Heterogeneous uptake of ammonia and dimethylamine into sulfuric and oxalic acid particles

Abstract

<p><strong>Abstract.</strong> Heterogeneous uptake is one of the major mechanisms governing the amounts of short-chain alkyl-amines and ammonia (NH<sub>3</sub>) gases resident in atmospheric particles. Molar ratios of aminium to ammonium ions detected in ambient aerosols often exceed typical gas phase ratios. The present study investigated the simultaneous uptake of dimethylamine (DMA) and NH<sub>3</sub> into sulfuric and oxalic acid particles at gaseous DMA/NH<sub>3</sub> molar ratios of 0.1 and 0.5 at 10 %, 50 %, and 70 % relative humidity (RH). Single gas uptake and co-uptake were conducted under identical conditions and compared. Results showed that the particulate dimethyl-aminium/ammonium molar ratios (DMAH/NH<sub>4</sub>) changed substantially during the uptake process, which was predominantly influenced by the extent of neutralization and the particle phase state. DMA uptake and NH<sub>3</sub> uptake into concentrated H<sub>2</sub>SO<sub>4</sub> droplets were initially similarly efficient, yielding DMAH/NH<sub>4</sub> that were similar to DMA/NH<sub>3</sub> ratios. As the co-uptake continued the DMAH/NH<sub>4</sub> gradually dropped due to a preferential uptake of NH<sub>3</sub> into still acidic droplets. Once the droplets were neutralized, the stronger base DMA displaced some of the ammonium absorbed earlier, leading to DMAH/NH<sub>4</sub> that were up to four times higher than the corresponding gas phase ratios. At 10 % RH, crystallization of partially neutralized sulfate particles prevented further DMA uptake, while NH<sub>3</sub> uptake continued, and displaced DMAH<sup>+</sup> after the solid particles were completely neutralized, forming almost pure ammonium sulfate. Displacement of DMAH<sup>+</sup> by NH<sub>3</sub> has also been observed in neutralized, solid oxalate particles. The results illustrate why in ambient liquid aerosols the DMAH/NH<sub>4</sub> can be larger than DMA/NH<sub>3</sub>, despite of an excess of NH<sub>3</sub> in the gas phase; the uptake of DMA to aerosols consisting of crystalline ammonium salts, however is unlikely, even if the gas concentrations of DMA and NH<sub>3</sub> are of the same magnitude.</p>

Large Increases in Primary Trimethylaminium and Secondary Dimethylaminium in Atmospheric Particles Associated With Cyclonic Eddies in the Northwest Pacific Ocean

“…In the literature, the particle mode of species at 0.4 μm may be associated with either primary combustion emissions or heterogeneous reactions (Ondov & Wexler, ; Xie et al, ). Assuming that the DMA + over the NWPO is derived mainly from oceanic sources, the latter likely formed the DMA + mode at 0.4 ± 0.1 μm through an acid‐base neutralization reaction between the gaseous amines and acidic particles (Sauerwein & Chan, ; Xie et al, ).…”

Role of oleic acid coating in the heterogeneous uptake of dimethylamine by ammonium sulfate particles

“…) salts is one of the major pathways for the gas-to-particle partitioning of short-chain alkyl amines, which are important alkaline gases in addition to ammonia (NH 3 ) in the atmosphere. The reaction mechanism of NH 4 C displacement by alkyl aminium has been confirmed using a wide range of gasphase amine concentrations (Lloyd et al 2009;Bzdek et al 2010;Chan and Chan 2012;Sauerwein and Chan 2016). The phase state of individual ammonium salts can influence the extent of amine uptake: ammonium salts in aqueous or amorphous solid form lead to higher amine uptake than those in crystalline solid form (Chan and Chan 2013).…”

Heterogeneous SO2 Oxidation in Sulfate Formation by Photolysis of Particulate Nitrate

“…It has been demonstrated to be useful for studying heterogeneous reactions of aerosols such as the reactive uptake of ammonia, dimethylamine, and glyoxal. 10,31 SO 2 (7.7 ppm) in N 2 or air was introduced into the flow cell. The heterogeneous oxidation of SO 2 was initiated by UV irradiation using a low-pressure mercury UV lamp (254 nm; Pen-Ray, UVP).…”