Smog and the danger to human health

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

by Lorenzo Ciotti
Smog and the danger to 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.

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.
Photochemical smog is also called summer smog or Los Angeles smog because it is more common in hot, dry climates, as typically occurs in the city of Los Angeles (the first cases of photochemical smog were reported around 1940 in Los Angeles).

Chemically, this smog is called oxidizing smog. Photochemical smog is generally important in the summer, when due to the role played by solar radiation in the system of basic chemical reactions, the legal limits for ozone, the main tracer of the process, are more frequently exceeded.

Epidemiological studies have shown that exposure to winter smog is associated with a number of health consequences. Numerous authors have tried to establish a threshold of the average concentration in 24 hours of SO2 and/or particles in suspension, below which there are no significant effects on mortality.

The World Health Organization concluded that the lowest level of pollution found in association with an increase in mortality from exposure to winter smog corresponds to a 24-hour average concentration of 500 µg/m³ of SO2 combined with 500 µg/m³ of black smoke.