News Excerpt
An analysis by the Centre for Science and Environment (CSE) has revealed upsurge in Ozone pollution amidst nationwide lockdown. It has increased in 22 metropolitan cities and even breached threshold in several cities.

•    Ozone occurs both in the Earth's upper atmosphere in Stratosphere and in the lower layer or the Troposphere.
•    Stratospheric ozone is “good” because it defends living things from UV radiation. Ground-level ozone is “bad” because it can trigger a variety of respirational and health problems.
•    Ozone at ground level is a harmful, secondary air pollutant, and it is the main ingredient in smog. It is highly reactive gas.
•    When emitted pollutants chemically react in the presence of sunlight Ozone is formed in the troposphere.
•    Ozone is most likely to reach unhealthy levels on hot sunny days in urban environments but can still reach high levels during colder months.
•    Ozone can also be transported long distances by wind, so even rural areas can experience high ozone levels.

The Study of CSE
    The analysis was based on Central Pollution Control Board (CPCB) data from 22 cities in 15 States amidst lockdown during March.
    The level of particulate matter (PM) and nitrous oxide levels plummeted during the lockdown, but ozone —a harmful pollutant has increased beyond threshold.
    PM 2.5 levels during the lockdown for all cities were found to be lower than the average for the same period in 2019.
    But when lockdown relaxed, pollution started to increase. The average NO2 levels increased rapidly from the cleanest lockdown phase.
    The pandemic-led change in air quality had helped to understand seasonal & distinct Ozone pollution trends-

Season    Associated factors
It is winter Ozone that draws attention every year.    1. Temperature Inversion
2. Lower mixing height of Air
3. Cold and Calm condition
These all factors trap the air and pollutants near the earth surface.
The summer Ozone pollution is different than winter.     1. High Winds
2. Intermittent Rains
3. High temperature and Heatwave

Possible Reasons
    Ozone is a secondary pollutant that is not directly emitted by any source but is formed by photochemical reactions between oxides of nitrogen (NOx) and other volatile organic compounds (VOCs) and gases in the air under the influence of sunlight and heat. In India, as the lockdown was enforced during the summer months, this effect appears to have compounded, with lower than usual NOx levels at already high temperatures. Ozone is primarily a sunny weather problem in India.
    A high NOx level can again react with ozone and mop it up. The ozone that escapes to cleaner areas has no NOx to further cannibalise it – and as a result, ozone concentration builds up in these areas.
    As nitrogen oxides reduce, photochemical production may become more efficient and can lead to higher ozone concentrations in the summeras higher temperatures increase emissions of biogenic hydrocarbon from natural sources such as trees, significantly affecting urban ozone levels.
    Photochemical production of ozone may become more important in urban areas during summers in the low concentration of oxides of nitrogen.

Impacts of Ground level Ozone
Health Effects:
    Short-term exposure of around an hour is dangerous for those suffering from respiratory problems.
    Breathing ozone can trigger a variety of health problems including chest pain, coughing, throat irritation, and airway inflammation. It also can reduce lung function and harm lung tissue.
    Ozone can worsen bronchitis, emphysema, and asthma, leading to increased medical care.
    In addition, people with certain genetic characteristics, and people with reduced intake of certain nutrients, such as vitamins C and E, are at greater risk from ozone exposure.    

Environmental Effects:
    Ozone affects sensitive vegetation and ecosystems, including forests, parks, wildlife refuges and wilderness areas.  
    It can reduce photosynthesis and slow the plant's growth.
    Rural satellites around cities generally experience high level of Ozone and their agriculture production is known to be adversely affected by high ozone concentrations.

Way forward
    There is a need for an agenda for a ‘blue sky and clear lungs’ for the post-pandemic period to sustain the gains. This action must also ensure the co-benefit of reducing both particulate and gaseous emissions, including ozone.
    Ozone is not emitted directly. It is a secondary pollutant. There is need to control the emission of primary pollutant associated with formation of ozone, that would attribute to the decreasing of ground level Ozone formation.  The ways to minimize the primary pollutant are-
o    Mitigate pollution, NOx vehicular emission by executing BS VI norms.
o    Increase electric mobility and develop electric infrastructure in order to replace emission.
o    Increase public transport and control Industrial pollutant and emission.

SAFAR, Ambient Air Quality

Monitoring of Ozone levels In India-
National Air Quality Monitoring Program (NAMP) is a nationwide program executed by Central Pollution Control Board (CPCB) to monitor the ambient air quality across the country.
    Under NAMP, only four air pollutants namely Sulphur dioxide (SO2), Oxides of Nitrogen, Suspended Particulate Matter (SPM) and RespirableSuspended Particulate Matter (RSPM) are regularly monitored.
    Surface ozone is regularly monitored by the CPCB through automatic monitoring stations.
    The levels are maximum during summer and minimum in monsoon seasons.
    The levels are maximum during daytime and minimum during night or early morning.
    In India, surface ozone levels are above the recommended threshold of 8 hour average of 100 µg/m3.