D. F. Smith

Primary Product Distributions from the Reaction of OH with m-, p-Xylene, 1,2,4- and 1,3,5-Trimethylbenzene

A study was conducted to examine the OH-initiated degradation products of the four title compounds in the presence of sub-part-per-million levels of NOx. The oxidation was conducted in a dynamic reactor to minimize the conversion of the aromatic compounds. The experiments were designed to represent reaction pathways that occur in the atmosphere at ambient NO2 concentrations. A wide range of ring-retaining and ring-cleavage products having widely varying yields were measured during the study. For m-xylene, the major primary products observed (with molar yields) were methyl glyoxal (0.40), 4-oxo-2-pentenal (0.12), glyoxal (0.079), and m-tolualdehyde (0.049). For p-xylene, the major primary products were p-tolualdehyde (0.103), 2,5-dimethylphenol (0.13), cis-3-hexene-2,5-dione (0.176), trans-3-hexene-2,5-dione (0.045), 2-methyl-butenedial (0.071), glyoxal (0.394), and methylglyoxal (0.217). Several other reaction products were measured at yields less than 3%. The primary products for OH + 1,2,4-trimethylbenzene were found as follows: methylglyoxal (0.44), glyoxal (0.066), cis-3-hexene-2,5-dione (0.13), trans-3-hexene-2,5-dione (0.031), biacetyl (0.114), 3-methyl-3-hexene-2,5-dione (0.079), and 2-methyl-butenedial (0.045). Six other (ring retaining) products were measured at yields less than 3%. The primary products for OH + 1,3,5-trimethylbenzene were methylglyoxal (0.90), 3-methyl-5-methylidene-5(2H)-furanone (0.1), 3,5-dimethyl-3(2H)-2-furanone (0.1), 3,5-dimethyl-5(2H)-2-furanone biacetyl (0.08), and 2-methyl-4-oxo-2- pentenal (0.05). Three other products were detected at molar yields less than 5%. In some cases, the yields for the ring fragmentation products could only be based on calibrations from surrogate compounds. Yields for several of the unsaturated dicarbonyl compounds have not been reported previously while yields for methylglyoxal, glyoxal, and biacetyl are largely consistent with previous reports. Some of the primary furanone products are the identical to those reported as secondary products in aromatic systems.

Primary Product Distribution from the Reaction of Hydroxyl Radicals with Toluene at ppb NOX Mixing Ratios

When this paper was first published Figure 5 was incorrect. The publisher regrets this oversight. The complete page with correct figure and original pagination is printed overleaf.

Comparison of Chemiluminescence and Ultraviolet Ozone Monitor Responses in the Presence of Humidity and Photochemical Pollutants

The effect of water vapor and other pollutants on ozone monitoring instruments was investigated. Five UV-type and two chemiluminescence-type monitors were employed in this study. The results of the study indicate that in systems containing ozone, water vapor and zero air only, the UV-based monitors showed negligible effects due to humidity. On average, the UV monitors were within 0.5 percent of independently determined ozone values judged to be extremely accurate. The chemiluminescence-based monitors showed systematically higher readings than the UV monitors with added water vapor. The effect was found to be linear with water vapor concentration with an average positive deviation of 3.0 percent per percent H2O at 25 degrees C. For these measurement, ozone concentrations ranged from 85 to 320 ppbv and water concentrations from 1 to 3 percent (i.e., dew point temperatures from 9 to 24 degrees C). These results are largely in agreement with previous studies conducted to measure this interference, although the present study extends the range of water concentrations tested. Studies were also performed with a smog chamber with simulated polluted air (containing paraffinic, olefinic and aromatic hydrocarbon precursors) and varying relative humidities. Although the presence of water vapor did not appear to represent a substantial interference in these systems, a positive interference was observed with the UV monitors. This interference was likely a result of the presence of toluene and some of its aromatic photooxidation products (e.g., benzaldehyde), which can be partially removed from the reference stream by the ozone scrubber within the UV monitor. If the compound absorbs radiation at 254 nm, it is detected as ozone. However, when the results are scaled back to ambient concentrations of toluene and NO(x), the effect appears to be very minor (ca. 3 percent under the study conditions). It is concluded that under atmospheric conditions at moderate pollution and relative humidity levels, both types of instruments can give accurate measurements of the ozone concentration. These potential effects should be recognized when conducting ambient ozone measurements.

