1. Environmental chemistry
E. 10 smog

2. smog
State the source of primary pollutants and the conditions necessary for the formation of photochemical smog.
Outline the formation of secondary pollutants in photochemical smog.

3. smog many different chemicals primary pollutants
secondary pollutants such as nitric acid, aldehydes, organic peroxides and PANs that have been formed from the primary pollutants by free radical reactions brought about by UV from the Sun.

4. photochemical smog: conditions (1)
sunshine: sunlight converts primary pollutants into secondary pollutants; visible sunlight is enough to break bonds in NO2 as there is delocalisation which weakens a bond;
windless day, hot, dry
thermal inversion (cold air below warm air so the air cannot rise)

5. photochemical smog: conditions (2)
relief: city in a valley surrounded by hills
primary air pollutants: nitrogen oxides
and volatile hydrocarbons – VOCs
source: internal combustion engines
time: morning ‘rush hour’

6. formation of secondary pollutants
In the car: N O2  2NO
NO ½ O2  NO2
NO hv  NO O
O O2  O3
H2O O3  O OH
RH O  R OH
Nitric acid:
HO + NO2  HNO3 /OH NO2  HNO3
Hydroxyl free radicals react with VOC to form PANs
PANs : RCO3 + NO2  RCO3NO2

7. smog secondary pollutants primary pollutants nitrogen dioxide ketones,
aldehydes,
PANs,
peroxides,
ozone,
primary
pollutants
volatile hydrocarbons - VOC
nitrogen monoxide

8. photochemical smog (http://www. eco. pref. mie

9. smog: variation in day

10. thermal inversion
Normally, in the troposphere, temperature decreases as you go up; this makes warm and less dense air rise taking pollutants with it. The warmer air is replaced by cooler air which is again warmed up continuing the process;
Thermal inversion occurs when cooler air slips underneath warmer air so that a layer of warm air is trapped between 2 layers of cool air. The bottom cool layer of air, which is denser than the warm layer of air above it, remains close to the surface. Any pollutants released in that layer of cooler air stay close to the Earth’s surface; this allows the primary pollutants to react and produce secondary pollutants and smog.

11. thermal inversion
thermal inversion animation

12. smog: effects
PAN’s cause eyes to water and respiratory problems, also catalyses formation of sulphuric acid,
ozone in the troposphere is:
an eye irritant and also irritates respiratory system
causes deterioration of rubber as it breaks –C=C- and bleaches dyes
affects leaves and therefore growth/damages crops
reduced visibility
secondary pollutants are toxic to plants
corrosion of building materials by acids and ozone.