Aerosol Light Absorption and Scattering Coefficient Measurements with a Photoacoustic and Nephelometric Spectrometer

Abstract

Ambient measurements of aerosol light absorption (σ a) and scattering coefficients (σ s) were done at Gosan climate observatory during summer 2008 using a 3-wavelength photo-acoustic soot spectrometer (PASS). PASS was deployed photoacoustic method for light absorption and integrated nephelometry for light scattering measurements. The σ a and σ s from PASS were compared with those from co-located aethalometer and nephelometer measurements. The aethalometer measurements of σ a correlated reasonably well with photoacoustic measurements , but the slope of the linear fitting line indicated the PASS measurement values of σ a were larger by a factor of 1.53. The nephelometer measurement values of σ s correlated very well with PASS measurements of σ s , with a slope of 1.12 and a small offset. Comparing to the aethalometer measurements, the photoacoustic measurements of σ a didn't exhibit a significant (i.e., the ratio between aethalometer and PASS increased) change with increasing relative humidity (RH). The ratio of σ s between nephelometer and PASS increased with increasing RH, especially when the RH increased beyond 80%. This apparent increase in σ s with RH may be due to the contribution of hygroscopic growth of aerosols.