Identification and quantification of aerosol polar oxygenated compounds bearing carboxylic or hydroxyl groups. 2. Organic tracer compounds from monoterpenes.

In this study, a comparison is made of polar organic compounds found in the field with those produced in secondary organic aerosol from laboratory irradiations of natural hydrocarbons and oxides of nitrogen (NOx). The field samples comprised atmospheric particulate matter (PM2.5) collected at Research Triangle Park (RTP), NC, during the summer of 2003, and the laboratory samples originated from the photooxidation of the following monoterpenes: alpha-pinene, beta-pinene, and d-limonene. To determine the structural characteristics of the polar compounds, the filter samples were solvent extracted and derivatized using a technique based on single and multistep derivatizations. The resulting compound derivatives were analyzed by GC-MS in the methane-Cl and El modes. In addition to previously reported biogenic oxidation products (pinic acid, pinonic acid, norpinic acid, nopinone, and pinonaldehyde), seven multifunctional organic compounds were found in both field and laboratory samples. These compounds, which are proposed as possible atmospheric tracers for secondary organic aerosol from monoterpenes, were consistent with the following identifications: 3-isopropyl pentanedioic acid; 3-acetyl pentanedioic acid; 3-carboxy heptanedioic acid; 3-acetyl hexanedioic acid; 2-isopropyl-1,2-dihydroxybutanol; 4-isopropyl-2,4-dihydroxyhexanol; and 3-(2-hydroxy-ethyl)-2,2-dimethyl-cyclobutane carboxylic acid. Initial attempts have been made to quantify the concentrations of these tracer compounds on the basis of surrogate compound calibrations. The occurrence of these compounds in both laboratory and field measurements suggests that secondary organic aerosol originating from biogenic hydrocarbons are contributing to the regional aerosol burden in the southeastern United States. Several of these compounds also appear to contribute to the global aerosol burden in that they have also been identified in Europe and Brazil.

Identification and quantification of aerosol polar oxygenated compounds bearing carboxylic or hydroxyl groups. 1. Method development.

In this study, a new analytical technique was developed for the identification and quantification of multifunctional compounds containing simultaneously at least one hydroxyl or one carboxylic group, or both. This technique is based on derivatizing first the carboxylic group(s) of the multifunctional compound using an alcohol (e.g., methanol, 1-butanol) in the presence of a relatively strong Lewis acid (BF3) as a catalyst. This esterification reaction quickly and quantitatively converts carboxylic acids to their ester forms. The second step is based on silylation of the ester compounds using bis(trimethylsilyl) trifluoroacetamide (BSTFA) as the derivatizing agent. For compounds bearing ketone groups in addition to carboxylic and hydroxyl groups, a third step was used based on PFBHA derivatization of the carbonyls. Different parameters including temperature, reaction time, and effect due to artifacts were optimized. A GC/MS in EI and in methane-CI mode was used for the analysis of these compounds. The new approach was tested on a number of multifunctional compounds. The interpretation of their EI (70 eV) and CI mass spectra shows that critical information is gained leading to unambiguous identification of unknown compounds. For example, when derivatized only with BF(3)-methanol, their mass spectra comprise primary ions at m/z M.+ + 1, M.+ + 29, and M.+ - 31 for compounds bearing only carboxylic groups and M.+ + 1, M.+ + 29, M.+ - 31, and M+. - 17 for those bearing hydroxyl and carboxylic groups. However, when a second derivatization (BSTFA) was used, compounds bearing hydroxyl and carboxylic groups simultaneously show, in addition to the ions observed before, ions at m/z M.+ + 73, M.+ - 15, M.+ - 59, M.+ - 75, M.+ - 89, and 73. To the best of our knowledge, this technique describes systematically for the first time a method for identifying multifunctional oxygenated compounds containing simultaneously one or more hydroxyl and carboxylic acid groups.

Secondary organic aerosol formation from the irradiation of simulated automobile exhaust.

A laboratory study was conducted to evaluate the potential for secondary organic aerosol formation from emissions from automotive exhaust. The goal was to determine to what extent photochemical oxidation products of these hydrocarbons contribute to secondary organic aerosol (SOA) and how well their formation is described by recently developed models for SOA formation. The quality of a surrogate was tested by comparing its reactivity with that from irradiations of authentic automobile exhaust. Experiments for secondary particle formation using the surrogate were conducted in a fixed volume reactor operated in a dynamic mode. The mass concentration of the aerosol was determined from measurements of organic carbon collected on quartz filters and was corrected for the presence of hydrogen, nitrogen, and oxygen atoms in the organic species. A functional group analysis of the aerosol made by Fourier transform infrared (FTIR) spectroscopy indicated

Peroxyacetyl nitrate: measurement of its mutagenic activity using the Salmonella/mammalian microsome reversion assay.

Exposures of Salmonella typhimurium strain TA100 with and without S9 metabolic activation to low ppm levels of pure peroxyacetyl nitrate (PAN) in the gas phase were conducted. Measurements of the gas-phase PAN exposure concentration and the concentration of its decomposition products in surrogate test media led to a measured mutagenic activity of 34 +/- 5 revertants/mumole. The data indicate that PAN is a relatively weak direct-acting mutagen with TA100.