The photo-oxidation of automobile emissions: measurements of the transformation products and their mutagenic activity

Abstract Dilute mixtures of automobile emissions (comprising 50% exhaust and 50% surrogate evaporative emissions) were irradiated in a 22.7 m 3 smog chamber and tested for mutagenic activity by using a variant of the Ames test. The exhaust was taken from a single vehicle, a 1977 Ford Mustang equipped with a catalytic converter. Irradiated and nonirradiated gas-phase emissions were used in exposures of the bacteria, Salmonella typhimurium , strains TA100 and TA98. A single set of vehicular operating conditions was used to perform multiple exposures. The mutagenic activities of extracts from the particulate phase were also measured with the standard plate incorporation assay. (In most experiments only direct-acting mutagenic compounds were measured.) The gas-phase data for TA100 and TA98 showed increased activity for the irradiated emissions when compared to the nonirradiated mixture, which exhibited negligible activity with respect to the control values. The particulate phase for both the irradiated and nonirradiated mixtures showed negligible activity when results were compared to the control values for both strains. However, the experimental conditions limited the amount of extractable mass which could be collected in the particulate phase. The measured activities from the gas phase and particulate phase were converted to the number of revertants per cubic meter of effluent (i.e. the mutagenic density ) to compare the contributions of each of these phases to the total mutagenic activity for each strain. Under the experimental conditions of this study, the mutagenic density of the gas-phase component of the irradiated mixture contributed approximately two orders of magnitude more of the total TA100 activity than did the particulate phase. For TA98 the gas-phase component contributed approximately one order of magnitude more. However, caution must be exercised in extrapolating these results to urban atmospheres heavily impacted by automotive emissions, because the bacterial mutagenicity assay was used as a screening method, and additional assays using mammalian systems have not yet been conducted. In addition, only limited number of conditions were able to be tested. The significance and limitations of the results are discussed.

Measurement of Organic Atmospheric Transformation Products by Gas Chromatography

Abstract The photooxidation of hydrocarbons in the atmosphere leads to the formation of organic species which are typically more polar in character than the parent compounds. In recent years, detailed hydrocarbon measurements for C1 to C10 alkanes, alkenes, and aromatics in the atmosphere have involved the use of deactivated canisters and gas chromatography, similar to that described by EPA Method TO-14. However, quantitative measurements of atmospheric polar organic compounds by this method are unreliable. Work in this laboratory frequently involves the analysis of sample mixtures from smog chambers that are used to simulate urban atmospheres for studying the formation of ozone and other potentially hazardous compounds. Over the past several years we have developed an inert cryogenic sampling system and related GC methods for the analysis of the photochemical mixtures which are sensitive, reproducible and provide adequate separation for non-polar hydrocarbons and their polar transformation products. Thes...

Development of a photochemical chamber system for determining measures of reactivity from exhaust of alternative-fuel vehicles

A laboratory system has been developed to evaluate the photochemical characteristics of exhaust generated from alternative-fuel and new technology vehicles. This system is built around an 8-m{sup 3} photochemical chamber constructed of Teflon film. The chamber has been designed to be portable and allow both indoor and outdoor irradiations. Irradiations were conducted on vehicle-fuel combinations. The fuels include reformulated and other alternative fuels. Emissions were collected during Bag 1 of the Federal Test Procedure to ensure sufficient exhaust hydrocarbon during the irradiation. This paper describes the motivation for the experiments, details the experimental design, and the data from irradiations of the exhaust of three fuels using a single vehicle. 10 refs., 5 figs., 3 tabs.