Kenneth A. Brice

Five years of continuous observations of PAN and ozone at a rural location in eastern Canada

Five years of measurements of PAN and O3 at a rural site in eastern Canada are reported. The measurements were made year-round and only interrupted due to instrumental failures. The data are analyzed by advanced statistical methods to determine temporal trends, both for PAN and O3 individually and with respect to their covariance. Since the data are clearly lognormally distributed, this analysis is performed on the logarithmic transform of the data. PAN shows a statistically significant long-term trend but O3 does not. It is argued that this trend may be the result of a change in the overall hydrocarbon composition of the air, since no trend in NOx emissions appears to have taken place over the same time period in eastern North America. Strong seasonal trends in PAN and O3 are found that are similar in overall pattern but differ in detail. The similarity in shape leads to a significant covariance between PAN and O3. The differences in detail can be interpreted as indicative of well-known atmospheric processes, such as the impact of stratospheric folding occurrences leading to additional O3 with respect to PAN in the spring and reduced photochemical activity and lower temperatures in the winter months, which results in a decoupling of the covariance between O3 and PAN. On a day-to-day basis the covariance between PAN and O3 is strong due to the fact that it is essentially determined by meteorological variation. Episodes of alternatively clean and polluted air are observed, each lasting circa 3 days. Seasonal trends in the diurnal patterns are also evident for both compounds: diurnal variation in the summer is considerable but becomes negligible in the winter. PAN displays a larger diurnal variation than O3 in the summer, which can be explained by their relative dry deposition velocities.

Discussion of a lagrangian trajectory model describing long-range transport of oxides of nitrogen, the incorporation of pan in the chemical mechanism, and supporting measurements of pan and nitrate species at rural sites in Ontario, Canada

Abstract The derivation of a highly simplified parameterization of NO x chemistry for use with the AES Lagrangian trajectory model is described. Two versions, both employing essentially independent first-order kinetics are discussed: 1. (1) a one step mechanism: NO 2 → inorganic nitrate and 2. (2) a somewhat more involved reaction scheme including PAN chemistry. Evaluation of model performance is attempted with data from the Canadian Air and Precipitation Monitoring Network (APN). It is shown that both model versions are able to reproduce trends of annual and monthly average atmospheric nitrate concentrations, although the models tend to suggest transport over larger distances than is apparent from the field data. The inclusion of PAN chemistry appears to improve the model performance. However, the model predicts a winter maximum and a summer minimum for the annual profile of PAN, and this is in direct contradiction with field measurements of PAN elsewhere. Initial results from a PAN measurement program conducted at three sites in Ontario are also reported and compared with the second model version. Observations for summer 1982 are predicted quite well, but data collected during March 1983 are substantially overpredicted. It is indicated that during periods of rain, PAN constitutes the major oxidized NO x component. The suggestion is made that this observation is due to a much more efficient precipitation scavenging of nitrate species than of PAN.

Atmospheric Concentrations of Toxaphene on the Coast of Lake Superior

Thirty-seven air samples were collected from September 1996 through December 1997 at Eagle Harbor, Michigan to determine the atmospheric concentration of toxaphene near Lake Superior. The concentrations ranged between 0 and 63 pg/m3, with most less than 20 pg/m3, which agreed well with concurrent measurements over the lake and near Lake Michigan made by other research groups. These concentrations are significantly lower than those measured in 1988 and 1989 in Egbert, a small city in southern Ontario. The phase transition energy was calculated to be 47 kJ/mol, half the value calculated for the Egbert site; this disparity has been seen in comparisons of lakeshore and over-land values for other compounds. If temperature effects are removed, the average toxaphene concentration for the Eagle Harbor samples was 6.4 ± 2.2 pg/m3, which was lower than the 16 pg/m3 average at Egbert, Ontario. This difference in concentration may (or may not) be due to differences in sampling dates or locations or in measurement techniques.

Evaluation of gas chromatography-Fourier transform infrared spectroscopy-mass spectrometry for analysis of phenolic compounds

Abstract A gas chromatography (GC)—infrared (IR) spectroscopy—mass spectrometric (MS) system was evaluated for the identification and quantitation of 50 target phenolic compounds. Six columns of varying polarities were tested to achieve optimum chromatographic resolution of the phenolic compounds. The low polarity columns (HP-1, DB-5) gave resolution of 41 of the 50 phenolics; higher polarity columns (DB-17, DB-1701, DB-210, Nukol) were not as effective. Standard solutions containing 50 target phenolic compounds with concentrations in the range of 10 to 600 ng/μl were prepared. The solutions were injected into the selected column (HP-1) using cool on-column injection with a retention gap and with the IR detector and mass spectrometer run in the full scan mode. Fully resolved peaks could be easily identified and quantitated by either IR spectroscopy or MS. For co-eluting compounds spectral subtraction (IR) or selected ion (MS) techniques were employed as appropriate to identify the individual phenolics.

Studies of toxaphene in technical standard and extracts of background air samples (Point Petre, Ontario) using multidimensional gas chromatography-electron capture detection (MDGC-ECD)

MDGC-ECD procedures have been used to provide insight into the compositional complexity of some of the specific peaks or clusters observed in the gas chromatographic analysis of a technical toxaphene standard, with reference to individual toxaphene congeners (Parlar # components) that are flow commercially available. These investigations have focussed initially upon those peaks and clusters recently identified (Shoeib. M., Brice, K.A., Hoff, R., 1999. Chemosphere 39, 849-871) as dominant constituents of background ambient air. Multiple electron-capturing components have been found to be present in all the species studied: the available individual toxaphene congeners have been matched against these components where possible. In similar fashion, the responses obtained in equivalent gas chromatographic elution windows from the analysis of typical processed air sample extracts have been investigated, with the results showing clear differences relative to the patterns found in the technical toxaphene standard. In most cases, the air sample shows reduced complexity with fewer components present in the cluster. Also, the presence of interfering responses (due to PCBs and other organochlorines) is quite apparent and significant, showing that major problems and errors could arise when using single-column GC-ECD procedures for quantitation of toxaphene in environmental samples. The presence of certain of the Parlar species in the air samples has been confirmed and in most cases these represent the dominant toxaphene component found in the targeted cluster. Furthermore, the persistence of certain congeners in the atmospheric samples appears to be strongly dependent upon chemical structure, since the congeners in question possess an alternating exo-endo chlorine substitution pattern around the six-membered ring in the bornane skeleton. Such persistence is probably the result of lower metabolization of toxaphene residues in soils, water and sediments leading to a similar pattern in the atmosphere following volatilization.