Earth’s atmosphere is instilled with multiple things that approves sustenance, as well as has acted as an effective shield against various menacing space phenomenon. One of these priceless shields is the sheath of Ozone Layer Earth is encapsulated within. Ozone exists in the Earth’s stratosphere (also scarcely in Troposphere) from 15 to 35 kilometres above the crust and absorbs 97-99 percent of Sun’s medium-wavelength ultraviolet light, which is a potential hazard to the living cells exposed to it on the Earth’s crust.

Ozone: Characteristics and Distribution

Ozone’s altitude is veritably ideal keeping in mind its characteristics; it acts as a necessary blanket 10 kilometres from the surface of the earth, but is a perilous pollutant at ground level. The high concentrations of Ozone on ground level has its own term; ozone pollution.

Ozone Pollution is an issue of paramount danger in some sectors of the world. Children are more susceptible to experiencing the acute consequences because they stay outdoors more and involve in strenuous activities. You can find out more about the health risks here:

Health Effects of Ozone Pollution | US EPA

Ultraviolet Radiation: Introducing its categories

There are approximately 10 parts per million of ozone in the ozone layer, but it serves its purpose adequately. The following are the types of UV rays and their applications:

UV-A light: Wavelength ranges from 315-400 nm. It’s considered to be the least harmful of the three categories, and has numerous robust industrial applications, the most prominent ones include its use in the painting and manufacturing industries, and in tanning beds (indicating its effect on human skin should it be used cautiously).

UV-B light: Wavelength ranges from 290-320 nm. This type of UV light does more harm than UV-A light, causing skin irritation, burns and amplify the risk of skin-associated cancers. It has multiple industrial applications as well, such as its crucial employment in Phototherapy (alternatively known as Light Therapy, treatment of Cancer using light) as well as in Animal tanks where UV-B light assists the animals in effective synthesis and absorption of Vitamin D3 and Calcium.

UV-C light: Wavelength ranges from 100-280 nm. Owing to its minuscule wavelength, it accommodates enormous amounts of energy which when exposed to skin leads to more detrimental influence than constructive. It scrambles the DNA if exposed to living cells and hence, might lead to Skin Cancer. Its principal Industrial application includes its use in sterilizing hospital rooms, laboratories and operating equipment.

Ozone’s protective functioning

UV-C light can pose extremely hazardous consequences if its exposure exceeds a certain threshold. It might lead to Cataract and other eye disorders, Skin Cancers and Immune system deterioration. However, it is rendered inefficient through the mixture of Oxygen and Ozone, which screen it out at about 35 kilometres from the ground level. Damaging effects notwithstanding, UV-B light is the primary source of Vitamin D for all the flora and fauna. Ozone is transparent to large wavelengths of UV-B light and almost entirely to UV-A light. However, prevalent exposure to these relatively safe categories of UV might still lead to pernicious effects such as accelerated Melanin production, premature-aging and in adverse circumstances, skin cancer.

Tropospheric Ozone: Introduction

Also known as Ground-level ozone, Tropospheric Ozone is the undesirable increase of Ozone in the troposphere, a layer of the atmosphere that exists from ground-level to approximately 14 kilometres above sea level. In the Stratosphere, ozone is extremely substantial, owing to its protective feature. However, as described earlier, ozone close to the ground causes a significant trouble, including instilling chronic breathing issues, deflation of crop outcome, impeding the growth of plants and hence accelerated aging.

This category of ozone roughly constitutes about 10% of the total amount of ozone contained in an air column. This relatively minute quantity of ozone might not seem like a hazard at first glance; however, it is a primary constituent of photochemical air pollution, as well as is responsible for the greenhouse effect. These qualities make tropospheric ozone a life-threatening menace to both, humans and the ecosystem.

Formation of Tropospheric Ozone

The lifespan of Tropospheric ozone is quite small with an atmospheric lifespan of hours to weeks. Its formation is mainly triggered due to the action of sunlight (specifically the UV spectrum) over nitrogen oxides (NO), carbon monoxide (CO), and volatile organic compounds (VOCs) and as a repercussion, the three aforementioned chemical compounds are considered ozone precursors. Although the ozone precursors often originate in urban areas, winds can carry NOx to large distances which by extension, brings semi-urban and remote areas under the influence of tropospheric pollution as well.

Precursor pollutants are largely emitted by anthropogenic activities such as combustion of fossil fuels, operation of automobiles, oil refineries, agricultural activities and a number of other industrial sections. VOCs are generally contributed more by natural vegetation, and up to a minimal extent by human ventures, such as terpenes (found majorly in essential oils) and pinenes (constituent of artificial odorants).

