Regional Trace Element and Sulfate Transport

The goal of this paper was to investigate the transport of atmospheric sulfate and trace elements across the northeastern U.S.A. Data from a number of sites-Underhill (VT), Whiteface Mountain (NY), Mayvil le (NY), Laurel Hill and Allegheny Mountain (PA) and Deep Creek Lake (MD)-in August 1983 were considered. Sulfate was found to be regional in nature, displaying temporal variations which were similar at sites separated by large distances (several hundred kilometers) under certain meteorological conditions. Selenium was the only trace species investigated which displayed a regional character, though it too was influenced by local sources. Other elements, such as As and V displayed a somewhat regional nature but less than that observed for sulfate and selenium. The 5-day period 16-20 August, a period of elevated sulfate at all sites, was investigated as to the generality of regional signatures, utilizing trace element ratios. The inter-site variabilities in elemental ratios among the Allegheny, Laurel, Deep Creek and Mayvil le sites were generally small (a factor of 2 or less) and well within the variabilities at a given site from one day to another. But there were exceptions, probably reflecting influences of local sources. Comparison with earlier trace-element data from the same region suggests that temporal variations may be less than spatial ones. Together the data indicate that it is important to obtain data from multiple sites and periods within a region in any effort to construct a regional signature. An unusually clean period, 13-15 August, with steady air mass advection from the northeast to all sites, was investigated to evaluate the conservation of regional signatures into downwind regions. The interregional differences in trace element ratios proved to be far larger than the intra-regional ones-an order of magnitude in some cases, attributable mostly to addition of trace elements in the downwind region. The ability to identify in one region the signature from another region appears to be problematic. However, aerosol trace element ratios are found to be a powerful tool for investigating regional source influences when used in concert with meteorological information. Key word index: Long-range transport, aerosols, size distributions, trajectories.