By the end of the first lockout phase, from March 24 to April 14, the pollutant standard level in Delhi had deteriorated to varying degrees, but the daytime average for the amount of ozone in the air had begun to rise. This was the product of atmospheric chemistry as stated by The Wire study. NOx, the common term essential in atmospheric chemistry for nitrogen oxides, is composed of nitric oxide and nitrogen dioxide. Neither eats ozone, nor does NO2 make ozone.
|| Varsha Sahoo
More than 50 per cent of Delhi’s NOx emissions are caused by car pollution. Ozone accumulates in the atmosphere, with only a limited amount of NO present. The data also shows the same thing that was happening during the ensuring lockdown processes, both in Delhi and across the world. Many datasets demonstrated similar patterns around the globe.
Ozone in the stratosphere is fine; over 10km it blocks ultraviolet radiation from entering the earth from the Sun. Nevertheless, ozone in the troposphere, within 1-2 Km where we live, is not ideal for human health. In addition to 674,000 premature deaths due to PM 2.5 pollution, a global disease burden report concluded that 146,000 people died prematurely from ozone exposure from 1990 to 2017.
Inhaling ozone can cause respiratory difficulties, ranging from shortness of breath to bronchitis and chronic obstructive pulmonary disease, according to the US Environmental Protection Agency. Besides particulate matter-PM 2.5 and PM 10-there are also ozone indoor air quality standards.
Increases in levels of ozone emissions in industrial areas are more prone to the NOx to the VOC ratios. VOC stands for:- organic volatile compounds. And of course, the NOx rates have distinct diurnal periods. The lockdown gave us a chance to check those ideas and learn them better.
There are several gases emitted from sources across the city, each with its own chemical signature. For example, coal burning at an electrical power plant produces more sulfur dioxide in the air around the facility. The engines emit NOx from the burning of gasoline and diesel. VOCs such as benzene spill from bunks of fuel. Garbage set on fire releases dioxins in the air.
When all these gases are released, they combine and react chemically in the atmosphere. We realize there are 500+ potential chemical reactions. They decide how these gasses are produced and breached as they travel across the field, nation and the earth. The ratio of concentrations of NOx and VOC along with meteorology and sunlight plays a central role in determining the ozone presence. Collectively, those reactions are called photochemical reactions.
General data trends suggest that NOx emissions from vehicles in towns help lower ozone levels. In a region, with sufficient concentrations of NOx in the air and sunlight, NO2 breaks down into ozone-forming atoms of NO and ground state oxygen. Then, NO reacts with ozone again to produce NO2. This step, which defines the ozone concentration in the steady-state, is called the photo-stationary state reaction. At the same time, in the presence of hydroxyl radicals, VOCs start the ozone- producing reaction process. An atom with a free valance electron is a radical in chemistry and is charged electrically. The very presence of more NO2 from these reactions will produce more intermediates, which will result in further production of ozone.
We do have carbon monoxide in contaminated conditions and has the ability to contribute to the production of ozone by related reactions with OH- radicals. Coal, biomass, petrol, and diesel combustion all release CO. Both CO and ozone are emitted during hydrocarbon processing. Formaldehyde is a crucial intermediate product: this short-lived gas undergoes photolysis during daytime and produces still more CO.
In cities, the net production of NO2 results in atmospheric chemical reactions and direct pollution. That is why NO2 levels increase at night and ozone levels rise during the day, in accordance with the dominant photo-stationary reaction in the presence of NO. The reactions between NO and ozone becomes slower when we travel higher up the atmosphere, above the city’s boundary layer and away from the main NOx manufacturing fields. As a result, we observe net ozone production and long-range transport.
While urban emissions have less effect on the production of ozone within cities themselves, they make a substantial contribution to the quantity of ozone in non-urban areas. As VOCs and CO race to react with OH- and other intermediate radicals, the NO-ozone reactions delay down. During the lockdowns, the difference between urban and rural areas vanished in the results, in the absence of nearly 70 per cent of the overall NOx pollution, largely due to off-road vehicles. The ratio of NO to NO2 in the automobile emission is usually 19:1.
The overall production of ozone went up during the lockdowns, with little NO in the system to help the photo-stationary reactions which kill ozone molecules. We live in a dynamic, multi-source world, multiple toxins and multiple teams. But to combat air pollution, we need a multi-pronged solution. The research is straightway with certain toxins.
Of starters, if the roads are maintained properly and the contractors meet all construction codes, less dust resuspension will occur and the rates of PM 2.5 and PM 10 will decrease. Unless the government exclusively enforces desulphurization techniques for flue gas, the levels of sulfur dioxide will decrease. However, ozone control needs a more complex approach, because we need to get right the fall in NOx and VOC emissions.