NOX chemistry

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. 

In addition to the compounds that are directly emitted, there are a number of compounds formed in the plume from the VOC-NOx chemistry described earlier. In particular, the emissions from biomass burning have been observed to form elevated concentrations of 03 over large regions (e.g., Fishman et al., 1986, 1991 Logan and Kirchhoff, 1986 Cros et al., 1992 Andreae et al., 1994 Kim and Newchurch, 1996, 1998 Levy et al., 1997 Mauzerall et al., 1998 Jonquieres et al., 1998 Poppe et al., 1998). 

In short, the overall features of the chemistry involved with the massive destruction of ozone and formation of the ozone hole are now reasonably well understood and include as a key component heterogeneous reactions on the surfaces of polar stratospheric clouds and aerosols. However, there remain a number of questions relating to the details of the chemistry, including the microphysics of dehydration and denitrification, the kinetics and photochemistry of some of the C10x and BrOx species, and the nature of PSCs under various conditions. PSCs and aerosols, and their role in halogen and NOx chemistry, are discussed in more detail in the following section. 

As discussed in detail throughout this book, there is rich and complex chemistry involving volatile organic compounds (VOCs), oxides of nitrogen, and ozone in ambient air. One might therefore anticipate similar chemistry in indoor air environments, and although there are far fewer studies, this does indeed appear to be the case. Weschler and Shields (1997b) and Wolkoff et al. (1997, 1999) review VOC-NOx chemistry that could potentially be important in indoor air enviro-ments and the implications for human exposures. 

The rate constants for all these reactions are reasonably well established, so that the concentrations of OH expected can be predicted with some degree of reliability. (This would not be true if the concentration of organics was high enough to perturb the NOx chemistry because of the many uncertainties in the mechanisms of the organic reactions.)... 

Related to the use of indicator species is the use of species age in photochemical modeling studies (Venkatram et al., 1998). In this approach, the VOC and NOx are calculated at a particular point of interest in an air basin assuming no chemical reactions, i.e., only transport occurs. The age of the VOC and NOx since the time of emission is also calculated. The amount of 03 formed is then estimated using the VOC-NOx chemistry for that time period. This approach separates transport and chemistry in an explicit manner and allows the calculation of the effectiveness of various VOC and NOx reductions at a particular location. 

In 1979, the Department of Energy initiated support of a number of fundamental projects in the chemistry of flue gas desulfurization. Five chapters in this book report the initial results of this effort. The topics of fundamental work include thermodynamic properties, activity coefficients in aqueous solutions, sulfur and NOx chemistry, and sulfite oxidation kinetics. The results provide the foundation for quantitative understanding of the FGD processes. 

Other Biogenic Hydrocarbons 292 Summary of Organic/NOx Chemistry 292... 

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