Ozone

Three oxygen atoms make up ozone (O3), a highly reactive gas. It is a natural and man-made product that exists in the upper (stratosphere) and lower (troposphere) atmospheres of the Earth (the troposphere). Ozone has a positive or negative impact on life on Earth depending on its location in the atmosphere. The interaction of solar ultraviolet (UV) light with molecular oxygen produces stratospheric ozone (O2). The “ozone layer,” which is located about 6 to 30 miles above the Earth’s surface, decreases the quantity of dangerous UV light that reaches the surface. Ozone is a potent oxidant (much more so than dioxygen) with a wide range of industrial and consumer applications.

Photochemical reactions between two primary groups of air pollutants, volatile organic compounds (VOC) and nitrogen oxides, produce tropospheric or ground-level ozone, which we breathe (NOx). Traditionally, these processes have been thought to be dependent on the presence of heat and sunlight, resulting in increased ambient ozone concentrations throughout the summer. However, in the last decade, high ozone concentrations have been observed in specific cold-weather conditions in the Western United States, where a few high-elevation areas with high levels of local VOC and NOx emissions have formed ozone when there is snow on the ground and temperatures are near or below freezing. Ozone contributes to what we often refer to as “smog” or “haze,” which is still prevalent during the summer months.

Although some stratospheric ozone is carried into the troposphere, and some VOC and NOx are produced naturally, the majority of ground-level ozone is produced through VOC and NOx interactions. Chemical plants, fuel pumps, oil-based paints, auto body shops, and print shops are also significant contributors of VOC. High-temperature combustion is the primary source of nitrogen oxides. Power plants, industrial furnaces and boilers, and automobiles are also significant contributors.

Structure:

Ozone is a bent molecule with C2v symmetry, according to experimental evidence from microwave spectroscopy (similar to the water molecule). 127.2 pm are the O – O distances. The angle O – O – O is 116.78°. One lone pair is sp²  hybridized with the central atom. With a dipole moment of 0.53 D, ozone is a polar molecule. The molecule is a resonance hybrid, with two contributing structures, one with a single bond on one side and a double bond on the other. Both sides of the arrangement have an overall bond order of 1.5. It has the same isoelectronic properties as the nitrite anion. Substituted isotopes can be found in naturally occurring ozone (16O, 17O, 18O).

Physical and Magnetic Properties :

• The color of ozone is  pale blue , a gas  that is mildly soluble in water but considerably more soluble  in non-polar inert solvents like carbon tetrachloride or fluorocarbons, where it forms a blue solution. It condenses to create a dark blue liquid at 161 K (112 °C; 170 °F). Allowing this liquid to get to its boiling point is risky because both concentrated gaseous and liquid ozone can explode. It forms a violet-black solid at temperatures below 80 K (193.2 °C; 315.7 °F).

• Most people can perceive 0.01 μmol/mol of ozone in the air, which has a distinct harsh odor similar to chlorine bleach. Headaches, burning eyes, and irritation of the respiratory passages are all symptoms of 0.1 to 1 μmol/mol exposure.

• Even modest levels of ozone in the air are extremely harmful to organic materials like latex, polymers, and animal lung tissue.

• Ozone has a weak diamagnetic property.

Ozone Decomposition:

Ozone is a harmful gas that is widely encountered or produced in human surroundings (aircraft cabins, offices with photocopiers, laser printers, sterilizers, and so on), and its catalytic decomposition is critical for pollution reduction. This is the most common kind of breakdown, especially with solid catalysts, and it has a number of advantages, including better conversion at lower temperatures. Furthermore, the product and catalyst can be separated instantly, allowing the catalyst to be recovered without the need for a separation process. Furthermore, noble metals such as Pt, Rh, or Pd, as well as transition metals such as Mn, Co, Cu, Fe, Ni, or Ag, are the most commonly employed materials in the catalytic breakdown of ozone in the gas phase.

In the gas phase, there are two alternative options for ozone decomposition:

The first is a thermal decomposition, which decomposes ozone only by the action of heat. The issue is that at temperatures below 250 °C, this sort of breakdown is extremely sluggish. However, by working at greater temperatures, the breakdown rate can be increased, albeit at a considerable energy expense.

The second is a photochemical breakdown, which occurs when ozone is exposed to ultraviolet radiation (UV), resulting in the formation of oxygen and radical peroxide.

Is it true that high ambient ozone concentrations can only be found in densely populated areas?

Many people believe that high tropospheric ozone concentrations can only be found in major cities, however high ambient ozone concentrations may and do exist anywhere. Large cities such as Los Angeles, Houston, Atlanta, and New York City are not the only places where ozone is formed. It’s also manufactured in smaller places like Raleigh, North Carolina, and Cincinnati, Ohio, and it’s transported hundreds of miles downwind to impair ambient air quality in other urban and rural areas. Peak quantities of ozone are more common during the afternoon hours, when sunlight is most intense.

Ozone maxima may occur in places downwind of major VOC and NOx sources in the afternoon and evening, after wind has delivered ozone and its VOC and NOx precursors many miles from their origins. As a result, significant ozone concentrations can occur in isolated regions and at different times of day, including early evening and night.

Applications of ozone:

1. Cooling Towers
2. Pharmaceutical ultra pure water
3. Drinking water
4. Odour Control
5. Kitchen off gas treatment.
6. Food and vegetable storage
7. In Swimming pools
8. Greenhouses/Horticulture.

Conclusion:

Ozone is a powerful oxidant (far more powerful than dioxygen) with a wide range of industrial and consumer uses. Ozone’s high oxidising potential causes it to injure mucous and respiratory tissues in animals, as well as tissues in plants, above concentrations of roughly 0.1 ppm. While ozone is a significant respiratory hazard and pollutant near the ground, a higher ozone layer concentration (from two to eight ppm) is advantageous because it prevents damaging UV rays from reaching the Earth’s surface.

Ozone produced by anthropogenic sources in the troposphere, such as automobile emissions, can travel great distances. The daily flux of ozone production and scavenging by other compounds such as NO is constant.