Tropospheric

Presented to: Prof. Umesh Kulshrestha

Presented by: Chandrashekhar Azad V.

Ozone

• Ozone (O3), or trioxygen, is a triatomicmolecule, consisting of three oxygen atoms.

• It is an allotrope of oxygen that is much less stable than the diatomic allotrope(O2).

• Ozone is a gas that occurs both in the Earth's upper atmosphere and at ground level.

• Ozone can be "good" or "bad" for people's health and for the environment, depending on its location in the atmosphere.

Ozone

TROPOSPHERIC

• “Bad” ozone is found

• Act as pollutant

• Measured in ppb, µg/m3

OZONE

STRATOSPHERIC

“Good” ozone is found

Act as protective laver

Measure in DU (Dobson unit)

Tropospheric ozone

• In the troposphere, the air closest to the Earth's surface, ground-level or "bad" ozone is a pollutant that is a significant health risk, especially for children with asthma.

• It also damages crops, trees and other vegetation.

• It is the main ingredient of urban smog.

Chemistry

Chemistry

Ground-level or “bad” ozone is not emitted directly into the air,but is created by chemical reactions between oxides of nitrogen(NOx) and volatile organic compounds (VOC) in the presence ofsunlight.

Ozone is made in the troposphere by the same reactionresponsible for its formation in the stratosphere. However, thesource of O is different than in the stratosphere where the Oatoms are made by photo dissociation of O2 at UV wavelength<240 nm. But in the troposphere only UV radiation with >290 nm

is available which can yield oxygen from NO2.

Sources

• The sources of tropospheric ozone are:– Influx from stratosphere– Generation by photochemical reaction in troposphere

• As mentioned earlier VOC and NOx are the main precursors of ozone in the troposphere. These pollutants are emitted from industrial facilities and electrical utilities, motor vehicle exhaust, gasoline vapors and chemical solvents.

Impact of tropospheric ozone• A strong oxidant, tropospheric ozone is harmful to

humans and ecosystems.• Breathing ozone can trigger a variety of health

problems including chest pain, coughing, throat irritation, and congestion.It can worsen bronchitis, emphysema, and asthma. “Bad” ozone also can reduce lung function and inflame the linings of the lungs.

• Ground level ozone leads to damage ofagricultural fields, commercial forest yields,reduced growth and survivability of tree seedlings and also damage of the foliage oftrees and other plants.

• Tropospheric ozone absorbs infrared rays emanating from the earth and works as a powerful green house gas.

• Ozone has its strongest green house effect in upper troposphere.

It is a known cause of photochemical smog, which disturbs human respiratory functions and plant photosynthesis.Due to its green house effect and toxicity, tropospheric ozone is

known as “bad ozone”

Formation of Smog

Formation of Smog

Smog is composed of many different compounds but the main composition of smog is ozone, PAN and volatile organic compounds (VOC).

PAN (peroxy acetyl nitrate) is the product of VOC’s oxygen and nitrogen oxide.

VOCs are uncombusted fuels, often the product of engines.

Air quality index (AQI) for ozone• The AQI is an index for reporting daily air quality. It tells

you how clean or unhealthy your air is, and what associated health effects might be a concern.

Cont… AQI Ozone

concentration (ppb)

0-50 0-59

51-100 60-75

101-150 76-95

151-200 96-115

201-300 116-374

>300 >374

Source: EPA

Note: An AQI of 100 for ozone corresponds to an ozone level of 75 parts perbillion (averaged over 8 hours).

NationalAmbientAirQualityStandards (NAAQS)

PollutantTimeweighted average

Concentration in ambient air

Industrial,residential, rural and other areas

Ecologically sensitivearea (notified by central govt.)

Ozone (µg/m3)

8 hours 100 100

1 hour 180 180

Conclusion

• Ozone in the lower troposphere is considered to be a secondary pollutant and is called ‘bad ozone’.

• Any concentration of O3 240µg/m3 and above is considered to be unhealthy for animals and human beings. 1 hour exposure is sufficient to lead to illness.

• Plants have an injury threshold value of 59µg/m3 of O3 exposure for 4 hours.

• Older leaves are most sensitive to O3 pollution • Both NOx and VOC emission which lead to ozone formation have

been increasing in Asia over the past quarter century. Such a scenario leads to the elevation of tropospheric ozone concentration with serious consequences.

• Urgent action is needed to reduce emissions through international cooperation in the Asian region.

References

• Manahan E. Stanley (2005); Environmental Chemistry• Roy Sovan (2003); Environmental Science, A Comprehensive

Treatise on Ecology and Environment• EPA; AQI, a guide to air quality and your health• Ashmore M.R; Assessing the future global impacts of ozone on

vegetation• Acid deposition and oxidation research center Tropospheric Ozone

A Growing Threat• Upadhyay S. N.; ozone the protective shield of life• Madronich, S. 1993. Tropospheric photochemistry and its response

to UV changes.• http://www.airnow.gov /index .cfm• www.ucar.edu/learn/1_7_1.htm • http://www.epa.gov/oaqps001/gooduphigh/bad.html#6

Thank you