A single-beam photothermal interferometer for in situ measurements of aerosol light absorption

We have developed a novel single-beam photothermal interferometer and present here its application for the measurement of aerosol light absorption. The use of only a single laser beam allows for a compact optical set-up and significantly easier alignment compared to standard dualbeam photothermal interferometers, making it ideal for field measurements. Due to a unique configuration of the reference interferometer arm, light absorption by aerosols can be determined directly - even in the presence of light-absorbing gases. The instrument can be calibrated directly with light-absorbing gases, such as NO2, and can be used to calibrate other light absorption instruments. The detection limits (1 sigma) for absorption for 10 and 60 s averaging times were determined to be 14.6 and 7.4Mm(-1), respectively, which for a mass absorption cross section of 10m(2) g(-1) of 1460 and 740 ng m(-3), respectively. The detection limit could be reduced further by improvements to the isolation of the instrument and the signal detection and processing schemes employed.