Abstract. Observations of ozone mixing ratios in the lower troposphere of Arctic Canada in April 1994 are summarized. Except during a brief period of anomalous transport from high altitude, air depleted in ozone was always observed above sea ice and snow throughout the northern Ellesmere Island/Lincoln Sea region, or whenever air was sampled which had been in recent contact with sea ice and snow. Ozone mixing ratios observed at a camp on the sea ice north of Alert were consistent with a 1992 study. Observations at the ice camp confirmed that ozone was depleted more frequently (74% of all observations <5 ppbv) than at coastal and inland sites near Alert (10% of observations <5 ppbv). Mixing ratios briefly attained a maximum of 36 ppbv at the ice camp but were normally completely depleted or below typical free tropospheric levels of 35-45 ppbv observed elsewhere in the region. Aircraft measurements and vertical profiles of ozone and meteorological parameters from balloon sondes confirmed that ozone depletion existed in a layer above the sea ice, from the surface up to heights of 200-400 m. Some observations showed a very abrupt transition between depleted and nondepleted conditions at the upper boundary of the layer. The occurrence of a layer of fully depleted ozone was well correlated with surface high-pressure systems. At Alert the appearance of air that was fully depleted in ozone was driven by advection from ocean areas to the north. A fortuitous set of meteorological conditions allowed the use of a simple model for testing general aspects of some proposed hypotheses for ozone destruction, during a period when it is believed the depleted layer was forming. It was found that the observed rate of ozone destruction would require levels of HO and C1 atoms much higher than would be expected for the prevailing conditions but reasonable concentrations of Br --1 atoms. It was also found that an effective ozone deposition velocity of 0.1-0.2 cm s could account for the observed depletion rate during this period. That is, the observed rate of ozone depiction during formation of a depleted layer was consistent with either a volume sink or a surface sink for ozone. 0148-0227/98/97JD-02888509.00 depleted air at Alert was meteorologically modulated; that is, ozone-depleted air was advected from ocean areas to the north which were source regions for atmospheric Br or other ozonedestroying constituents.Ozone mixing ratios and related meteorological parameters observed from a variety of platforms are summarized here.More detailed data were obtained on the horizontal and vertical distribution of ozone depletion and the broader links between ozone depletion and meteorology. A fortuitous set of meteorological circumstances presented an opportunity for contrasting characteristic periods of depleted and nondepleted conditions. ExperimentOzone mixing ratios were measured during four aircraft flights at the beginning of PSE94 (Figure 1
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.
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