Abstract. Air samples for nonmethane hydrocarbon (NMHC) analysis were collected at two ground-based sites: Alert, Northwest Territories (82.5øN, 62.3øW) and Narwhal ice camp, an ice floe 140 km northwest of Alert, from Julian days 90 to 117, 1994, and on a 2-day aerial survey conducted on Julian days 89 and 90, 1994 over the Arctic archipelago. Several ozone depletion events and concurrent decreases in hydrocarbon concentrations relative to their background levels were observed at Alert and Narwhal ice camp. At Nap•hal, a long period (>-7 days) of ozone depletion was observed during which a clear decay of alkane concentration occurred. A kinetic analysis led to a calculated C1 atom concentration of 4.5 x 103 cm -3 during this period. Several low-ozone periods concurrent with NMHC concentration decreases were observed over a widespread region of the Arctic region (82ø-85øN, and 51ø-65øW). Hydrocarbon measurements during the aerial survey indicated that the low concentrations of these species occurred only in the boundary layer. In all ozone depletion periods, concentration changes of alkanes and toluene were consistent with C1 atom reactions. The changes in ethyne concentration from its background level were in excess of those expected from C1 atom kinetics alone and are attributed to additional Br atom reactions. A box modeling exercise suggested that the C1 and particularly Br atom concentrations required to explain the hydrocarbon behavior are also sufficient to destroy ozone. IntroductionThe depletion of O3 in the boundary layer at the onset of 24 hour daylight in the spring has been reported for several locations in the high Arctic such as Alert ( Hence the relative rates of removal of hydrocarbons can be used as an indicator for the dominance of particular atmospheric photochemical reactions such as those initiated by HO radicals or those started by C1 or Br atoms. 13,169

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

No abstract

Abstract. A 7-year record (1990)(1991)(1992)(1993)(1994)(1995)(1996) of continuous atmospheric methane (CH4) measurements is presented from a remote midcontinental monitoring station at Fraserdale, Ontario (49ø53'N, 81ø34'W). Ninety-six air samples per day were measured with a fully automated gas chromatograph with flame ionization detection. Five-day Lagrangian back trajectories over the 7-year period were used to establish a climatology in the region of the station. The site is predominantly influenced by air flow from northern and high-latitude regions and therefore uniquely positioned to monitor wetland emissions. During winter, CH 4 concentration time series from Fraserdale often match the short-term variability observed at the high Arctic monitoring station at Alert, Northwest Territories (82ø27'N, 61ø31'W). During summer, due to diurnal changes of vertical mixing in the boundary layer, large diurnal cycles in CH 4 mixing ratio up to 150 ppb are observed. The data selected for the afternoon, when the boundary layer is well-mixed, are representative of a larger spatial scale. The mean annual cycle of CH 4 at Fraserdale determined using these selected data is significantly different from annual cycles at other mid-and highnorthern latitude sites thus providing key information for global atmospheric CH 4 models. In late summer the annual cycle at Fraserdale shows a distinct secondary maximum in CH 4. This is the result of advection of air with enhanced CH 4 due to emissions from the extensive wetland areas to the north and northwest. The average growth rate (using selected data) for the period was 5.6 ppb yr -• with a growth rate pattern that is slightly different and out of phase with growth rate changes observed at other high-latitude observing sites by 2 to 6 months. 15,995

Pb206/Pb207 and Pb208/Pb207 isotope ratios were measured in a series of daily atmospheric aerosol samples collected in southern Sweden between 9 February and 30 May 1988. The ratios were observed to vary considerably, depending on the origin of air. 5‐day back‐trajectories were used to classify the samples according to source region: Northwest, Western Europe, East, Eastern Europe, or a combination of two regions. Significant differences in the isotope ratios were found. Unique signatures based on the Pb206/Pb207 and Pb208/Pb207 ratios could be assigned for each region. The signatures were generally consistent with isotope ratios of Swedish and other European gasolines, and with literature values of the isotope ratios of economically significant lead ores used in Europe. A comparison was made between the regional signatures and the Pb206/Pb207 ratios observed in Arctic aerosol samples. Excellent agreement was observed between the Arctic Pb206/Pb207 ratios (1.160) and an average source signature (1.156) calculated from observations in this study using equal contributions from Western Europe, Eastern Europe, and the East as predicted by a chemical transport model.