<prompt> Translate the following text to EnglishCO2 haijawahi kuamuliwa kama uchafuzi chini ya Sheria ya Hewa safi na haisababishi tishio lolote la moja kwa moja kwa afya ya binadamu tofauti na NOx, SO2 na zebaki.  <response>: However, CO2 has never been regulated as a pollutant under the Clean Air Act and does not pose any direct threat to human health unlike NOx, SO2 and mercury. 