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While brown carbon (BrC) might play a substantially important role in radiative forcing, an estimation of its light absorption contribution with high-time resolution is still challenging. In this study, a multi-wavelength (370-950 nm) Aethalometer was applied to obtain the wavelength dependent light absorption coefficient (sigma(abs)) of aerosols both before and after being heated to 250 degrees C. An improved absorption angstrom ngstrom exponent (AAE)-based method was developed to evaluate the contribution of BrC to light absorption at a wavelength of 370 nm (sigma(abs,BrC)/sigma(abs,370nm)). The sigma(abs,BC) at 370 nm was determined from the field measured AAE values for the wavelengths from 880 to 950 nm with a one-hour resolution. The simultaneous measurements of heated aerosols help confirm the negligible influence of BrC on the sigma(abs) values across the range of 880-950 nm. Meanwhile, sigma(abs,BrC)/sigma(abs,370nm) was also estimated with previously reported methods by assuming that the AAE was equal to 1 (Method I) as well as a new approach based on the light absorption enhancement (Method II). While the estimated sigma(abs,BrC)/sigma(abs,370nm) based on our developed method and Method I is highly correlated (r(2) = 0.78), the difference could be as large as > 20% on average. The obtained mean sigma(abs,BrC)/sigma(abs,370nm) was negative with Method II, a indicating the net production of BrC when the aerosols were heated. The difference between the values for sigma(abs,BrC)/sigma(abs,370nm) obtained by our developed method and by Method II was similar to 40% on average and much higher (> 50%) during the noon hour, when secondary organic aerosols and sulfate were abundant. We propose that it is more suitable to use an AAE around 0.7 for pure BC to evaluate the contribution of BrC to light absorption in the PRD region. The developed method thus helps improve our understanding of the light absorption and climate forcing of BrC.

来源平台：AEROSOL AND AIR QUALITY RESEARCH