Which one of the following is a greenhouse gas and a criteria air pollutant under national ambient air quality standards but is not directly emitted in the troposphere?

Correct option is D

1. Tropospheric Ozone (O3 ​):
· O3​ is a secondary pollutant and a greenhouse gas.
· It is formed in the troposphere by photochemical reactions involving precursors such as nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight.
· Unlike primary pollutants, it is not directly emitted into the atmosphere but forms through chemical processes.
2. Greenhouse Gas Role:
· O3​ contributes to global warming by trapping heat in the atmosphere.
· It is a potent greenhouse gas with a short atmospheric lifetime compared to other gases like CO2​.
3. Criteria Air Pollutant:
· Tropospheric ozone is a key air pollutant regulated under national ambient air quality standards (NAAQS) due to its harmful effects on human health, vegetation, and ecosystems.
4. Other Options:
· N2O: Greenhouse gas, but not a criteria air pollutant.
· CO2​: Greenhouse gas, but not listed as a criteria pollutant under NAAQS.
· SF6: Strong greenhouse gas but not a criteria air pollutant.
Information Booster: 1. Greenhouse Gases:
· Include CO2, CH4​, N2O, H2O, SF6​, and O3​.
· Contribute to the greenhouse effect by trapping heat in the Earth's atmosphere.
2. Criteria Air Pollutants under NAAQS:
· Particulate Matter (PM10​ and PM2.5)
· Nitrogen Dioxide (NO2​)
· Sulfur Dioxide (SO2)
· Carbon Monoxide (CO)
· Ozone (O3​)
· Lead (Pb)
3. Health Effects of Tropospheric Ozone:
· Causes respiratory issues, exacerbates asthma, and reduces lung function.
· Damages crops and natural vegetation.
4. Distinction Between Tropospheric and Stratospheric Ozone:
· Tropospheric ozone: Pollutant and greenhouse gas harmful to health and environment.
· Stratospheric ozone: Protects life by absorbing harmful UV radiation.