What is ozone?
Ozone (O₃), also known as superoxide, is an allotrope of oxygen (O₂). At room temperature, it is a light blue gas with a peculiar odor. Ozone gas is mainly distributed in the stratospheric atmosphere at an altitude of 10-50km, with the extreme values between 20-30km altitude.
At room temperature ozone gas can be self-reduced to oxygen. It has a higher specific gravity than oxygen, is slightly soluble in water, and is easily decomposed. Ozone is carried by an oxygen molecule with an oxygen atom, so it is only a temporary state. In addition to oxidizing the oxygen atoms carried out, the remaining combination of oxygen into a stable state, so ozone has no secondary pollution. The decomposition of ozone in aqueous solution is faster than its decomposition in air. The half-life of ozone decomposition in water is related to temperature and pH.
Sources of ozone gas
Natural factors
In the early days of the Earth, ultraviolet light shining on atmospheric water vapor produced free radicals (e.g., hydrogen atoms and hydroxyl groups). These free radicals continued to react in the atmosphere and were involved in the production of oxygen in the early atmosphere. About 3 billion years ago, blue-green bacteria and early plants began to utilize solar energy for photosynthesis, and the amount of oxygen in the atmosphere gradually increased, which was a prerequisite for ozone production.
When the atmospheric oxygen content reaches a certain level, ultraviolet radiation makes the oxygen molecule (O2) photolysis into two oxygen atoms (O). These oxygen atoms combine with other oxygen molecules in the atmosphere to form ozone (O3). Alternatively, in the presence of lightning, atmospheric water vapor breaks down into hydrogen and oxygen atoms, which then combine with oxygen molecules to form ozone. Ozone absorbs ultraviolet light while releasing oxygen atoms that continue to participate in the synthesis of ozone.
These reactions continue in the atmosphere, reaching a dynamic equilibrium and forming the ozone layer. The ozone layer is found in the Earth’s atmosphere between the stratosphere and the stratosphere, in an altitude range of about 15 to 35 kilometers. Ozone gas at this altitude can amount to more than 90% of the total ozone in the atmosphere. The ozone layer effectively absorbs ultraviolet light and can protect living things from solar radiation. Over time, life arises.
Human factors
The mechanism of ozone formation due to human activities is very complex, but in simple terms: hydrocarbons and nitrogen oxides (NOx) form ozone in the presence of UV light. In many cases, ozone gas shows a snowballing upward trend. Due to the involvement of volatile organic compounds (VOCs), their free radicals create a chain amplification, resulting in a continuous increase and accumulation of ozone gas. When the sun goes down in the west or other influences, the chain reaction is interrupted and the ozone concentration drops.
What are the benefits of ozone?
For the environment
Ozone protects the atmosphere. Ozone gas forms the ozone layer in the Earth’s atmosphere, a layer that effectively absorbs and filters out high-energy ultraviolet (UV) radiation and protects life on Earth from UV damage. In addition, ozone gas is an important oxidizer in the atmosphere. It participates in many chemical reactions, for example, with substances such as nitrous oxide and sulphur dioxide, thereby affecting the redox balance in the atmosphere and regulating the chemical composition of the atmosphere.
For water treatment
Industrial wastewater contains a large number of difficult-to-break down organic substances and dyes, which have a great impact on water bodies and ecological environment. Ozone has a strong oxidizing ability, which can decompose these difficult-to-break down organics and dyes into harmless substances, so as to achieve the purpose of water purification. For example: electroplating plant wastewater treatment, printing and dyeing plant wastewater treatment, chemical plant wastewater treatment and so on. Among them, printing and dyeing wastewater treatment is one of the most widely used fields of ozone. As printing and dyeing wastewater contains a large number of difficult to degrade organic substances and dyes, ozone treatment can effectively decompose these harmful substances into harmless substances, achieving the purpose of protecting the environment.
For medical treatment
Ozone gas is also important in the medical field and has the unique ability to treat a wide range of diseases. Ozone is capable of oxidizing fungi, bacteria and viruses, destroying their cell walls and cell membrane structures, thus achieving sterilization and disinfection. In addition, a reasonable concentration of ozone can activate cell and tissue activity within the body and improve the body’s resistance. It can promote the normal cellular metabolism, accelerate the healing of wounds and improve the immune function of the body.
For food processing
Ozone also plays an important role in the food processing and storage industry. During food processing, ozone can effectively kill bacteria, mold and other microorganisms to prevent food spoilage and contamination. At the same time, ozone gas can also extend the freshness period of food to ensure the safety and hygienic quality of food. In the process of transportation, ozone has strong killing and inhibiting ability for mold, and at the same time, it can absorb the ethylene gas discharged from the respiration of fruits and vegetables, and inhibit the ripening of fruits and vegetables in storage. For food, fruits and vegetables have a better mold, freshness effect.
How can ozone gas levels be measured?
1. Ozone Sensors
Detection is carried out using an ozone sensor. Based on the electrochemical principle, ozone gas concentration is measured by generating a current signal through a chemical reaction between the electrodes on the surface of the sensor and ozone. There are many types of gas sensors for different measurement locations. Common ozone sensors are wall-mounted, duct-mounted and portable.
Wall-mounted ozone sensor
Suitable for monitoring ozone gas in factories, warehouses and other fixed locations.
Duct type ozone sensor
Suitable for monitoring ozone gas in pipelines or confined spaces.
Portable ozone detector
Suitable for professional gas monitors to monitor different places.
2. Ultraviolet light absorption
Measurements are made using the absorption properties of ozone for ultraviolet light. A source of UV light is radiated into a sample of ozone gas, and the difference in intensity between the incident and transmitted light is measured to calculate the ozone concentration.
3. Gas Chromatography
A gas chromatograph is used to separate and measure ozone in a gas sample. Gas chromatography is a more accurate measurement method, but requires specialized instrumentation.
How to choose ozone gas sensor?
When purchasing an ozone gas detector, you must first clarify the characteristics of the use environment and the purpose of use and combine the stability, sensitivity, selectivity, and corrosion resistance of the ozone monitoring equipment to choose.
Stability refers to the stability of the basic response of the sensor during the entire working time, which depends on the zero drift and interval drift. Zero drift refers to the change in sensor output response during the entire working time when there is no ozone. Interval drift refers to the output response change of the sensor continuously placed in ozone, which is manifested as the decrease of the sensor output signal during the working time. Ideally, a sensor under continuous working conditions, the annual zero drift is less than 10%.
Sensitivity refers to the ratio of the ozone gas sensor output change to the measured input change, and it mainly depends on the technology used in the sensor structure. The design principles of most gas sensors use biochemistry, electrochemistry, physics, and optics. The first thing to consider is to select a sensitive technology that has sufficient sensitivity for the detection of the target gas’s valve limit (TLV-threshold limit value) or the lowest explosive limit (LEL-lower explosive limit) percentage.
Selectivity is also called cross-sensitivity. It can be determined by measuring the sensor response produced by a certain concentration of interfering gas. This response is equivalent to the sensor response produced by a certain concentration of ozone gas. This characteristic is very important in the application of tracking multiple gases because the cross-sensitivity will reduce the repeatability and reliability of the measurement. The ideal ozone sensor should have high sensitivity and high selectivity.
Corrosion resistance refers to the ability of the ozone gas sensor to be exposed to a high volume fraction of target gas. When a large number of gas leaks, the probe should be able to withstand 10-20 times the expected gas volume fraction. Under normal working conditions, the sensor drift and zero-point correction value should be as small as possible.
