The effects of smog on the environment and human health

The effects caused by a long exposure to low concentrations of ozone are not yet well understood

by Lorenzo Ciotti
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The effects of smog on the environment and human health

The effects caused by a long exposure to low concentrations of ozone are not yet well understood, even if the thesis according to which this would lead to an acceleration in the aging of the lung tissue due to the oxidation of some compounds in the proteins is being confirmed.

Acute effects are more documented than chronic ones. Controlled studies conducted at exposure levels of about 190 µg/m³, report symptoms such as chest discomfort, cough, headache for children and young people. The risk deriving from exposure to ozone depends on the duration of exposure and the concentration present; the greatest effects were found for an exposure time greater than one hour.

Notable disasters due to smog are recorded in Donora Pennsylvania and the Great Smog in London. Pollutants such as ozone, peroxyacetylnitrates, sulfur dioxide and ethene can enter plants through the stomata of leaves where they destroy chlorophyll.

The consequences on plants are deleterious, from the interruption of growth to death. The threshold value, often expressed in AOT40, above which visible leaf damage occurs on sensitive plants, is 700 ppb/hour, calculated over three days.

The threshold value beyond which yield drops occur for the most sensitive crops. is 5300 ppb/hour of ozone determined in the three months of the growing season. The effect of ground-level ozone on lung function and respiratory symptoms has been well documented in acute photochemical pollution situations.
Acid rains are mainly caused by sulfur oxides (SOx) and, to a lesser extent, by nitrogen oxides (NOx).

It has been seen that these gases are typically present in smog, from which they pass directly or indirectly to rain. If they do not come into contact with water droplets, these gases can deposit on the ground with different mechanisms governed by the size of the particles, by impact and gravity, by the state of the air in contact with the receiving surface and by the chemical and physical structure of the surface itself.

In any case, the dry deposits of SOx and NOx quickly lead to the formation of the relative acids in the soil. These topics are detailed in the appropriate item. Smog helps to increase the greenhouse effect, as it contributes to the formation of so-called greenhouse gases, such as carbon dioxide and sulfur dioxide (London smog), nitrogen oxides and others (Los Angeles smog).