The optical, physical and chemical properties of the products of glyoxal uptake on ammonium sulfate seed aerosols

Abstract

Abstract. The heterogeneous reaction between gas phase glyoxal and ammonium sulfate (AS) aerosols, a proxy for inorganic atmospheric aerosol, was studied in terms of the dependence of the optical, physical and chemical properties of the product aerosols on initial particle size and ambient relative humidity (RH). Our experiments imitate an atmospheric scenario of a dry particle hydration at ambient RH conditions in the presence of glyoxal gas followed by efflorescence due to decrease of the ambient RH. The reactions were studied under different RH conditions, starting from dry conditions (∼20 % RH) and up to 90 % RH, covering conditions prevalent in many atmospheric environments, and followed by consequent drying of the reacted particles before their analysis by the aerosol mass spectrometer (AMS), cavity ring down (CRD) and scanning mobility particle sizer (SMPS) systems. At λ = 355 nm, the reacted aerosols demonstrate a substantial growth in optical extinction cross section, as well as in mobility diameter under a broad range of RH values (35-90 %). The ratio of the product aerosol to seed aerosol geometric cross section reached up to ∼3.5, and the optical extinction cross-section up to ∼250. The reactions show a trend of increasing physical and optical growth with decreasing seed aerosol size, from 100 nm to 300 nm, as well as with decreasing RH values from 90 % to ∼40 %. Optically inactive aerosols, at the limit of the Mie range (100 nm diameter) become optically active as they grow due to the reaction. AMS analyses of the reaction of 300 nm AS at RH values of 50 %, 75 % and 90 % show that the main products of the reaction are glyoxal oligomers, formed by acetal formation in the presence of AS. In addition, imidaCorrespondence to: Y. Rudich (yinon.rudich@weizmann.ac.il) zole formation, which is a minor channel, is observed for all reactions, yielding a product which absorbs at λ = 290 nm, with possible implications on the radiative properties of the product aerosols. The ratio of absorbing substances (C-N compounds, including imidazoles) increases with increasing RH value. A core/shell model used for the investigation of the optical properties of the reaction products of AS with gas phase glyoxal, shows that the refractive index (RI) of the reaction products are n = 1.68(±0.10) + 0.01(±0.02) at 50 % RH and n = 1.65(±0.06) + 0.02(±0.01) at 75 % RH at 355 nm. The observed increase in the ratio of the absorbing substances is not indicated in the imaginary part of the products at RH 50 % and 75 %. A further increase in the ratio of absorbing substances and a resulting increase in the imaginary part of the RI at higher RH values is expected, and may become even more substantial after longer reaction times, possibly in cloud or fog droplets. This study shows that the reaction of abundant substances present in atmospheric aerosols, such as AS, and gas phase glyoxal alters the aerosols' optical, physical and chemical properties and may have implications on the radiative effect of these aerosols.

Broadband measurements of aerosol extinction in the ultraviolet spectral region

“…Hence, the optical properties of AS are important to atmospheric radiative transfer models and to calculations of climatic Spindler et al, 2007;Lang-Yona et al, 2009;Flores et al, 2009) Toon et al (1976) reported a real value of n = 1.53-1.55 and an imaginary value of k < 1 × 10 −7 determined from the reflectivity and transmission of crystalline ammonium sulfate samples. Our results are consistent with these prior measurements, with the exception of Trainic et al (2011), as shown in Fig. 6.…”

Secondary organic aerosol formation from semi‐ and intermediate‐volatility organic compounds and glyoxal: Relevance of O/C as a tracer for aqueous multiphase chemistry

“…A surface-limited process is found to best reproduce the time evolution of the glyoxal imbalance with an uptake coefficient, g = 0.0033, consistent with laboratory data [Liggio et al, 2005;Trainic et al, 2011]. For the bulk reaction case, the GLY-SOA product distribution depends strongly on the Henry's law constant of glyoxal and particle pH, and less on the gas-phase OH radical concentration.…”

Brown carbon formation from ketoaldehydes of biogenic monoterpenes

“…They form by different mechanisms than the imidazole-based oligomers previously linked to secondary brown carbon in the atmospheric chemistry literature. [7][8][9][10]33,34 As the chemistry that produces brown carbon is diverse, the structures of the chromophoric compounds may be similarly varied in nature.…”

“…[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.…”