Chemistry of Atmospheric Brown Carbon

Abstract

<p>Fundamental understanding of the complex chemistry of light absorbing atmospheric aerosols (aka Brown Carbon - BrC), their physico-chemical properties and environmental impacts is a challenging task because no single method of analytical chemistry is capable of providing the full range of analytical chemistry information. Micro-spectroscopy approaches can visualize individual particles and their internal structures; however, they largely exclude molecular-level information, and are limited to elemental and chemical bonding characterization. Contemporary methods of high-resolution mass spectrometry can provide detailed information on the molecular content of BrC, but these methods use bulk particle samples and provide no knowledge of the individual particle composition. Therefore, application of complementary analytical methods of chemical analysis is necessary for comprehensive characterization of aerosol properties ranging from bulk molecular composition of BrC constituents to microscopy level details of individual particles. Combined assessment of the results provided by complementary analytical chemistry techniques offers unique insights to understand the composition and physico-chemical properties of BrC aerosols determining their effects on air quality and climate. This presentation will give an overview of recent field and laboratory studies of BrC with an overall goal to understand fundamental relationship between chemical transformations of airborne particles and their environmental and climate impacts.</p>

Aerosols in atmospheric chemistry and biogeochemical cycles of nutrients

“…Recent laboratory investigations have shown that photosensitizers can initiate aerosol growth in the presence of gaseous volatile organic compounds, in particular the imidazole derivatives, like imidazole-2 carboxaldehyde, that are formed by reaction of glyoxal with ammonium cations (Rossignol et al 2014). Dark reactions including acid-catalyzed aerosol chemistry of hydronium or ammonium ions, which protonate epoxide and carbonyl groups thus enabling attack by nucleophiles such as water, SO 4 2− , NH 3 and NO 3 − , may be responsible for the ring opening mechanism of epoxides, organosulfate formation by epoxides and carbonyls and C-N-containing lightabsorbing organic species as part of the 'brown carbon' pool (Surratt et al 2010, McNeill 2015, Laskin et al 2015. Night-time chemistry driven by NO 3 radicals also produces organic nitrogen in the aerosol phase that was found to be 5%-12% of OAs during the summer months (Xu et al 2015a).…”

UV–Vis–IR spectral complex refractive indices and optical properties of brown carbon aerosol from biomass burning

“…A: Values of n show no significant dependence on λ, are constrained between 1.5 and 1.7, and are independent of the source depth, MC, and geographic origin. B: κ decreases monotonically with λ between 375 and 532 nm, above which it levels off at κ ≈ 0.002.The current understanding of BrC optical properties has been summarized in previous work, notably byLiu et al (2015) andLaskin et al (2015) [7,29]. Liu et al compared the wavelengthdependent κ values for a variety of atmospheric light absorbing organic material such as m-xylene and toluene oxidation products…”

Aerosol light absorption from optical measurements of PTFE membrane filter samples: sensitivity analysis of optical depth measures

“…Our findings underscore that OD s is a better optical depth measure than OD c for applying appropriate correction factors when estimating particle-phase light absorption from filter-based techniques. combustion phase and can range ∼ 0.01-1 m 2 g −1 at 550 nm (Laskin et al, 2015).…”