Degradation of Dicarboxylic Acids (C2−C9) upon Liquid-Phase Reactions with O3 and Its Atmospheric Implications

Aerosols are considered major players in climate change and represent health hazards. Dicarboxylic acids are among a major class of components that form secondary organic atmospheric aerosols. To understand the atmospheric transformation of these compounds, kinetic studies on the ozonolysis and the photoinduced ozonolysis (λ ≥ 250 nm) of aqueous solutions of seven (C2−C9) dicarboxylic acids, which have been identified in atmospheric aerosols, were performed using Fourier transform infrared and ultraviolet−visible spectroscopy. The measured apparent rate constants for dicarboxylic acids in 0.1 mol L-1 aqueous solutions at 298 ± 2 K are as follows: oxalic, (2.7 ± 0.1) × 10-2; malonic, (5.5 ± 0.1); succinic, (6.7 ± 0.4) × 10-4; glutaric, (1.3 ± 0.2) × 10-3; adipic, (1.7 ± 0.1) × 10-3; pimelic, (4.4 ± 0.1) × 10-3; and pinic, (2.5 ± 0.1) × 10-2 (L mol-1 s-1). An empirical equation is provided to estimate the ozonolysis rate constant of dicarboxylic acids containing more than three carbon atoms for which no experimental data exists. A mechanism for malonic acid ozonolysis, which explains its fast ozonolysis rate constant, is also suggested. The implications of our results to atmospheric chemistry indicate that ozonolysis and photoinduced ozonolysis are not significant removal pathways for dicarboxylic acids.