Brown Carbon Spheres in East Asian Outflow and Their Optical Properties

Abstract

Atmospheric aerosols play a substantial role in climate change through radiative forcing. Combustion-produced carbonaceous particles are the main light-absorbing aerosols; thus, quantifying their optical properties is essential for determining the magnitude of direct forcing. By using the electron energy-loss spectrum in the transmission electron microscope, we quantified the optical properties of individual, submicrometer amorphous carbon spheres that are ubiquitous in East Asian-Pacific outflow. The data indicate that these common spheres are brown, not black, with a mean refractive index of 1.67 - 0.27i (where i = square root 1) at a wavelength of 550 nanometers. The results suggest that brown carbon aerosols should be explicitly included in radiative forcing models.

Brown carbon formation from ketoaldehydes of biogenic monoterpenes

“…However, the relative DMAC values can be determined with greater accuracy by keeping the evaporation conditions identical for a series of different samples. For example, the GLY-aged KLA has systematically higher DMAC than NH 4 + -aged KLA.…”

“…[5][6][7]9,32,33 As such, the active brown-carbon precursors in the limonene/O 3 SOA mixture have yet to be identied. The study of and related studies 5,8,10,26,27,34 offer important insights on the nature of the chromophore structure and the NH 4 + -mediated reaction. These studies suggest that the chromophores likely contain a pC]N-(imine) motif in their structures.…”

“…Although aging of a lm with humid NH 3 vapour produces similar chromophores to those formed in evaporative aging, 25 it is much slower and may be limited by the surface area of the lm. However, this method of aging eliminates interference from the inorganic additives, for example, the interfering bands such as the strong NH bending modes of NH 4 + (expected at $1400 cm À1 )…”

“…Brown carbon can be directly emitted from combustion sources 2-4 as part of POA or created by reactions in the atmosphere, such as in the formation or aging of SOA. This secondary brown carbon can be formed from multiple precursors and a variety of reaction pathways, e.g., the reactions of 1,2-dicarbonyls with ammonium (NH 4 + ) salts, 5-10 the aqueous photooxidation of hydroxyacids, [11][12][13] the acid-catalysed condensation of volatile aldehydes, [14][15][16][17][18][19][20][21] and the nitration of aromatic compounds.…”

Truncation and Angular-Scattering Corrections for Absorbing Aerosol in the TSI 3563 Nephelometer

“…Recognition of this latter material as a component of atmospheric aerosol is growing Alexander et al 2008). …”