Tropospheric ozone chemistry

As in the stratosphere the tropospheric ozone is in a dynamic balance between sources and sinks. Ozone can be transported to the troposphere from the stratosphere or can be produced in situ. The main production follows the dissociation of NO2 

Thus the net effect of dissociating nitrogen dioxide is neutral. Net production of tropospheric ozone occurs as a result of other reactions that convert NO into NO2 without destroying ozone. There are many such reactions, most of which involve the photooxidation of chemicals like carbon monoxide, methane and other hydrocarbons. Since these are produced by traffic and industrial processes, ozone production is a feature of polluted regions, and ozone itself is considered a pollutant at low levels of the atmosphere where it is detrimental to human and other life forms. Sinks of ozone include photodissociation and reactions with OH and HO2 (as in the stratosphere) and deposition. 

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The Photochemical Activity and solar Ultraviolet Radiation (PAUR I) and Photochemical Activity and solar Ultraviolet Radiation Modulation Factors (PAUR II) projects had the aim of studying various aspects of ultraviolet radiation and photochemistry interrelationships. PAUR I aimed at studying the interrelationships between total ozone, UV-B radiation, aerosol load, air pollutants, photodissociation rates of N02 and 03 and tropospheric ozone. PAUR II has the aim of studying the interactions between UV-B, total ozone, tropospheric ozone and photochemical activity in the presence of alternating maritime and Saharan aerosols. The present paper presents the main concepts underlying the two projects, the approach followed and a brief overview of some of the results obtained so far. Further, the main results of PAUR I that are relevant to tropospheric ozone chemistry over the Eastern Mediterranean are presented. 

Johnson, J. E. and I. S. A. Isaksen (1993) Tropospheric ozone chemistry the imp)act of cloud chemistry. Journal of Atmospheric Chemistry 16, 99-122 Johnson, M. T. and T. G. Bell (2008) Concept Coupling between DMS emissions and the ocean-atmosphere exchange of ammonia. Environmental Chemistry 5, 259-267 Johnston, H. S. (1971) Reduction of stratospheric ozone by nitrogen catalysts from supersonic transport exhaust. Science 173, 517—522... 

Bauer, S.E., BaUcanski, Y., Schulz, M., Hauglustaine, D.A., Dentener, F. Global modeling of heterogeneous chemistry on mineral aerosol surfaces influence on tropospheric ozone chemistry and comparison to observations. J. Geophys. Res. 109(EX)2304), 17 (2004). doi 10.1029/ 2003JD003 868... 

Understand how photolysis produces radicals by bond cleavage and account for the importance of radical species in photochemical chain reactions, stratospheric ozone chemistry and the photochemistry of the polluted troposphere. 

Triterpenes, structural chemistry, 136 Tropopause, emissions model, 605 Troposphere ozone analysis, 605 trifluoromethyl peroxynitrate, 743 Tryptophan... 

However, tropospheric ozone formed as an air pollutant by VOC-NOx chemistry discussed throughout this book can also impact solar radiation reaching the earth s surface. For example, Frederick et al. (1993) reported that measurements of broadband UV in Chicago had a marginally significant negative correlation to surface 03 concentrations under clear-sky conditions. 

Ehhalt, D., and F. Rohrer, The Impact of Commercial Aircraft on Tropospheric Ozone, in The Chemistry of the Atmosphere, Proceedings of the 7th BOC Priestley Conference., Lewisburg, Pennsylvania, U.S.A. (A. R. Bandy, Ed.), The Royal Society of Chemistry, Cambridge, 1995. 

Oxides of nitrogen play a central role in essentially all facets of atmospheric chemistry. As we have seen, N02 is key to the formation of tropospheric ozone, contributing to acid deposition (some are toxic to humans and plants), and forming other atmospheric oxidants such as the nitrate radical. In addition, in the stratosphere their chemistry and that of halogens interact closely to control the chain length of ozone-destroying reactions. 

The aqueous-phase and gas-phase chemistries of HO, are sufficiently closely coupled that the chemistry shown in Tables 8.11 and 8.12 can affect gas-phase concentrations as well. For example, including the aqueous-phase chemistry in models of tropospheric ozone formation alters predicted 03 concentrations, although whether the perturbation is significant is subject to some controversy (e.g., see Lelieveld and Crutzen, 1990 Jonson and Isaksen, 1993 Walcek et al., 1997 Liang and Jacob, 1997). 

Liang, J., and D. J. Jacob, Effect of Aqueous Phase Cloud Chemistry on Tropospheric Ozone, J. Geophys. Res., 102, 5993-6001 (1997). 

