Environmental chemistry

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.

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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

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formation of secondary pollutants

• In the car N2 O2 ?? 2NO
• NO ½ O2 ?? NO2
• NO2 hv ?? NO O?
• O? O2 ?? O3
• H2O O3 ?? O2 2OH?
• 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

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smog

• secondary pollutants
• nitrogen dioxide
• ketones,
• aldehydes,
• PANs,
• peroxides,
• ozone,

• primary
• pollutants
• volatile hydrocarbons - VOC
• nitrogen monoxide

8
photochemical smog (http//www.eco.pref.mie.jp/en
glish/data-syu/data-sokuhou/img/R06-01_e.gif)
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 Earths
  surface this allows the primary pollutants to
  react and produce secondary pollutants and smog.

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thermal inversion

• thermal inversion animation

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smog effects

• PANs 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 CC-
  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.