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

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