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Ecology in Tula IS getting worse every year. All kinds of stress and the strain on human in an urban environment - it's all the result of lack of oxygen

It is clear that the characteristics of the air we breathe highly depend on the proportion of oxygen. And the amount of oxygen in the atmosphere - not a constant. If the fraction of oxygen in the taiga can sometimes exceed 21.7%, whereas in the cities of not more than 20.8%, let alone in the room even smaller. A good oxygen in the air is - 20,8-21%.

Typically in the interior can only enter the air from the streets, where in fact there is a low oxygen content! Also, a significant expense in the room of this element is in our breath. In general, migraine headaches, bad sleep, headaches and irritability - these are signs of lack of oxygen.

Today, numerous sources of this vital element, the most widely used special hubs. They can produce up to 45% oxygen

" whereas in the cities of not more than 20.8%, let alone in the room even smaller" - тут что то не понятно с конфигурацией словосочетания of not more.

Я бы соствил совсем по другому предложение "If the fraction of oxygen in the taiga can sometimes exceed 21.7%, whereas in the cities of not more than 20.8%, let alone in the room even smaller." Мне тут смысл не совсем понятен. Напишите русский вариант предложения.