Abstract
Abstract. Alpha-dicarbonyl compounds are believed to form brown carbon in the atmosphere via reactions with ammonium sulfate (AS) in cloud droplets and aqueous aerosol particles. In this work, brown carbon formation in AS and other aerosol particles was quantified as a function of relative humidity (RH) during exposure to gas-phase glyoxal (GX) in chamber experiments. Under dry conditions (RH < 5 %), solid AS, AS–glycine, and methylammonium sulfate (MeAS) aerosol particles brown within minutes upon exposure to GX, while sodium sulfate particles do not. When GX concentrations decline, browning goes away, demonstrating that this dry browning process is reversible. Declines in aerosol albedo are found to be a function of [GX]2 and are consistent between AS and AS–glycine aerosol. Dry methylammonium sulfate aerosol browns 4 times more than dry AS aerosol, but deliquesced AS aerosol browns much less than dry AS aerosol. Optical measurements at 405, 450, and 530 nm provide an estimated Ångstrom absorbance coefficient of -16±4. This coefficient and the empirical relationship between GX and albedo are used to estimate an upper limit to global radiative forcing by brown carbon formed by 70 ppt GX reacting with AS (+7.6×10-5 W m−2). This quantity is < 1 % of the total radiative forcing by secondary brown carbon but occurs almost entirely in the ultraviolet range.
Highlights
Brown carbon is the name given to light-absorbing organic molecules present in atmospheric aerosol
We report rapid and reversible browning of dry ammonium sulfate (AS), AS–glycine, and methylammonium sulfate (MeAS) aerosol particles upon exposure to gasphase glyoxal
Aerosol particles were sampled via diffusion driers by a quadrupole aerosol mass spectrometer (Q-AMS; Aerodyne), CAPS-ssa (Aerodyne, 450 nm), scanning mobility particle sizing (SMPS) (TSI), cavity ring-down (CRD) (405 and 530 nm; Ugelow et al, 2017), and photoacoustic spectrometers (PASs; 405 and 530 nm; Ugelow et al, 2017), all of which were periodically baselined through filters to eliminate interferences by gas-phase species
Summary
Brown carbon is the name given to light-absorbing organic molecules present in atmospheric aerosol. Estimates of the global direct radiative effect of brown carbon aerosol range from +0.05 to 0.27 W m−2 (Tuccella et al, 2020; Laskin et al, 2015; Zhang et al, 2020; Wang et al, 2018). This absorption occurs mainly at ultraviolet (UV) and near-UV wavelengths, suppressing photochemistry in areas with high loadings (Mok et al, 2016). We report rapid and reversible browning of dry ammonium sulfate (AS), AS–glycine, and methylammonium sulfate (MeAS) aerosol particles upon exposure to gasphase glyoxal. This browning process is not accompanied by appreciable particle growth and is reversed upon addition of water vapor
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
