Uptake of methylglyoxal on a diversity of natural mineral dusts and proxies: Heterogeneous kinetics and uptake mechanism

Atmospheric aerosols are drivers of climate. Their impact is direct by scattering or absorbing solar radiation, and indirect, by serving as cloud condensation and ice nuclei. Once released into the atmosphere, aerosols can interact and/or react with gas-phase species thereby initiating a process known as chemical aging. This process tends to modify their surfaces. Mineral dust constitutes a significant part of the global atmospheric aerosol mass budget, contributing to almost half of the yearly particle emissions. Dust particles can traverse considerable distances, impacting remote areas from their sources. Despite the pivotal role of mineral dust in the atmosphere, considerable uncertainties persist regarding their influence on climate and air quality. This uncertainty primarily stems from a limited understanding of the fate of dust in the atmosphere and the underlying chemical processes they induce.

The aim of this work is to explore the heterogeneous interaction of methylglyoxal (MGL) with natural mineral dust. MGL results from the oxidation of isoprene in the atmosphere and is regarded as a crucial precursor to secondary organic aerosols (SOA). Therefore, its atmospheric fate of significant consequence to Earth's climate. Uptake experiments were conducted in a Knudsen flow reactor, operating in the molecular flow regime, and coupled with a modulated molecular beam quadrupole mass spectrometer for real-time monitoring of gas-phase reactants and products. The uptake coefficients of MGL is determined on 29 different mineralogical origin surfaces, to elucidate the impact of chemical composition on the uptake efficiency of the dusts.  

The initial uptake coefficients, γ₀,is determined to range from 0.05 to 0.67. These values are in the same order of magnitude than reactive gases in the atmosphere, indicating a high affinity between MGL and mineral dust. A correlation between γ₀ and Al/Si ratio of natural dust sample is evidenced and discussed. Furthermore, focusing on natural Gobi desert dust, the impact of MGL concentration (0.1 to 2,200 ppb) on γ_qss is determined. γ_qss increases as MGL concentration is decreased. Results revealed that the heterogeneous loss of MGL on dusts is a major atmospheric sink comparable to its gas-phase oxidation or photolysis. In addition, MGL uptake mechanism is studied on Gobi dust using in-situ DRIFT (Diffuse Reflectance Infrared Fourier transform) spectroscopy, providing useful information on interaction mechanisms. These findings offer novel insights into the atmospheric fate of MGL, providing a more comprehensive understanding of its heterogeneous atmospheric fate.