The reaction appertaining the conversion of ozone precursors into ozone occurs using free-radicals. Note that the following reaction also takes place for VOC as well in a similar manner:

CO + 2O2 -> CO2 + O3

The complete detail of the reaction can be found here: Chemistry in the Sunlight (nasa.gov)

Tropospheric Ozone: Impacts

Tropospheric Ozone produces greenhouse effect. Moreover, it is also known of interposing with the natural precipitation rate, evaporation rate and atmospheric circulation and regulation of air and temperature respectively. Quite apparently, it does more damage than just warming up the climate. The amount of affliction of Ozone depends on the quantity of precursors emitted by a certain subcontinental region.

Tropospheric Ozone is also a major constituent of Smog, which holds the capacity to inflict irrevocable damage to the lung tissues, worsen asthmas, bronchitis and emphysema. Children, elderly, and the people with cardiovascular ailments are more susceptible to facing the adverse effects. According to the scientists at the scientists at the University of York Stockholm Environment Institute (SEI), long term exposure to ozone air pollution causes an aggregate of 1 million premature deaths every year.

Tropospheric Ozone also impedes with the natural progression of photosynthesis which retards plant growth and hence, proves to be detrimental where there is extensive crop population.

Preventive Measures

Strategies to reduce ozone pollution is directly associated with reducing methane production (because primary precursors of tropospheric ozone includes hydrocarbons). Some of the effective methods include:

Reduction of leakage from long distance gas transmission and distribution pipelines, recovering and using gas and fugitive emissions during oil and natural gas production.

Upgrading waste management techniques, incentivising anaerobic digestion of solid and liquid waste by food industry.

Improving manure management and animal feed quality, promoting farm-scale anaerobic digestion to control methane emissions from livestock.

Tropospheric Pollution and India

Ozone preferably should exist as a trace gas in the troposphere, with an average concentration of 20-30 parts per billion by volume (ppbv). This magnitude is increased significantly to 100 ppbv in regions where the air is severely contaminated.

Since India is in its phase of rigorous development, its gross domestic product relies fundamentally on agricultural yield. According to the Times of India, Ozone pollution has been found to have damaged 6 million metric tonnes of the country’s wheat, rice, soybean and cotton crops in 2005 (source: Ozone pollution in India damages six million metric tons crops in 2005 | India News - Times of India (indiatimes.com)). This is of utmost concern and measures are being taken to reduce air pollution by the government.

Measurement of Ozone (Tropospheric)

The measurement of Ozone can be done through remote sensing, UV sensors, TOMS (explained briefly in the next section).

TES (Tropospheric Emission Spectrometer) is an instrument equipped in NASA’s Aura satellite in order to study atmospheric chemistry in more detail.

TRopospheric Ozone and its Precursors from Earth System Surrounding (TROPESS) is a NASA funded activity which also aims at studying atmospheric composition and climate change.

Measurement of Ozone (Stratospheric)

Scientists measure Ozone using various instruments. Some such instruments are described as follows:

Ozonesonde: Ozonesonde is a balloon-structured instrument used to monitor the concentration of ozone on various altitudes and transmits the data via radio. This device sucks in and holds the stratospheric air in a chamber (Electrochemical Concentration Cell or ECC) containing Potassium Iodide which reacts with ozone and produces an electrical current.

UV Detectors measure the amount of UV light received on ground level, which by extension gives an estimation of how much ozone is present in the atmosphere.

TOMS or Total Ozone Mapping Spectrometer is a device calculates the amount of Ozone by observing backscattered UV light, that is the UV light emitted from earth back to space. These are generally equipped in Satellites mainly meant for the same purpose. One instance of this technology is the Ozone Monitoring Instrument (OMI) equipped in NASA’s Aura satellite.

Ozone is measured in Dobson Units. According to NASA, one Dobson Unit indicates 0.01 millimetre thickness of ozone gas in an air column.

IIT Kharagpur Unveiled the Increasing Ozone Pollution In Antarctica: A Snippet from Prof. Jayanarayanan and Team

IIT Kharagpur, under the meticulous supervision by Professor Jayanarayanan Kuttippurath, managed to unveil the increasing ozone pollution in Antarctica. This feat was a collaborative research venture with scientists from across the globe: Germany, Italy, Argentina and USA. IIT Tech Ambit reached out to Professor Jayanarayanan, in regard of the accomplishment, and asked a few questions to which he magnanimously responded. This research work relied on Ozonesonde measurements at the Indian Station Maitri in Antarctica.

However, in order to establish veracity and minimize error margins, measurements were also taken from other stations from across the Antarctica; “We had to use measurements from other stations in Antarctica to have continuous long-term measurements, and also to cover the Antarctic Continent to make robust analysis and solid scientific statements on the topic”, Prof. Jayanaranan told us. Sir also commended the application and usefulness of our Indian Measurements, and how this research achievement demonstrates its utility for policy relevant studies.

There are nine contributing authors to this study: Professor Jayanarayanan Kuttippurath, Peter von der Gathen, Irina Petropavlovskikh, Bryan Johnson, Audra McClure-Begley, Paolo Cristofanelli, Paolo Bonasoni, Maria Elena Barlasina and Ricardo Sánchez, along with Pankaj Kumar, Prof. Jayanarayanan’s PhD student, who is the lead author of this study.

