Reactive uptake of glyoxal by particulate matter

Abstract

The uptake of gaseous glyoxal onto particulate matter has been studied in laboratory experiments under conditions relevant to the ambient atmosphere using an aerosol mass spectrometer. The growth rates and reactive uptake coefficients, γ, were derived by fitting a model of particle growth to the experimental data. Organic growth rates varied from 1.05 × 10−11 to 23.1 × 10−11 μg particle−1 min−1 in the presence of ∼5 ppb glyoxal. Uptake coefficients (γ) of glyoxal varied from 8.0 × 10−4 to 7.3 × 10−3 with a median γ = 2.9 × 10−3, observed for (NH 4)2 SO 4 seed aerosols at 55% relative humidity. Increased γ values were related to increased particle acidity, indicating that acid catalysis played a role in the heterogeneous mechanism. Experiments conducted at very low relative humidity, with the potential to be highly acidic, resulted in very low reactive uptake. These uptake coefficients indicated that the heterogeneous loss of glyoxal in the atmosphere is at least as important as gas phase loss mechanisms, including photolysis and reaction with hydroxyl radicals. Glyoxal lifetime due to heterogeneous reactions under typical ambient conditions was estimated to be τ het = 5–287 min. In rural and remote areas the glyoxal uptake can lead to 5–257 ng m−3 of secondary organic aerosols in 8 hours, consistent with recent ambient measurements.