Troposphere tropospheric chemistry

Crutzen P J 1995 Overview of tropospheric chemistry developments during the past quarter century and a look ahead Faraday Disouss. 100 1-21... 

David T. Allen, Pollution Prevention Engineering Design at Macro-, Meso-, and Microscales John H. Seinfeld, Jean M. Andino, Frank M. Bowman, Mali J. L. Forstner, and Spyros Pandis, Tropospheric Chemistry... 

Atkinson R (1990) Gas-phase troposphere chemistry of organic compounds a review. Atmos Environ 24A 1-41. 

Atkinson, R. (1997) Gas-phase tropospheric chemistry of volatile organic compounds l. Alkanes and alkenes. J. Phys. Chem. Ref. Data 26, 215-289. 

Tropospheric chemistry is strongly dependent on the concentration of the hydroxyl radical (OH), which reacts very quickly with most trace gases in the atmosphere. Owing to its short boundary layer lifetime ( 1 s), atmospheric concentrations of OH are highly variable and respond rapidly to changes in concentrations of sources and sinks. Photolysis of ozone, followed by reaction of the resulting excited state oxygen atom with water vapour, is the primary source of the OH radical in the clean troposphere ... 

Lloyd AC. 1979. Tropospheric chemistry of aldehydes. Washington, DC National Bureau of Standards. Special Publication No. 557. 

Collisional deactivation and energy transfer play important roles in tropospheric chemistry. For example, electronically excited S02 in the 3B, state can be deactivated by 02 (as well as by N2 and H20) to the ground ( A,) state, with part of this process occurring via triplet-triplet energy transfer to generate singlet electronically excited states of 02 ... 

In gas-phase tropospheric chemistry, the most common units for concentration, N, are molecules cm-3 and for path length, /, units of cm. The form of the Beer-Lambert law is then... 

To illustrate the application of Eqs. (OO) and (PP), let us calculate the rate of photolysis of acetaldehyde. Aldehydes such as CH3CHO play an important role in tropospheric chemistry because they photodissociate to produce free radicals. In the case of acetaldehyde, there are four possible sets of products ... 

There are several highly useful sources of data on the absorption spectra and photochemistry of atmospheric species. NASA publishes on a regular basis a summary of kinetics and photochemical data directed to stratospheric chemistry (DeMore et al., 1997). However, much of the data is also relevant to the troposphere. This document can be obtained from the Jet Propulsion Laboratory in Pasadena, California. Alternatively, the data are available through the Internet (see Appendix IV). IUPAC also publishes regularly in The Journal of Physical Chemical Reference Data a summary directed more toward tropospheric chemistry (Atkinson et al., 1997a, 1997b). Finally, Nolle et al. (1999) have made available a CD-ROM containing the UV-visible spectra of species of atmospheric interest. 

As discussed in Chapter 1, nitrous acid is important in tropospheric chemistry because it photolyzes to form OH ... 

For many reactions, the temperature dependence of A is small (e.g., varies with Tl/2) compared to the exponential term so that Eq. (F) is a good approximation, at least over a limited temperature range. For some reactions encountered in tropospheric chemistry, however, this is not the case. For example, for reactions in which the activation energy is small or zero, the temperature dependence of A can become significant. As a result, the Arrhenius expression (F) is not appropriate to describe the temperature dependence, and the form... 

The term fast flow comes from the high flow speeds. In most of these systems, discharges are used to generate A or another species that is a precursor to A hence the term fast-flow discharge system (FFDS) is also commonly applied. Since fast-flow discharge systems have been applied in many kinetic and mechanistic studies relevant to tropospheric chemistry (e.g., see Howard, 1979 Kaufman, 1984), we concentrate on them. However, all fast-flow systems rely on the same experimental and theoretical principles. 

In addition to these highly useful data sets, periodically there are reviews directed to the reactions of one particular species (e.g., OH, N03, or 03) or group of compounds (e.g., R02 radicals). These are referenced in the appropriate sections of Chapter 6. For example, a review of the gas-phase tropospheric chemistry of... 

Alfassi, Z. B S. Padmaja, P. Neta, and R. E. Huie, Rate Constants for Reactions of NO, Radicals with Organic Compounds in Water and Acetonitrile, J. Phys. Chem., 97, 3780-3782 (1993). Allen, H. C., J. M. Laux, R. Vogt, B. J. Finlayson-Pitts, and J. C. Hemminger, Water-Induced Reorganization of Ultrathin Nitrate Films on NaCI—Implications for the Tropospheric Chemistry of Sea Salt Particles, J. Phys. Chem., 100, 6371-6375 (1996). Allen, H. C., D. E. Gragson, and G. L. Richmond, Molecular Structure and Adsorption of Dimethyl Sulfoxide at the Surface of Aqueous Solutions, J. Phys. Chem. B, 103, 660-666 (1999). Anthony, S. E R. T. Tisdale, R. S. Disselkamp, and M. A. Tolbert, FTIR Studies of Low Temperature Sulfuric Acid Aerosols, Geophys. Res. Lett., 22, 1105-1108 (1995). 

Although the photolysis of N02 is the major source of O-, ozone is sufficiently long-lived that it can be transported downwind and survive into the nighttime hours. Hence it is a player in tropospheric chemistry throughout the day and night. 

To pare the list of VOC oxidations down to the most important processes, we can calculate the effective lifetimes of organics with respect to reactions with each of the oxidants listed in the previous section. Since these natural lifetimes are defined as r = 1 / [X], we also need to assume an average concentration for the oxidant, [X]. We can therefore take a typical organic from each of the major classes (alkane, alkene, aromatic, etc.) and compare the individual lifetimes for reaction with OH, 03, N03, etc. Those reactions having very long lifetimes are insignificant with respect to their contribution to tropospheric chemistry and hence can be ignored for the purposes of this discussion. 

The generation of OH in 03-alkene reactions has important implications for tropospheric chemistry. Thus the 03-alkene reactions could be important free radical sources at dusk and during the night when pho-tolytic sources of OH are minimal (e.g., Paulson and Orlando, 1996 Bey et al., 1997 Paulson et al., 1998). For example, Paulson and Orlando (1996) predicted that 10-15% of the total radical production may be from 03 alkene reactions in a typical rural area in the southeastern United States. As seen in Fig. 6.6, this reaction is expected to be most important at night. 

In short, the mechanism of OH-aromatic reactions remains today one of the least understood areas in tropospheric chemistry. 

PAN is known to play an important role in tropospheric chemistry. As discussed in this section, its thermal decomposition releases both N02 and an organic free radical, so that it can act as an NOx reservoir and ultimately as a source of OH in the dark. In addition, PAN is a strong lachrymator (eye irritant), is mutagenic in certain bacterial assays, and is phytotoxic to plants. Because of these broad effects on a variety of systems, its formation and reactions have been studied in some detail. 

Barrie, L and U. Platt, Arctic Tropospheric Chemistry An Overview, Tellus, 49B, 450-454 (1997). 

Crutzen, P. J., Overview of Tropospheric Chemistry Developments during the Past Quarter Century and a Look Ahead, Faraday Discuss., 100, 1-21 (1995). 

Jaffe, D The Relationship between Anthropogenic Nitrogen Oxides and Ozone Trends in the Arctic Troposphere, in The Tropospheric Chemistry of Ozone in the Polar Regions (H. Niki and... 

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