Finlayson-Pitts, B. J., and J. N. Pitts, Jr., Atmospheric Chemistry of Tropospheric Ozone Formation Scientific and Regulatory Implications, J. Air Waste Manage. Assoc., 43, 1091-1100 (1993). 

As discussed in other chapters of this book and summarized in Chapter 16, the formation of tropospheric ozone from photochemical reactions of volatile organic compounds (VOC) and oxides of nitrogen (NC/) involves many reactions. Concentrations are therefore quite variable geographically, temporally, and altitudinally. Additional complications come from the fact that there are episodic injections of stratospheric 03 into the troposphere as well as a number of sinks for its removal. Because 03 decomposes thermally, particularly on surfaces, it is not preserved in ice cores. All of these factors make the development of a global climatology for 03 in a manner similar to that for N20 and CH4, for example, much more difficult. In addition, the complexity of the chemistry leading to O, formation from VOC and NOx is such that model-predicted ozone concentrations can vary from model to model (e.g., see Olson et al., 1997). 

Lelieveld, J., and R. van Dorland, Ozone Chemistry Changes in the Troposphere and Consequent Radiative Forcing of Climate, in NATO AS 1 Series, 132, (1995). 

Similar results have been reported in an intercomparison study of models used to predict tropospheric ozone on a global scale (Olson et al., 1997). Agreement for 03 and NO. was reasonably good for relatively clean atmospheres, with a larger spread for predicted H202. However, introduction of VOC chemistry increased the range of model predictions substantially,... 

In this study we will present aspects of STE in relation with the budget and concentrations of ozone in the troposphere, specifically in the Northern Hemisphere. Firstly, we present ozone observations in the tropopause region from the measurement campaign MOZAIC, and discuss their correlation with potential vorticity. The results have been used to improve the parameterization of stratospheric ozone in a coupled tropospheric chemistry - general circulation model. We will show examples of the performance of the model regarding the simulation of ozone in the tropopause region, and present the simulated seasonality of cross-tropopause ozone transport in relation to other tropospheric ozone sources and sinks. Finally, we will examine and compare the influence of cross-tropopause transports to surface ozone concentrations for simulations with contemporary, pre-industrial, and future emission scenarios. 

We have addressed several aspects of STE of ozone and the impact on tropospheric ozone levels. Using ozone observations in the upper troposphere and lower stratosphere from MOZAIC, we have examined the rdation between ozone and PV in the lower stratosphere. A distinct seasonality in the ratio between ozone and PV is evident, with a maximum in spring and minimum in fall associated with the seasonality of downward transport in the meridional circulation and of the ozone concentrations in the lower stratosphere. The ozone-PV ratio is applied in our tropospheric chemistry-climate model to improve the boundary conditions for ozone above the tropopause, to improve the representativity of simulated ozone distributions near synoptic disturbances and realistically simulate cross-tropopause ozone transports. It is expected that the results will further improve when the model is applied in a finer horizontal and vertical resolution. 

Holton, J.R., and Lelieveld, J. (1996) Stratosphere-troposphere exchange and its role in the budget of tropospheric ozone, in P.J. Crutzen and V. Ramanathan (Eds.), Clouds, Chemistry and Climate, NATO ASI Series, Springer-Verlag, Berlin, pp. 173-190. 

Stevenson D.S., W.J. Collins, C.A. Johnson and RG. Derwent, 1997 The impact of nitrogen oxide emissions on tropospheric ozone studied with a 3-D Lagrangian model including foil diurnal chemistry, Atmos. Env.,31, 1837-1850. 

Several estimates of the radiative forcing due to changes in tropospheric ozone are based on 3D CTMs. The MOGUNT1A model was used by van Dorland et ah (1997), Berntsen et ah (1997) based their work on the Oslo 3D CTM 1 model, and Roelofs et ah (1997) used ozone changes predicted using the European Centre Hamburg Model version 4 coupled to a tropospheric chemistry model. Forster et ah (1996), on the other hand, used two different 2D CTM models to calculate the ozone increase since pre-industrial time, namely the Cambridge and the UK.MO models. One study was based on observations of ozone. Portmann et ah (1997) estimated tropical tropospheric ozone from ozonesonde profiles and ozone columns derived from satellite maps. 

Lelieveld, J. and R. van Dorland, Ozone chemistry changes in the troposphere and consequent radiative forcing of climate, in Atmospheric Ozone as a Climate Gas, edited by W-C. Wang and l.S.A. lsaksen. Springer, Berlin, 1995. 

Yang X, Cox RA, Warwick NJ, Pyle JA, Carver GD, O Connor FM, Savage NH (2005) Tropospheric Bromine Chemistry and Its Impact on Ozone A Model Study. J Geophys Res 110 D23311... 

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