Photochemical Ozone Production or Summer Smog
Ground-level ozone is formed by a combination of sun, nitrogen dioxide (NO2) and volatile organic compound (VOC). Humans in urban areas often release large quantities of organic compounds and at the same time, large amounts of nitrogen oxides (NOX) from combustion, to create electricity and to power cars. In warm temperatures and in sunlight (hence, the name summer smog), these processes generate additional quantities of ozone at ground level.
At ground level (not in the stratosphere), this increase in low levels of natural ozone can harm some plants and may irritate the lining of our lungs. This chemical reaction process of VOCs, NOX, and sunlight is highly complex. The particular chemistry of a VOC, the local concentrations, how high the temperature may be, the wind conditions and other factors are all involved.
The reaction process is "non-linear," meaning that sometimes the NOX concentration will drive the reaction. At other times, it is the VOC that drive the reaction. Various indicators take low, average and high NOX concentrations to calculate an overall score.
A photochemical ozone indicator is derived by finding conversion or reactivity factors for each of the hundreds of possible VOCs. This is then used to convert the many possible inventory VOCs into ethylene equivalents. The interpretation of the photochemical ozone indicator should, however, be done cautiously. As with several other indicators, emissions from different sites are added together.
This results in a total emissions load, and not an understanding of local conditions that actually produce the ozone. Further, general conditions are used rather than local conditions that would typically vary from Stockholm to Barcelona to Munich on a given day.
At ground level (not in the stratosphere), this increase in low levels of natural ozone can harm some plants and may irritate the lining of our lungs. This chemical reaction process of VOCs, NOX, and sunlight is highly complex. The particular chemistry of a VOC, the local concentrations, how high the temperature may be, the wind conditions and other factors are all involved.
The reaction process is "non-linear," meaning that sometimes the NOX concentration will drive the reaction. At other times, it is the VOC that drive the reaction. Various indicators take low, average and high NOX concentrations to calculate an overall score.
A photochemical ozone indicator is derived by finding conversion or reactivity factors for each of the hundreds of possible VOCs. This is then used to convert the many possible inventory VOCs into ethylene equivalents. The interpretation of the photochemical ozone indicator should, however, be done cautiously. As with several other indicators, emissions from different sites are added together.
This results in a total emissions load, and not an understanding of local conditions that actually produce the ozone. Further, general conditions are used rather than local conditions that would typically vary from Stockholm to Barcelona to Munich on a given day.