Use of ward closure to control outbreaks among hospitalized patients in acute care settings: a systematic review

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Brown Carbon Formation by Aqueous-Phase Carbonyl Compound Reactions with Amines and Ammonium Sulfate

Reactions between small water-soluble carbonyl compounds, ammonium sulfate (AS), and/or amines were evaluated for their ability to form light-absorbing species in aqueous aerosol. Aerosol chemistry was simulated with bulk phase reactions at pH 4, 275 K, initial concentrations of 0.05 to 0.25 M, and UV–vis and fluorescence spectroscopy monitoring. Glycolaldehyde–glycine mixtures produced the most intense absorbance. In carbonyl compound reactions with AS, methylamine, or AS/glycine mixtures, product absorbance followed the order methylglyoxal \u3e glyoxal \u3e glycolaldehyde \u3e hydroxyacetone. Absorbance extended into the visible, with a wavelength dependence fit by absorption Ångstrom coefficients (Åabs) of 2 to 11, overlapping the Åabs range of atmospheric, water-soluble brown carbon. Many reaction products absorbing between 300 and 400 nm were strongly fluorescent. On a per mole basis, amines are much more effective than AS at producing brown carbon. In addition, methylglyoxal and glyoxal produced more light-absorbing products in reactions with a 5:1 AS-glycine mixture than with AS or glycine alone, illustrating the importance of both organic and inorganic nitrogen in brown carbon formation. Through comparison to biomass burning aerosol, we place an upper limit on the contribution of these aqueous carbonyl–AS–amine reactions of ≤10% of global light absorption by brown carbon

Formaldehyde and Acetaldehyde Increase Aqueous-Phase Production of Imidazoles in Methylglyoxal/Amine Mixtures: Quantifying a Secondary Organic Aerosol Formation Mechanism

Formaldehyde and acetaldehyde are commonly found in cloud droplets because of reversible partitioning and hydration reactions. An SOA formation pathway was recently identified in which these common aldehydes are irreversibly incorporated into imidazole derivatives formed by reaction with dicarbonyl species and ammonium salts or amine species. Here we use ultraviolet–visible and nuclear magnetic resonance kinetic measurements to determine the influence of formaldehyde and acetaldehyde on aqueous methylglyoxal chemistry. The presence of formaldehyde increases imidazole product formation rates by factors of 2 and ≥5 in reactions with ammonium sulfate and amines, respectively, and increases imidazole product yields in methylglyoxal + amine reactions by more than an order of magnitude. Acetaldehyde is less likely to be incorporated into imidazole products and increases formation rates and yields only in reactions involving amines. We estimate that aqueous formation of imidazoles could generate as much as 1.05 Tg of C/year SOA from formaldehyde and 3.8 Tg of C/year or 7 Tg/year SOA overall, limited by the availability of aqueous-phase glyoxal and methylglyoxal. While this upper limit represents a negligible formaldehyde sink, it is ∼5% of current estimates of global SOA formation. Formaldehyde’s channeling of aqueous dicarbonyl chemistry toward production of imidazoles limits the formation of other oligomer products, including brown carbon species