SEN0469 lifetime

I have a question regarding the Gravity NH3 Sensor SEN0469. The lifespan is stated as 2 years, but at what concentration? Electrochemical NH3 sensors usually have a lifespan that depends on the concentration of NH3 they are exposed to. For example, a sensor exposed to 1 ppm will last 10 times longer than a sensor exposed to 10 ppm. The 2-year lifespan is calculated at what concentration?