Temperature-Dependent Oxidation of Hydroxylated Aldehydes by ^•OH, SO₄^•–, and NO₃^• Radicals in the Atmospheric Aqueous Phase

Abstract

T -dependent aqueous-phase rate constants were determined for the oxidation of the hydroxy aldehydes, glyceraldehyde, glycolaldehyde, and lactaldehyde, by the hydroxyl radicals ( • OH), the sulfate radicals (SO 4 •– ), and the nitrate radicals (NO 3 • ). The obtained Arrhenius expressions for the oxidation by the • OH radical are: k (T,GLYCERALDEHYDE+OH • ) = (3.3 ± 0.1) × 10 10 × exp((−960 ± 80 K)/ T )/L mol –1 s –1, k (T,GLYCOLALDEHYDE+OH • ) = (4.3 ± 0.1) × 10 11 × exp((−1740 ± 50 K)/ T )/L mol –1 s –1, k (T,LACTALDEHYDE+OH • ) = (1.6 ± 0.1) × 10 11 × exp((−1410 ± 180 K)/ T )/L mol –1 s –1; for the SO 4 •– radical: k (T,GLYCERALDEHYDE+SO 4 •– ) = (4.3 ± 0.1) × 10 9 × exp((−1400 ± 50 K)/ T )/L mol –1 s –1, k (T,GLYCOLALDEHYDE+SO 4 •– ) = (10.3 ± 0.3) × 10 9 × exp((−1730 ± 190 K)/ T )/L mol –1 s –1, k (T,LACTALDEHYDE+SO 4 •– ) = (2.2 ± 0.1) × 10 9 × exp((−1030 ± 230 K)/ T )/L mol –1 s –1; and for the NO 3 • radical: k (T,GLYCERALDEHYDE+NO 3 • ) = (3.4 ± 0.2) × 10 11 × exp((−3470 ± 460 K)/ T )/L mol –1 s –1, k (T,GLYCOLALDEHYDE+NO 3 • ) = (7.8 ± 0.2) × 10 11 × exp((−3820 ± 240 K)/ T )/L mol –1 s –1, k (T,LACTALDEHYDE+NO 3 • ) = (4.3 ± 0.2) × 10 10 × exp((−2750 ± 340 K)/ T )/L mol –1 s –1, respectively. Targeted simulations of multiphase chemistry reveal that the oxidation by OH radicals in cloud droplets is important under remote and wildfire influenced continental conditions due to enhanced partitioning. There, the modeled average aqueous • OH concentration is 2.6 × 10 –14 and 1.8 × 10 –14 mol L –1, whereas it is 7.9 × 10 –14 and 3.5 × 10 –14 mol L –1 under wet particle conditions. During cloud periods, the aqueous-phase reactions by • OH contribute to the oxidation of glycolaldehyde, lactaldehyde, and glyceraldehyde by about 35 and 29%, 3 and 3%, and 47 and 37%, respectively.