According to example configurations herein, a system includes an inertial filter, a temperature controller, and analyzer. The inertial filter has multiple ports including a first port, a second port, and a third port. A sample gas flows between the first port and the third port of the inertial filter. The second port of the inertial filter outputs a portion of the gas flowing between the first port and the second port. The temperature controller controls a temperature of the inertial filter and/or the gas flowing through the inertial filter. The analyzer receives the portion of the gas flow outputted by the second port of the inertial filter and produces a value indicative of a concentration of sulfur trioxide in the portion of the gas flow.