Importance of secondary sources in the atmospheric budgets of formic and acetic acids.

We present a detailed budget of formic and acetic acids, two of the most abundant trace gases in the atmosphere. Our bottom-up estimate of the global source of formic and acetic acids are ∼1200 and ∼1400Gmolyr-1, dominated by photochemical oxidation of biogenic volatile organic compounds, in particular isoprene. Their sinks are dominated by wet and dry deposition. We use the GEOS-Chem chemical transport model to evaluate this budget against an extensive suite of measurements from ground, ship and satellite-based Fourier transform spectrometers, as well as from several aircraft campaigns over North America. The model captures the seasonality of formic and acetic acids well but generally underestimates their concentration, particularly in the Northern midlatitudes. We infer that the source of both carboxylic acids may be up to 50% greater than our estimate and report evidence for a long-lived missing secondary source of carboxylic acids that may be associated with the aging of organic aerosols. Vertical profiles of formic acid in the upper troposphere support a negative temperature dependence of the reaction between formic acid and the hydroxyl radical as suggested by several theoretical studies.

Evolution of organic aerosols in the atmosphere.

Organic aerosol (OA) particles affect climate forcing and human health, but their sources and evolution remain poorly characterized. We present a unifying model framework describing the atmospheric evolution of OA that is constrained by high-time-resolution measurements of its composition, volatility, and oxidation state. OA and OA precursor gases evolve by becoming increasingly oxidized, less volatile, and more hygroscopic, leading to the formation of oxygenated organic aerosol (OOA), with concentrations comparable to those of sulfate aerosol throughout the Northern Hemisphere. Our model framework captures the dynamic aging behavior observed in both the atmosphere and laboratory: It can serve as a basis for improving parameterizations in regional and global models.

Molecular identification and typing of natural whey starter cultures and microbiological and compositional properties of related traditional Mozzarella cheeses.

Cell numbers of presumptive lactic acid bacteria varied markedly between 7 natural whey starter cultures (NWSC) used for producing traditional cows' milk Mozzarella cheeses in the Apulia region of Southern Italy. Taxonomic identification revealed a large diversity at species level, including mesophilic and thermophilic lactobacilli, lactococci, streptococci and enterococci. Randomly Amplified Polymorphic DNA (RAPD-PCR), analysis showed the biodiversity among the strains and, for lactobacilli, some relationships with provenience of the natural starter. Cell numbers of presumptive lactic acid bacteria in the corresponding Mozzarella cheeses were similar or higher than those found in the corresponding NWSC. RAPD-PCR analyses showed that most of the strains in cheese originated from the starter. The gross composition varied markedly between the 7 Mozzarella cheeses and ranged from 53-64% moisture, 17-23% protein, 13-20% fat and 0.50-1.61% salt. The values of pH for several samples were above 6.0. As shown by urea-PAGE of the pH 4.6-insoluble nitrogen fractions, cheese samples were characterized by differences in alpha(S1)- and beta-casein hydrolysis. Cheeses also differed with respect to secondary proteolysis as shown by Principal Component Analysis (PCA) of data from RP-HPLC of the pH 4.6-soluble, pH 4.6-70% ethanol-soluble and 70% ethanol-insoluble nitrogen fractions. These differences were attributed to the different microbial composition of the NWSC. Strain selection and optimization of a protocol for producing a natural whey starter culture to be used by dairy factories of the Apulia region appears to be a pre-requisite to standardize the major traits distinguishing this cheese variety.