Ozone historic concentration

Historically, atmospheric compounds were measured using wet chemical techniques. For example, ozone was measured by bubbling air through a solution containing iodide, and the I2 formed was measured using wet chemical techniques. Such methods were used as early as the mid-1800s to measure ozone in a number of locations worldwide, providing data on the increase in its concentrations since then, discussed in Chapter 14.B.2d. 

The kinetic modeling nomenclature arises from the incorporation of chemical kinetic submodels in EKMA. The empirical term comes from the use of observed 03 peaks in combination with the model-predicted ozone isopleths to develop control strategy options. Thus, the approach historically was to use the model to develop a series of ozone isopleths using conditions specific for that area. The second highest hourly observed 03 concentration and the measured... 

FIGURE 16.26 Effect of assumed boundary and initial conditions on ozone isopleths in the Los Angeles area for reductions in VOC and NOA from August 28, 1987 levels (a) using historical values of measured concentrations (b) clean air values for boundary and initial conditions (adapted from Winner et al., 1995). 

It has been estimated that one chlorine atom has an atmospheric lifetime of one to two years and may destroy 100,000 ozone molecules, thus contributing to the mysterious ozone hole. The British Antarctic Survey discovered the lowest ozone concentration in Earth s atmosphere ever recorded, in October 1984 nearly 40 percent less than the historical average for Antarctica. Atmospheric currents concentrate CFCs over Antarctica, creating the ozone hole that in 1984 was larger than the United States and taller than Mount Everest. The loss of ozone as a protective layer permits the penetration of increased levels of ultraviolet light to Earth s surface. 

There is growing evidence that the composition of the troposphere is changing. For example, analysis of historical ozone records has indicated that tropospheric ozone levels in both hemispheres have increased by a factor of 3-A over the last century. Methane concentrations have effectively doubled over the past 150 years and N2O levels have risen by 15% since pre-industrial times.Measurements of halocarbons have shown that this group of chemically and radiatively important gases to be increasing in concentration until relatively recently. 

Now, back to the two substances that you have been reading about. A lot has happened since the 1970s, when Molina and Rowland hypothesized that CFCs broke down stratospheric ozone. The National Oceanic and Atmospheric Administration (NOAA) and many other groups are actively collecting historic and current data on CFCs in the atmosphere and ozone concentrations in the stratosphere. Through applied research, scientists determined that not only do CFCs react with ozone, but a few other substances react as well. Carbon tetrachloride and methyl chloroform are two additional substances that harm the ozone, as well as substances that contain bromine. 

FIGURE 8 Historical (circles) and recent (triangles) surface ozone concentrations of August/September from different locations in Europe as a function of altitude. The historical measurements from the different sites also Include measurements collected over short periods, whereas the recent data of 1988-1991 are based on continuous monitoring measurements. (For data sources, see Staehelin etai. ( 994). AtmosphericEnviroment 28, 75-87.)... 

Historically most attention has focused on SO2, and its oxidised wet form, sulphuric acid. Overall emissions of SO2 in the Community have declined in the last ten years and this trend may well continue. Without further abatement measures, this decline is not likely to be more than 15% by 2000. Recent investigations in Europe and work in the USA suggest that NOx emissions, which arise from both stationary and vehicle fossil fuel combustion and which are on a rising trend, may also contribute significantly to plant and tree damage. In particular ozone, of which NOx chemical precursor, can, at certain concentrations under summer climate conditions, cause damage or yield effects to some trees and plants, possibly in conjunction with SO2 and NOx ... 

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