EPA Method 548

The lower limit of detection of SO2 in 10 mL of TCM is 0.75 µg (based on collaborative test results).(7) This represents a concentration of 25 µg SO2/m 3 (0.01 ppm) in an air sample of 30 standard liters (short-term sampling) and a concentration of 13 µg SO2/m 3 (0.005 ppm) in an air sample of 288 standard liters (long-term sampling). Concentrations less than 25 µg SO2/m 3 can be measured by sampling larger volumes of ambient air; however, the collection efficiency falls off rapidly at low concentrations.

Beer's law is adhered to up to 34 µg of SO2 in 25 mL of final solution. This upper limit of the analysis range represents a concentration of 1,130 µg SO2/m 3 (0.43 ppm) in an air sample of 30 standard liters and a concentration of 590 µg SO2/m 3 (0.23 ppm) in an air sample of 288 standard liters. Higher concentrations can be measured by collecting a smaller volume of air, by increasing the volume of absorbing solution, or by diluting a suitable portion of the collected sample with absorbing solution prior to analysis.