aerosol components are associated with lower tropospheric ozone depletion at polar sunrise. In autumn, aerosol iodine but not bromine has a secondary peak.

However, in that study the analytical sensitivity was not available to determine the isotopic composition of individual weekly aerosol samples during summer when aerosol concen-11,619

Air parcel trajectory data are used in two ways to elucidate the temporal trend analysis of 5 years of peroxyacetyl nitrate (PAN) and O3 observations at a rural site in eastern Canada. In the first method, “probability of residence” contours are constructed to determine the most probable origin of air parcels containing the highest and lowest 10% of PAN and O3 mixing ratios. High PAN is found to emanate always from areas of high anthropogenic activity, except when the transport path is to a large extent over the ocean, especially in the summer. High O3 originates from the same regions except in the winter when because of low photochemical activity, O3 is actually titrated and air from less populated areas is richer in O3. The trajectories indicate that transport at higher altitude leads to higher mixing ratios; this is especially the case for O3 in winter and spring. The complementary method of clustering the trajectories has allowed qualitative derivation of seasonal cycles for background and polluted air masses of different origin. Background air from the north shows a distinct PAN maximum in March; it is discussed that this could be either due to enhanced photochemistry or to the import of polluted air from the Arctic. Polluted air masses show the same March peak, but a second peak in late summer/early fall. Oceanic air from the south has a January maximum in PAN but otherwise is consistently low in PAN. O3 also has a spring maximum, but in polluted air it is broader stretching into the summer. It is postulated that this is due to additional O3 formation in the summer, while in the winter, actual O3 loss is indicated for polluted air. By inference it is deduced that the second PAN peak in polluted air is also due to additional formation in comparison with background air, while in the summer, extra PAN loss mechanisms operate that are less important for O3. Indications for both dry deposition and thermal decomposition have been found.

No abstract

An 11-year record of tropospheric aerosol methanesulfonate (MSA) in the Canadian high Arctic at Alert, Northwest Territories, from 1980 to 1991 shows marked seasonal and long-term variations. By using spectral-analysis techniques, the seasonal cycles and long-term variations have been quantified. There are two distinctly different seasonal peaks with levels of 12-23 ng m '3 in early May and 6-18 ng m '3 in July-August. Over the 11.3 years, the amplitudes of the MSA seasonal cycles and therefore the annual means of MSA concentrations decreased significantly by 33% (3% annually). So far there is no evidence of experimental artifact in this trend, but such a possibility will be further examined. Analysis of MSA monthly anomalies suggests that in spring they are weakly but significantly related to sea surface temperature anomalies (SSTA) in the North Atlantic west of the coast of continental Europe. In summer, MSA monthly anomalies are significantly correlated with SSTA in oceanic regions further north in the North Atlantic off the coast of Norway and in the northeast North Pacific. and summer [Turner and Liss, 1985; Bates et al., 1987; Burgermeister et al., 1990; Erickson et al., 1990; Leck and Rodhe, 1991; Tarfason, 1991]. What evidence existed on northern polar spatial and temporal variation of MSA prior to 1991 was presented by Li et al . [1993] and Li and Winchester [1989]. In a companion paper of the present study [Li and Battle, this issue] (hereafter referred to as paper 1), a detailed description of measurement methodology and other implications of the data is given. In addition, the contribution of marine biogenic aerosols to total sulfate is assessed using simultaneous observations of major aerosol ions, trace elements, and sulfur isotopes. The biogenic ratio of MSA to sulfate in air reaching northern regions is also examined. This paper augments the previously limited observations and analyses with an 11-year record of aerosol MSA measurements at ground level at Alert, Northwest Territories (82.5øN, 62.3øW), between July 1980 and August 1991. We present a