Barrons AP Environmental Science

■ Nitrite   (NO 2 – )   is  further reduced to  nitric  oxide   (NO),   molecular   nitrogen

(N 2 ), and nitrous oxide   (N 2 O).

Nitrous  oxide   also    causes  ozone   depletion   whereby     nitrous     oxide   (N 2 O)

gives rise to nitric oxide (NO) on reaction with oxygen atoms: N 2 O + O → 2NO

and NO in turn reacts with ozone: NO + O 3 → NO 2 + O 2 . Nitrous oxide is one

of the most significant ozone-depleting substances and is expected to remain so
throughout the 21st century.

OZONE (O 3 )

Ozone is an inorganic molecule with the chemical formula O 3 . Tropospheric

ozone is a secondary air pollutant. Examples include: (1) UV reacting with the
NOx released by vehicles, which causes oxygen atoms to react with O 2 gas,

resulting in ozone O 3 :

NO 2    +   uv  →   NO  +   O

O   +   O 2     →   O 3

or (2) when volatile organic compounds (VOCs) react with NOx, producing

peroxyacyl nitrates (PANs), which are powerful respiratory and eye irritants that
are present in photochemical smog:

NOx +   VOCs    →   PANs    +   O 3

Human activities that can lead to the formation of tropospheric ozone include
burning fossil fuels (e.g., power plants, motor vehicles, etc.) and releasing
VOCs. Ozone is a short-lived greenhouse gas that decays in the atmosphere
much more quickly than carbon dioxide does. Because of its short-lived nature,
tropospheric ozone does not have strong global effects, but instead is more
influential in its effects on smaller, more localized areas.
Tropospheric ozone can:
■ Harm lung function and irritate the respiratory system
■ Cause asthma and bronchitis
■ Suppress the immune system
■ Result in heart attacks and other cardiopulmonary problems