Context

Scientists have evaluated the near-surface ozone in the Brahmaputra River Valley and found a relatively low concentration of ozone over Guwahati compared to the other urban locations in India.

About

What is Ozone?

• Ozone is a colorless gas made up of three oxygen atoms.
• Ozone is not emitted directly into the air but is formed through chemical reactions between natural and man-made emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight.
  
• These gaseous compounds mix like a thin soup in the ambient, or outdoor, air, and when they interact with sunlight, ozone is formed.
• Ozone can be split into two major types:
  • Stratospheric Ozone: Stratospheric ozone or the "ozone layer" forms high in the atmosphere, 6-30 miles above the earth's surface, when intense sunlight causes oxygen molecules (O2) to break up and re-form as ozone molecules (O3).
    • These ozone molecules form the ozone layer and are commonly referred to as "good ozone."
    • At concentrations as high as 12,000 ppb (the EPA considers anything over 70 ppb to be unhealthy for human health and welfare) this ozone protects and shields people, trees, crops, property, and microorganisms from the harmful effects of the sun's ultraviolet light.
  • Ground-Level Ozone: Tropospheric, or ground-level ozone, is created by chemical reactions between:
    • oxides of nitrogen (NOx)
    • volatile organic compounds (VOC)
  • Ground-level ozone forms just above the earth’s surface (up to about 2 miles above ground) and impacts human, animal, and plant respiration. 
  • It usually increases when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources chemically react in the presence of sunlight, impacting human health.

Why ‘Ground-level ozone’ is ‘bad ozone’?

• Although ground-level ozone is less concentrated than stratospheric ozone, its impacts on human health and welfare make ground-level ozone "bad ozone."
• Ground-level ozone is an irritant and can negatively affect human health and welfare. 
• Weather plays a substantial role in formation of ground level ozone. Ground-level ozone concentrations typically are highest on days warm/hot days with low humidity when wind is light or stagnant.

What Scientists have found?

• Scientists analysed the variability of ozone and other air pollutants over Brahmaputra River Valley region.
• It also assessed seasonal, day of week, and characteristics of ozone to identify the emission source of ozone and its precursors, especially methane (CH4) and NMHCs, along with study the relationships between the meteorological parameters, ozone and its precursors in a tropical setting.
• The examination of nitric oxide, nitrogen dioxide, and ozone concentrations in this study suggested that this site is well influenced by local sources such as adjacent major national highway.
• During the daylight hours, the site is in or nearly in a photo-stationary state, indicating a low impact of organic species on the ozone concentrations.