A method for calibrating a photoacoustic sensor system comprising: illuminating the gas with a periodically modulated light source, wherein a first indication of time and a second indication of time indicate times when a gas is not illuminated by the periodically modulated light source; receiving a first output signal from a pressure sensor, the first output signal associated with a first known concentration of the gas, wherein the pressure sensor is part of the photoacoustic sensor system; receiving a second output signal from the pressure sensor, the second output signal associated with a second known concentration of the gas, wherein the first output signal and the second output signal have a same value at a third indication of time (302A, 302B) between the first indication of time and the second indication of time; determining a first slope of the first output signal from a first value of the first output signal at the first indication of time and a second value of the first output signal at the second indication of time; determining a second slope of the second output signal from a first value of the second output signal at the first indication of time and a second value of the second output signal at the second indication of time; and calibrating the photoacoustic sensor system by determining a correlation between the slope of an output signal and the concentration of the gas based on the first slope, the second slope, the first known concentration, and the second known concentration, wherein determining the correlation comprises determining parameters of a linear relationship between the slope of an output signal and the concentration of the gas based on the first slope and the first known concentration (C1, K1), and based on the second slope and the second known concentration (C2, K2). illuminating the gas with a periodically modulated light source, wherein a first indication of time and a second indication of time indicate times when a gas is not illuminated by the periodically modulated light source; receiving a first output signal from a pressure sensor, the first output signal associated with a first known concentration of the gas, wherein the pressure sensor is part of the photoacoustic sensor system; receiving a second output signal from the pressure sensor, the second output signal associated with a second known concentration of the gas, wherein the first output signal and the second output signal have a same value at a third indication of time (302A, 302B) between the first indication of time and the second indication of time; determining a first slope of the first output signal from a first value of the first output signal at the first indication of time and a second value of the first output signal at the second indication of time; determining a second slope of the second output signal from a first value of the second output signal at the first indication of time and a second value of the second output signal at the second indication of time; and calibrating the photoacoustic sensor system by determining a correlation between the slope of an output signal and the concentration of the gas based on the first slope, the second slope, the first known concentration, and the second known concentration, wherein determining the correlation comprises determining parameters of a linear relationship between the slope of an output signal and the concentration of the gas based on the first slope and the first known concentration (C1, K1), and based on the second slope and the second known concentration (C2, K2).