6.5-8.0 ppm \text {6.5-8.0 ppm}6.5-8.0 ppm
3.0-4.0 ppm \text {3.0-4.0 ppm}3.0-4.0 ppm
60.0-95.0 ppm \text {60.0-95.0 ppm}60.0-95.0 ppm
>120 ppm \mathrm { >120 ~ppm}>120 ppm