RIO. In addition, the dissolution in clouds of a NO reservoir (N2O5) at night reduces the formation of HO and CH2O due to R6-RIO and R13. Predictions for HO and HO2 concentrations with cloud chemistry considered compared to predictions without cloud chemistry are 10-40% lower for HO and 10-45% lower for HO2. 

Keywords satellite - remote sensing - troposphere - stratosphere - trace gas -atmospheric chemistry... 

Aerosol concentrations and size distributions can be investigated remotely using sun-photometry. Characterization of volcanic aerosol is important in smdies of plume chemistry, atmospheric radiation, and the environmental and health impacts of particle emissions. Watson and Oppenheimer (2000, 2001) used a portable sun-photometer to observe tropospheric aerosol emitted by Mt. Etna. They found distinct aerosol optical signatures for the several plumes emitted from Etna s different summit craters, and apparent coagulation of particles as the plume aged. More recently. Porter et al. (2002) have obtained sun-photometer and pulsed lidar data for the plume from Pu u O o vent on Kilauea, Hawaii, from a moving vehicle in order to build profiles of sulfate concentration. 

A64. Vogt, R. Cmtzen, P.J., 1996 Modelling of Halogen Chemistry in the Remote Marine Boundary Layer , in BorreU, P.M. Cvitas, T. Kelly, K. Seiler, W., (Eds.) Proceedings of the EUROTRAC Symposium 96, Garmisch-Partenkirchen, Germany, 25—29 March 1996 on Transport and Transformation of Pollutants in the Troposphere, Vol. 1, Clouds, Aerosols, Modelling and Photo-oxidants (Southampton Computational Mechanics Publications) 445-449. 

The photodecomposition of the various oxidation products of the alkanes, alkenes, and the aromatic hydrocarbons play important roles in the chemistry of the urban, mral, and remote atmospheres. These processes provide radical and other reachve products that help drive the chemistry that leads to ozone generation and other important chemistty in the troposphere. In this chapter, we have reviewed the evidence for the nature of the primary processes that occur in the aldehydes, ketones, alkyl nitrites, nittoalkanes, alkyl nitrates, peroxyacyl nitrates, alkyl peroxides, and some representative, ttopospheric, sunlight-absorbing aromatic compounds. Where sufficient data exist, estimates have been made of the rate of the photolytic processes that occur in these molecules by calculation of the photolysis frequencies ory-values. These rate coefficients allow estimation of the photochemical lifetimes of the various compounds in the atmosphere as well as the rates at which various reactive products are formed through photolysis. 

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