Aging of mineral dusts and proxies by uptake of methylglyoxal: A Knudsen cell study

This study investigates interactions between methylglyoxal (MGL) and 29 different samples, such as clays, proxies and natural dusts from the arid regions of the planet. Initial and quasi steady state uptake coefficients (ɣ0 and ɣqss) of MGL are determined using a Knudsen cell at concentration of 70 ppb, under dry conditions. Remarkably high ɣ0 values for MGL, ranging from 0.05 to 0.67, are determined, close to those of radical species, suggesting a high affinity for dusts. ɣ0 is evidenced to be linearly correlated with the Al/Si ratio of dust samples, indicating a specific initial affinity of MGL with aluminum surface sites. Ɣqss, determined after 40 min of exposure, ranges from 2.9 × 10−7 to 5.9 × 10−6. Ɣqss is linearly correlated with Ti/Si ratio, highlighting specific affinity of MGL with titanium. The impact of concentration on ɣqss is investigated on Gobi dust with MGL concentrations ranging from 0.1 ppt to 2.2 ppm. Ɣqss increases when MGL concentration decreases. Under typical dust storm conditions, MGL uptake competes with gas phase removal by OH radicals or photolysis. In addition, the maximum storage capacity of MGL by samples is determined at 2 ppm with Knudsen cell. MGL uptake does not exceed a compact monolayer on natural dust samples, whereas on some surrogates multilayer uptake is reached. Comparison of ɣ0 and ɣqss of glyoxal and MGL shows that MGL generally exhibits higher affinity with samples. The maximum number of molecules taken up by Gobi dust (Nmax) of MGL is compared with those for isoprene, isopropanol and acetic acid retrieved from literature. It points at the dependance of Nmax on chemical functionality of VOCs: oxygenated compounds exhibit higher interactions with dust. Data are available to increase the representativeness of modeling. •Uptake coefficient of methylglyoxal on mineral surfaces is high and irreversible.•Dust composition (Al/Si and Ti/Si ratios) is corelated with methylglyoxal uptake.•On gobi dust, steady state uptake coefficient depends on methylglyoxal concentration.•Mineral dust can be a significant sink of methylglyoxal leading to SOA formation.•This work provides kinetic data to improve model simulations.