Tropospheric ozone

As summer smog (also smog, ozone smog or LA smog ) is defined as the load on the ground-level air (smog ) by a high concentration of ozone. It occurs in sunny weather and arises from nitrogen oxides and hydrocarbons in conjunction with the UV radiation from the sun. Ground-level ozone attacks the respiratory system and damages plants and animals. The ozone pollution of the environment is determined by air monitoring stations and regularly depicted in charge cards and published.

Formation

Ground level ozone is formed with the participation of nitrogen oxides and is influenced by the solar radiation. Nitrogen is cleaved by UV radiation into nitrogen monoxide and oxygen. This atomic oxygen with an oxygen molecule to form ozone:

NO2 light ( λ < 420 nm) → NO • • • O

• O • O2 → O3

At the same time builds nitric oxide ( NO) ozone to form nitrogen dioxide and oxygen again:

NO O3 → NO2 O2

C, the ozone concentration (O3) is therefore dependent on the nitrogen concentration, the nitrogen concentration and the light intensity:

With K as the equilibrium constant.

The formation of ozone is also favored by hydrocarbons, as these transform under sunlight nitric oxide to nitrogen dioxide:

O3 UV radiation → O2 O • •

• O • H2O → 2HO •

HO • R -CH 3 → R- CH 2 • H2O

R- CH 2 • O2 → R -CH 2 O -O •

R -CH 2 O -O • NO → R -CH 2 O • NO2

R -CH 2 O • O 2 → R -CHO HO -O •

HO -O • NO → NO2 OH •

The OH radical thus acts as a catalyst and is not consumed. In the overall balance gives:

R- CH3 2O2 2NO → RCHO 2NO2 H2O

Ozone creation potential

The example of a vehicle with an internal combustion engine exhaust gases emitted contribute to the different reactivities of its components (VOC ) to ozone formation in the troposphere. In particular, unburned hydrocarbons have a high reactivity with HO- radicals and accordingly a high ozone formation potential.

Ozone is the main component of photochemical smog ( smog ), which is mainly caused by transport, industry and households.

Scale for the assessment of ozone formation potential is an early 90 developed in the U.S. method, the exhaust gas components detected and assessed individually in the context of the statutory driving cycle tests (eg U.S. FTP). In California, this process is now in the certification of new licensed vehicles on the market - especially those with reformulated and alternative fuels - used.

This is done using the MIR scale (maximum incremental reactivity ), which allows the consideration of relative ozone formation potentials under certain atmospheric conditions. MIR factors have now been empirically determined for about 200 exhaust components.

Components with the highest reactivities are some olefins ( ME = 8-11 gO3/gVOC ), some aromatics (7-9 gO3/gVOC ) and some oxygenates (aldehydes with 5-7 gO3/gVOC ); the lowest reactivity with methane has 0,015 gO3/gVOC.

Vehicle tests have demonstrated the following:

  • The ozone formation potential is reduced by a catalyst by 80-95 % compared to a catalyst -free vehicle
  • Very cheap is a natural gas (CNG) powered vehicle
  • Only minor differences arise, however, between other fuels ( gasoline, diesel, alcohol fuels M85/E85 )
  • In petrol mode 50% of the ozone formation potential of only 4 exhaust components are formed, following 40 % against 16 other components
  • In gas (CNG) and diesel mode 50% of the ozone formation potential of only two components are formed
  • Similarly, ( M85/E85 ) in alcohol operation formed by only two components (formaldehyde and acetaldehyde, respectively, unburned alcohol), following 40 % against 18 other components of 50% of the ozone formation potential.

Other sources of ozone

Ozone is also produced by electrostatic discharges in laser printers, photocopiers and fax machines, as well as by lightning.

Effects in humans

The odor threshold of ozone is 40.2 ug / m³, but you get used to the smell quickly and then does not notice it him.

Ozone penetrates as irritant gas deep into the lungs and can cause inflammation. Depending on the duration of exposure and the concentration there are health effects such as:

  • Cough
  • Eye irritation
  • Headache
  • Pulmonary disorders

After recommendations from doctors physical exertion at high ozone levels should be avoided.

Legal limits

After the 3rd EU Directive 2002/3/EC for " limits the protection of health " ( 11 June 2010 replaced by the new Air Quality Directive 2008/50/EC ) applies:

Possible countermeasures

Individually helps (short term) to avoid by seeking a closed room or leaving contaminated areas. A long-term reduction can only be achieved at the collective level. Since the weather is seen as one of the triggers as largely unalterable, the measures aim to reduce summer smog from the reduction of nitrogen oxides and volatile hydrocarbons. Since these are caused by traffic, individual combustion plants and industrial / commercial, help (current) system shutdown and traffic avoidance. In the long term retrofit and / or replacement of equipment and vehicles are required.

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