Light absorption coefficient measurement of SOA using a UV-Visible spectrometer connected with an integrating sphere

A method for measuring an aerosol light absorption coefficient (B-a) has been developed using a conventional UV-visible spectrometer equipped with an integrating sphere covering a wide range of wavelengths (280-800 nm). The feasibility of the proposed method was evaluated in both the transmittance mode (TUV-IS) and the reflective mode (RUV-IS) using the reference aerosol known for the cross-sectional area. The aerosol was collected on a conventional filter and measured for B-a values. The resulting RUV-IS method was applied to measure light absorption of secondary organic aerosol (SOA). SOA was produced through photooxidation of different precursor hydrocarbons such as toluene, d-limonene and a-pinene in the presence of NOx (60-70 ppb) and inorganic seed aerosol using a 2-m(3) indoor Teflon film chamber. Of the three precursor hydrocarbons, the B-a value of toluene SOA (0.574 m(2) g(-1) at 350 nm) was the highest compared with B-a values for a-pinene SOA (0.029 m(2) g(-1)) and d-limonene SOA (0.038 m(2) g(-1)). When d-limonene SOA or toluene SOA was internally mixed with neutral [(NH4)(2)SO4] or acidic inorganic seed (NH4HSO4:H2SO4 = 1:1 by mole), the SOA showed 2-3 times greater B-a values at 350 nm than the SOA with no seed. Aerosol aging with a light source for this study reduced B-a values of SOA (e.g., on average 10% for toluene SOA and 30% for d-limonene SOA within 4 h). Overall, weak absorption appeared for chamber-generated SOA over wavelengths ranging from 280 to 550 nm, which fall into the sunlight spectrum. (C) 2011 Elsevier Ltd. All rights reserved.