Secondary organic aerosol-forming reactions of glyoxal with amino acids

Glyoxal, the simplest and most abundant alpha-dicarbonyl compound in the atmosphere, is scavenged by clouds and aerosol, where it reacts with nucleophiles to form low-volatility products. Here we examine the reactions of glyoxal with five amino acids common in clouds. When glyoxal and glycine, serine, aspartic acid or ornithine are present at concentrations as low as 30/microM in evaporating aqueous droplets or bulk solutions, 1,3-disubstituted imidazoles are formed in irreversible second-order reactions detected by nuclear magnetic resonance (NMR), aerosol mass spectrometry (AMS) and electrospray ionization mass spectrometry (ESI-MS). In contrast, glyoxal reacts with arginine preferentially at side chain amino groups, forming nonaromatic five-membered rings. All reactions were accompanied by browning. The uptake of 45 ppb glyoxal by solid-phase glycine aerosol at 50% RH was also studied and found to cause particle growth and the production of imidazole measured by scanning mobility particle sizing and AMS, respectively, with a glyoxal uptake coefficient alpha = 0.0004. Comparison of reaction kinetics in bulk and in drying droplets shows that conversion of glyoxal dihydrate to monohydrate accelerates the reaction by over 3 orders of magnitude, allowing these reactions to occur at atmospheric conditions.

East China plains: a "basin" of ozone pollution

Economic growth and associated pollution emissions in China are concentrated over three connected plains to the east In this work, we analyze an episode of highly elevated ozone over East China on June 9-14, 2004, using a 3-D chemical transport model. During this episode, the East China plains were under a high-pressure system, which suppressed the ventilation of pollutants from the boundary layer. Simulated ozone concentrations over a major fraction of East China reached high levels, all the way down to the Pearl River Delta region in the southern border. The convergence of pollutant emissions and population over the vast stretch of the geographically flat plains of East China makes the region susceptible to high-ozone exposure. During this episode, the high-03 region extended over an area >1 million km2, which hosts a population of >800 million people. Model results indicate that controlling anthropogenic NOx emissions effectively reduces the area with high-ozone exposure.