Anthropogenic perturbations

The chemistry of tropospheric ozone production is one of the most extensively studied phenomena of environmental chemistry. However, even this subject has its controversial aspects, particularly with regard to how best to meet US Environmental Protection Agency mandated air quality standards for O3 and NO2. The essential reactions have already been presented in Section 12.4 and will only be discussed briefly here. 

In all high-temperature combustion processes, particularly power plants and automobiles, NO. is produced by the direct reaction of N2 + O2, and from nitrogen-containing fuels. It can then be oxidized by either HO2, RO2, or O3 to NO2. In the presence of NO , and sunlight, the oxidation of CO, CH4, and other hydrocarbons results in substantial ozone production. In an urban environment, the diurnal cycle of these trace species will generally exhibit a characteristic pattern of concentration maxima first in NO, then NO2, followed by O3 around midday (National Academy of Sciences, 1977). This pattern 

As seen in Table 12-4, global NO production is probably dominated by anthropogenic sources in an urban environment, virtually all NOj. is of anthropogenic origin. 

Estimates for the ratio of anthropogenic/natural N2O production range from 0.19-5.50. As mentioned previously, total ozone reductions in the stratosphere have been calculated to be 4% at the present rate of increase of tropospheric N2O (National Research Council, 1984), and could be much larger if N2O concentrations grow at a faster rate. This loss is not balanced by ozone production 

The question of impacts that might arise from 

---

Schaule, B. K., and C. C. Patterson (1981), "Lead Concentrations in the Northeast Pacific Evidence for Global Anthropogenic Perturbations", Earth Planet. Sci. Lett. 54, 97. 

ANTHROPOGENIC PERTURBATIONS OF THE MARINE NITROGEN AND PHOSPHORUS CYCLES... 

In short, although the history of anthropogenic perturbations to the stratosphere is much shorter, it is clear that these are also important. Indeed, such perturbations are expected to affect the chemistry of the troposphere as well for example, increased UV radiation will alter photochemistry at the earth s surface. 

In summary, the chemistry of the stratosphere and the effects of anthropogenic perturbations on it have a rich history, with new chemistry that continues to unfold. For reviews of various aspects of the chemistry and history, see Cicerone (1981, 1987), Rowland (1989, 1992,1993), Molina (1991), Rowland and Molina (1994), Toohey (1995), Brasseur et al. (1995), chapters by Li et al. (1995a), Anderson, and Sander et al. in the book edited by Barker (1995), chapters by Brune, Middle-brook and Tolbert, Wilson, and Brasseur et al. in the book edited by Macalady (1998), and the World Meteorological Organization (WMO) 1995 and 1999 reports Scientific Assessment of Ozone Depletion. ... 

Detecting and quantifying ozone trends in midlatitudes from anthropogenic perturbations is complex due to the effects of natural variations in stratospheric ozone and to the interactions between various effects (e.g., Krzyscin, 1994 Brasseur et al., 1995 Callis et al., 1997 Zerefos et al., 1997 Hood, 1997 Callis et al.,... 

The indirect effect of aerosols on climate, which at present contributes a major uncertainty in understanding anthropogenic perturbations on climate, is a very active area of research. For some typical model treatments of this indirect effect and how it interacts with those due to other, simultaneous, perturbations, see, for example, Jones et al. (1994), Hansen et al. (1997a—d), C. C. Chuang et al. (1997), Lohmann and Feichter (1997), and Pan et al. (1998). 

In short, while net radiative forcing is a convenient means for examining the potential importance of various anthropogenic perturbations for climate, it cannot be used in an additive manner for gases and aerosol particles to predict the ultimate impacts. 

In short, ice core and other long-term records show that there have been dramatic climate changes in the past, some of them within or shorter than a typical human life span. Separating out such natural variability from anthropogenic perturbations remains a major challenge, particularly when it is possible that the anthropogenic emissions may act to hasten or jolt the climate system into a relatively rapid transition from one state to another. 

There are a variety of other climate changes that might be expected to occur simultaneously with changes in temperature. These include changes in precipitation, an increase in the mean sea level, and more variability in the climate. As discussed in detail in IPCC (1996), changes in precipitation patterns and cloudiness have been noted over the past approximately four decades and there is evidence that the sea level has risen by 10-25 cm. The IPCC document should be consulted for detailed evidence for these effects and their possible relationship to anthropogenic perturbations. 

Schaule, B.K. and Patterson, C.C. (1981) Lead concentrations in the Northeast Pacific evidence for global anthropogenic perturbations. Earth. Planet. Sri. Letts, 54, 97-116. 

Over the past few decades the Black Sea has been seriously perturbed by climatic change and intensive anthropogenic contamination. Some nutrients have increased (e.g., NO3 due to eutrophication) while others have decreased (e.g., Si due to Danube river dams construction) [22]. Organisms imported as part of international shipping (e.g., Mnemiopsis and Beroe) have contributed to modification of the natural ecosystem. Understanding the natural temporal variability of the hydrochemistry of the Black Sea is important when trying to determine the effects of these anthropogenic perturbations. 

On a global scale, natural emissions of reduced sulfur compounds account for about 50% of the total sulfur flux into the atmosphere (1-3). Hence, it is important to understand the natural sulfur cycle in order to establish a "base line" for assessing the significance of anthropogenic perturbations (primarily SO2 emissions). Dimethylsul-fide (DMS) is the predominant reduced sulfur compound entering the atmosphere from the oceans (4-9), and DMS oxidation represents a major global source of S(VI). The atmospheric oxidation of DMS can be initiated by reaction with either OH or NO3. In marine environments, however, NO3 levels are typically very low and DMS is destroyed primarily by OH ... 

The anthropogenic perturbations to the stratosphere include inputs of NOx from nuclear weapons testing, high flying aircraft, and of Cl from the photolysis of chlorofluorocarbons, discussed in detail in a later article, but represented by... 

Miller C., Steed J.M., Filkin D.L. and Jesson J.P., The fluorocarbon-ozone theory. VII. One-dimensional modeling — an assessment of anthropogenic perturbations. Atmos. Environ., 15, 729-742 (1981). 

The renewal time is about one year for a mixed layer 100 m deep This indicates that the surface ocean anthropogenic increase should lag that in the atmosphere, but not by much because the anthropogenic perturbation is a decadal to centuries-long process. 

---