TEHRAN – Heavy pollution in Tehran has persisted during spring and summer due to the rise of ozone gas index (O3), which is mainly caused by motor vehicles’ emitted particles, an official with Air Quality Control Company has said.

Over the past three days, Tehran's air quality index reached a level which is unhealthy for sensitive groups, ISNA quoted Hossein Shahbazi as saying on Tuesday.

By the end of the cold season, air pollution in Tehran was thought to be reduced, but days with unhealthy air pollution increased during spring and summer, he added.

He further noted that air quality of the capital deterioratedduring spring compared to the past two years, due to increase in O3.

In recent years, the concentrations of ozone have not been so high, and air pollution [in summer] has been mostlydue to sand and dust storms, Shahbazi remarked.

Unfortunately, over the past two years, the concentration of ozone has risen through cars emitting particles, he regretted, adding, “air pollution caused by mobile sources affects the capital's air quality in the summer as well”.

Over the past few days “beside high concentrations of ozone near ground level, airborne dust particles were the other factor added to the air pollution,” he explained 

At ground-level, ozone is a pollutant, but in the stratosphere it screens UV radiation. Ozone is one of the conventional (criteria) pollutants, which produce the highest volume of pollutants in the air and the most serious threat for human health and welfare. 

Ozone in the lower atmosphere is formed by the reaction of sunlight on air containing hydrocarbons and nitrogen oxides that react to form ozone directly at the source of the pollution or many kilometers down wind. Cars, industry, gas vapors, chemical solvents, fuel combustion increase ozone production. Half of emission of HC and NOx in cities is by motor vehicles. 

Some of main health effects of ozone are lung inflammation, reduced lung elasticity, transient cough, chest pain, throat irritation and nausea. Other Effects are damages on plants and material like: retard the growth, effect on pollen germination, reduce photosensitize, crack rubber, and react with fabric. 

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