Search

AIR SAMPLES WERE COLLECTED AT SITES IN LOS ANGELES AND NEW YORK TO EVALUATE COMPOSITIONAL DETAIL OF THE HYDROCARBONS AND OXIDES OF NITROGEN. THE COMPOSITIONAL DETAILS PROVIDE A WEALTH OF INFORMATION ALLOWING FOR THE ESTIMATION OF SOURCE CONTRIBUTION AND PHOTOCHEMICAL POTENTIAL OF AN AMBIENT ATMOSPHERE. THE NEED TO INVENTORY AN AMBIENT ATMOSPHERE FOR SOURCE CONTRIBUTION IS IMPORTANT FOR EVALUATING CONTROL STRATEGY REQUIRED TO MEET AIR QUALITY STANDARDS. THE MANUSCRIPT DESCRIBES TWO METHODS FOR ESTIMATING VEHICULAR HYDROCARBONS IN AN AMBIENT ATMOSPHERE.

Polycyclic aromatic hydrocarbons are extracted from atmospheric particulate samples with a thermal desorption technique that circumvents the need for lengthy solvent extraction procedures prior to gas chromatographic analysis. The polycyclic aromatic hydrocarbons are extracted by vacuum-sublimation and collected in a cold trap. The sublimed species are then cryogenically focused at the head of a fused silica capillary column by a thermal purging technique and subsequently analyzed. The technique is applicable to screening tests for selected polycyclic aromatic hydrocarbons when used with a sufficiently specific detector, and has the advantages of simplicity and low cost.

Complex hydrocarbon mixtures were reacted for several hours in the presence of nitrogen oxides in a large ultraviolet irradiation chamber. The hydrocarbons were reacted at concentrations of 5, 10, and 20 ppM C in mixes containing /sup 1//2 or 1 ppM NOx. Rates of oxidation of nitric oxide, nitrogen dioxide dosage, hydrocarbon consumption, eye irritation, and yields of peroxyacetyl nitrate (PAN), formaldehyde, and oxidant were measured. If aromatics are substituted for olefins in a hydrocarbon mixture, there is a decrease in both oxidant and PAN dosages. Eye irritation increased with increasing aromatics. These reactivity parameters decreased by replacing aromatics with paraffins. (Air Pollut. Abstr.)

The photooxidation of formaldehyde, acetaldehyde, and propionaldehyde in the presence of nitrogen oxides produces the same products and biological effects as do hydrocarbon photooxidations. Despite the greater consumption of formaldehyde, propionaldehyde is generally the most reactive in terms of higher product yields, eye irritation, and plant damage. Product yields from the photooxidation of formaldehyde-nitrogen oxide tends to be the most sensitive to variation in the ratio of reactants. As a result the oxidant yields from the reactions in the formaldehyde-nitrogen oxide system exceed those of the other systems at higher aldehyde-nitrogen oxide ratios. The photochemical reactivities of the three aldehydes in terms of product yields, eye irritation, and plant damage overlap those of the olefinic and aromatic hydrocarbons. The reduction of formaldehyde and higher molecular weight aldehydes should be accomplished along with reduction of hydrocarbons in emission control strategies for photochemically reactive substances. 32 references, 12 figures, 5 tables.

Multidimensional gas chromatography (MDGC) in combination with simplified sample handling and detection procedures was evaluated for the determination of nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) in particulate matter. Extraction was carried out by sonication. The extract was cleaned up using a short Florisil column, filtered, concentrated, and injected by means of a capillary on-column injector. Heart-cuts taken from the front column were focused on the back column, which was equipped with parallel detectors (flame ionization detector (FID) and nitrogen selective detector (NSD)). Unambiguous identification of chromatographic peaks from the combined information on front and back column retention times and the NSD/FID peak response ratios was demonstrated in the case of 1-nitropyrene. The limit of detection for 1-nitropyrene at 2 x noise was calculated to be 36 picograms under the NSD/FID splitter ratio employed in this study. The recovery of 1-nitropyrene in a National Bureau of Stan...

The photooxidation of part-per-million concentrations of propylene in the presence of similar concentrations of nitric oxide has been investigated. The product yields were measured over a wide range of reactant concentrations and reactant ratios. Series of experiments were carried out with varying light intensities, with both static and dynamic flow conditions. The products measured by colorimetric, gas chromatographic, and various monitoring instruments included nitrogen dioxide, oxidant (ozone and other oxidizing agents), formaldehyde, acetaldehyde, carbon monoxide, peroxyacetyl nitrate, and methyl nitrate. The mechanism of the reactions involved is considered, including, stoichiometry and the role of free radical intermediates. Carbon and nitrogen balances are computed, and difficulties in obtaining balances are considered. 29 references, 13 figures, 5 tables.

The photooxidation of 2 ppm of propylene and 0.5 ppm of nitrogen oxide was investigated under dynamic flow conditions with sulfur dioxide present in the reaction mixtures at concentrations from 0.0 to 1.2 ppm. The statistical t test showed no significant differences in rates of consumption of propylene and nitrogen oxide or in yields of oxidant, peroxyacetyl nitrate, formaldehyde, and acetaldehyde among tests at the various levels of sulfur dioxide, including 0 ppm. Amounts of sulfur dioxide consumed in the reactions ranged from 25 to 60%. Although a sulfur balance was not obtained, appreciable amounts of sulfate were measured as a product of the oxidation of the sulfur dioxide. On the basis of previous investigations, the sulfate is believed to be present as sulfuric acid aerosol. These results suggest that appreciable levels of oxidant may occur in urban atmospheres even when high concentrations of sulfur dioxide are present. 13 references, 2 tables.

The “dichromate” paper developed by Ripley, Clingenpeel, and Hum was used successfully in our laboratory for conversion of nitric oxide to nitrogen dioxide at concentrations up to the 1 ppm level. When this p aper was used for synthetic mixtures with nitric oxide concentrations in the range of 1—3 ppm, the analyses were erratic and values were lower than calculated. After a number of modifications of the procedures for preparing and using the impregnated paper, a modification of the “dichromate” paper was achieved that reduced scatter in the NO analysis and improved conversion efficiency. The efficiency and reproducibility of the modified paper are good enough that efficiency factors may be established to correct data obtained over a period of at least o hours of continuous use at relative humidities (RH) near 50%.