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The water-soluble organic fractions of aerosol samples collected in Riverside, CA, in summer 2005 were analyzed by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Elemental compositions of about 1000 molecular species were determined in the range m/z 220-420, and four series of organic compounds were identified, fulvic acids, and S-containing, N-containing, and S- and N-containing molecules. Low-resolution product ion spectra proved the presence of organosulfates, organonitrates, and mixed organosulfates and -nitrates that appear to be structurally closely related to each other and to the fulvic acids. This is the first unambiguous detection of fulvic acid molecules and sulfated components in atmospheric aerosol and the first detection even of nitrated analogues. These species provide new clues to the nature of particulate organic matter in atmospheric aerosol.

One of the main hypotheses for the species causing the observed health effects of ambient particulate matter is peroxides and other reactive oxygen species (ROS). However, there is currently very little data available on the concentrations of particle-bound ROS or their behavior in different physical locations and seasons. The concentrations of particle-bound ROS were determined for various size fractions of the aerosol, ranging from 10 nm to 18 μm, in Flushing, New York during the period of January and early February 2004. Sampling was carried out at 3-hour intervals using a MOUDI TM cascade impactor. The collected particles were treated with the non-fluorescent probe dichlorofluorescin (DCFH) that fluoresces when oxidized by the presence of ROS. The measured fluorescent intensities were converted into equivalent hydrogen peroxide concentrations, which were used as indicators of ROS reactivity, by calibrations using H 2 O 2 standards. Diurnal profiles of the ROS concentrations were obtained. Correlations of the particulate ROS concentrations with the intensity of photochemical reaction, estimated secondary organic carbon (SOC) and gas phase OH and HO 2 radical concentrations were explored. The intensity of photochemical reactions and gas phase radical concentrations were found to be moderate factors affecting particulate ROS concentrations. The concentrations of ROS were found to be higher in the submicron size particles of the ambient aerosol.

Previous studies have found significant quantities of oxidative species associated with airborne particulate matter. Although oxidative stress is thought to be an important part of the mechanism by which particles produce adverse health effects, the lack of a suitable method to measure ROS on a routine basis has resulted in no work being undertaken to assess the effects of particle-bound ROS on health. In order to fill this need, an automated monitor for the continuous sampling of ambient aerosol and the measurement of concentrations of ROS on the sampled aerosol was developed. Potential methods to quantify ROS were compared in order to arrive at a suitable method to automate. The dichlorofluorescein (DCFH) fluorescence method was found to be the most non-specific, general indicator of particle-bound oxidants. Hence it was deemed the best suited method for the automated monitor. An integrated samplinganalysis system was designed and constructed based on collection of atmospheric particles in an aqueous slurry, and subsequent detection of the ROS concentration of the slurry using the DCFH fluorescence method. The results of the lab-scale investigation of the ROS sampling-analysis system suggested that the prototype continuous system was capable of detecting particle-bound ROS, and accounting for short-term variabilities in the same. The instrument was found to be capable of detecting nanomolar equivalent concentrations of ROS.

The generation of reactive oxygen species (ROS) and their subsequent induced pulmonary and systemic oxidative stress has been implicated as an important molecular mechanism of PM-mediated toxicity. However, recent work has shown that there is significant ROS associated with ambient PM. In order to understand the formation mechanisms as well as understand the potential health effects of particle-bound oxidative species, the alpha-pinene-O(3) oxidation chemical system was studied to elucidate the structures of reaction products using liquid chromatography-multiple stage mass spectrometry (LC-MS(n)). The classes of compounds identified based on their multiple stage-MS fragmentation patterns, mechanistic considerations of alpha-pinene-O(3) oxidation, and general fragmentation rules, of the products from this reaction system were highly oxygenated species, predominantly containing hydroperoxide and peroxide functional groups. The oxidant species observed were clearly stable for the 1-3 h that elapsed during aerosol collection and analysis, and probably for much longer, thus rendering it possible for these species to bind onto particles forming fine particulate organic peroxides that concentrate on the particles and could deliver concentrated doses of ROS in vivo to tissue.

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