Since measuring ground level ozone requires an elaborate apparatus arrangement, the process might have been cumbersome. Instead, the team used balloon-borne instruments here. “The sensor is flown with a balloon, called sonde, balloon sonde, ozone sonde, etc. which are mostly Electrochemical Cell Concentration (ECC) sondes”, said Prof. Jayanarayanan, on being questioned about the equipment employed, instead of the aforementioned non-feasible one.

We asked if the methods that are operated to measure the atmospheric ozone (such as TOMS, UV detectors), Professor responded by saying that these methods are generally not used to measure tropospheric ozone, since they are designed to retrieve total column ozone. Hence, ozone sondes are the optimal method of calculation of tropospheric ozone, since these sondes can measure ozone from the surface to about 30-35 kms. "Most of the instruements, both satellite based (such as TOMS) and ground-based (such as Brewer and Dobson spectrophotometers), are geared towards making observations of stratospheric ozone mainly", said Pankaj Kumar Sir on the same account. On being asked about the potential error margins that come with using ozone measurement techniques, Prof. Jayanarayanan said that most measurements either from satellite or ground-based are subjected to an accuracy of 5-10%, depending on the instrument, season and place (latitudes and altitude variation). In Antarctica, there is snow which leads to a high amount of albedo, and this might affect the accuracy of photo sensitive instruments.

PSCs (Polar Stratospheric clouds, primarily responsible for causing ozone depletion over Antarctica) have negligible contribution to the tropospheric ozone, since these clouds reside in the stratospheric altitudes. Moreover, these clouds appear only in winter/spring; being constrained to seasons, they don’t have substantial contribution to the tropospheric ozone. Prof. Jayanarayanan’s opinions on the same were contemplable, that indirectly, should there be a connection possible in between PSCs which are witnessed in spring, to the hypothesized stratospheric-tropospheric exchange during the same period, then a valid argument of a link between PSCs and tropospheric ozone might be established in some years, when the PSC occurrence is widespread and strong.

Owing to Antarctica’s inhabitable weather conditions, anthropogenic activities do not occur in significant number; the ozone precursors are mostly transported from the adjacent continental regions. “This suggests that there is significant ozone pollution in nearby regions to even contaminate the atmosphere of pristine remote areas such as Antarctica. This is something we need to worry about”, said Prof. Jayanarayanan, expressing his concern over the increasing tropospheric ozone even in a region completely devoid of industries and human settlements.

The article (Ozone pollution has increased in Antarctica - American Chemical Society (acs.org)) mentioned the increased concentration to be around 0.14 ppb. This, however, might not look like a formidable number; but here Prof. Jayanarayanan has asked us to think about its long-term implications, meaning that the adjacent regions are immensely polluted, which is the fundamental concern here. Moreover, Sir also stated that the extent of pollution pivots not only on the concentrations of the unfriendly gases in the atmosphere, but also the health consequences it poses. In the same regard, Pankaj Sir stated that there
are concerns related to the climate change perspective as ozone is a highly potent greenhouse gas with extremely high warming potential.

The pandemic witnessed sedentation by almost the entire world, including the industrial sector. Since the industries are the primary source of ozone precursors, this should have caused a decrease in the magnitude received by research; to this Prof. Jayanarayanan answered by elaborating how there wasn’t a statistically significant decrease in the numbers provided by the feedback; the transportation of pollutants still continued. Moreover, during the lockdown period, the air quality enhanced and during the unlock period, there was air deterioration, but not as contaminated as the time preceding pandemic, “From the existing pollution, some amount reduced. This doesn’t mean the pollution was entirely eradicated”, Professor said. Sir also said that the pandemic gave us an opportunity to adapt this amalgamated lifestyle of going out and staying in in accurate proportions.

On being questioned about any way of reducing the atmospheric pollution in remote locations caused due to the transportation of precursors from adjacent regions, Prof. Jayanarayanan said that the sole solution to this issue will be to control the pollution at the source level. For instance, if the ozone contamination in Antarctica is to be reduced, we should consider looking at the adjacent continental regions and interrupt the emissions of precursors at the source level.

We asked which instrument (Ozone sonde and TES equipped by NASA’s Aura Satellite) is more effective, to which Professor responded that both of the instruments are ideal for different situations, and their juxtaposition does not lead anywhere. “Our research objective was to look at tropospheric and surface ozone concentrations. Hence, the advantage of ozone sonde here is that you can look at pollutant concentration within an interval of few metres, as opposed to satellites where intervals extend to 1 km”, said Professor. Sondes provide accurate measurements when vertical columns are concerned; satellites however, are preferred where measurements are to be ascertained within a region under a certain diameter.

IIT Tech Ambit wholeheartedly thanks Prof. Jayanarayanan and team to bring such an issue of such paramount importance under knowledge, and wishes them all the best for their future endeavours!