There is a pppt

1. PHOTOCHEMICAL
SMOG
LOS ANGELES AIR POLLUTION

2. WHAT’S THE MOST COMMON SIGHT
WHEN YOU APPROACH A LARGE CITY BY
AIRPLANE?

3. URBANIZATION AND AIR QUALITY
• Urbanization high concentration of people, industries and
automobiles.
• Exhaust gases from internal combustion engines: CO, CO2, HC
(hydrocarbons), and nitrogen dioxide (NO2).
• NO2 is the precursor of photochemical smog.
• In the presence of sunlight, photochemical reactions occur that produce
smog. (Photochemical reactions are chemical reactions that involve light
photons).
• Local climate can make the problem worse.

4. PHOTOCHEMICAL SMOG – THE STORY OF
LOS ANGELES AIR QUALITY
• Three main ingredients of photochemical smog:
high automobile traffic volume, plenty of sunlight,
and very stable atmosphere (e.g.,Los Angeles
Basin).
• High traffic volume
• Eastern Pacific High –
• Subsidence produces inversion, resulting in an
absolutely stable condition.
• Subsidence also produces clear condition
more sunlight.
• Topography – basin helps trapping pollutants

5. CHEMICAL REACTIONS OF SMOG
A few important reactions:
(1) NO2 + h  NO + O (h represents a photon)
fast (2) O + O2 + M  O3 + M (M represents a neutral molecule)
(3) O3 + NO  NO2 + O2
(4) O + HC (hydrocarbon) stable product + F.R. (free radical)
slow (5) O3 + HC  S.P. + F.R.
(6) F.R. + HC  S.P. + F.R.
(Being a stable product doesn’t mean it is pleasant! It can be irritating to our body.)
(7) F.R. + NO  F.R. + NO2
fast (8) F.R. + NO2  Stable Product (PAN-Type, Peroxyacetyl Nitrate )
(9) F.R. + F.R.  Stable product
• The most important reactions are (1)-(3).

6. DAILY CONCENTRATION VARIATION OF SMOG C

7. PHOTOCHEMICAL SMOG AND WEATHER
• The following slides show the close relationship between the air quali
and meteorological conditions.

9. WE CAN USE THE OZONE LEVEL S A GENERAL AIR QUALITY INDEX. ON
THIS DAY, THE PEAK OZONE LEVEL AT PASADENA WAS NEARLY 200 UNITS
WHILE IT WAS ABOUT 80 UNITS IN WEST LA. HIGH OZONE LEVEL
INDICATES POOR AIR QUALITY.

10. A LOW PRESSURE SYSTEM
WAS MOVING CLOSER TO THE
WEST COAST AND A COLD
FRONT WAS APPROACHING
SOUTHERN CALIFORNIA. THE
WEATHER WAS EXPECTED TO
BECOME CLOUDIER AND THE
AIR LESS STABLE. USUALLY
THE AIR QUALITY CAN BE
EXPECTED TO IMPROVE
UNDER SUCH WEATHER
CONDITION.